Sébastien Deleuze
2 months ago
9 changed files with 11 additions and 837 deletions
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[[dynamic-language]] |
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= Dynamic Language Support |
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|
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Spring provides comprehensive support for using classes and objects that have been |
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defined by using a dynamic language (such as Groovy) with Spring. This support lets |
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you write any number of classes in a supported dynamic language and have the Spring |
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container transparently instantiate, configure, and dependency inject the resulting |
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objects. |
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|
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Spring's scripting support primarily targets Groovy and BeanShell. Beyond those |
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specifically supported languages, the JSR-223 scripting mechanism is supported |
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for integration with any JSR-223 capable language provider, for example, JRuby. |
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|
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You can find fully working examples of where this dynamic language support can be |
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immediately useful in xref:languages/dynamic.adoc#dynamic-language-scenarios[Scenarios]. |
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|
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|
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[[dynamic-language-a-first-example]] |
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== A First Example |
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The bulk of this chapter is concerned with describing the dynamic language support in |
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detail. Before diving into all of the ins and outs of the dynamic language support, |
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we look at a quick example of a bean defined in a dynamic language. The dynamic |
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language for this first bean is Groovy. (The basis of this example was taken from the |
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Spring test suite. If you want to see equivalent examples in any of the other |
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supported languages, take a look at the source code). |
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|
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The next example shows the `Messenger` interface, which the Groovy bean is going to |
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implement. Note that this interface is defined in plain Java. Dependent objects that |
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are injected with a reference to the `Messenger` do not know that the underlying |
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implementation is a Groovy script. The following listing shows the `Messenger` interface: |
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[source,java,indent=0,subs="verbatim,quotes",chomp="-packages"] |
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---- |
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package org.springframework.scripting; |
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public interface Messenger { |
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String getMessage(); |
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} |
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---- |
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The following example defines a class that has a dependency on the `Messenger` interface: |
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[source,java,indent=0,subs="verbatim,quotes",chomp="-packages"] |
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---- |
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package org.springframework.scripting; |
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public class DefaultBookingService implements BookingService { |
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private Messenger messenger; |
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public void setMessenger(Messenger messenger) { |
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this.messenger = messenger; |
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} |
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public void processBooking() { |
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// use the injected Messenger object... |
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} |
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} |
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---- |
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The following example implements the `Messenger` interface in Groovy: |
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[source,groovy,indent=0,subs="verbatim,quotes",chomp="-packages",fold="none"] |
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---- |
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package org.springframework.scripting.groovy |
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// Import the Messenger interface (written in Java) that is to be implemented |
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import org.springframework.scripting.Messenger |
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// Define the implementation in Groovy in file 'Messenger.groovy' |
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class GroovyMessenger implements Messenger { |
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String message |
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} |
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---- |
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|
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[NOTE] |
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==== |
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To use the custom dynamic language tags to define dynamic-language-backed beans, you |
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need to have the XML Schema preamble at the top of your Spring XML configuration file. |
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You also need to use a Spring `ApplicationContext` implementation as your IoC |
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container. Using the dynamic-language-backed beans with a plain `BeanFactory` |
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implementation is supported, but you have to manage the plumbing of the Spring internals |
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to do so. |
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For more information on schema-based configuration, see xref:languages/dynamic.adoc#xsd-schemas-lang[XML Schema-based Configuration] |
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. |
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==== |
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Finally, the following example shows the bean definitions that effect the injection of the |
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Groovy-defined `Messenger` implementation into an instance of the |
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`DefaultBookingService` class: |
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[source,xml,indent=0,subs="verbatim,quotes"] |
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---- |
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<?xml version="1.0" encoding="UTF-8"?> |
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<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" |
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xmlns:lang="http://www.springframework.org/schema/lang" |
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xsi:schemaLocation=" |
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http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd |
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http://www.springframework.org/schema/lang https://www.springframework.org/schema/lang/spring-lang.xsd"> |
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<!-- this is the bean definition for the Groovy-backed Messenger implementation --> |
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<lang:groovy id="messenger" script-source="classpath:Messenger.groovy"> |
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<lang:property name="message" value="I Can Do The Frug" /> |
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</lang:groovy> |
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<!-- an otherwise normal bean that will be injected by the Groovy-backed Messenger --> |
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<bean id="bookingService" class="x.y.DefaultBookingService"> |
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<property name="messenger" ref="messenger" /> |
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</bean> |
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</beans> |
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---- |
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|
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The `bookingService` bean (a `DefaultBookingService`) can now use its private `messenger` |
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member variable as normal, because the `Messenger` instance that was injected into it is |
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a `Messenger` instance. There is nothing special going on here -- just plain Java and |
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plain Groovy. |
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Hopefully, the preceding XML snippet is self-explanatory, but do not worry unduly if it is not. |
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Keep reading for the in-depth detail on the whys and wherefores of the preceding configuration. |
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[[dynamic-language-beans]] |
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== Defining Beans that Are Backed by Dynamic Languages |
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This section describes exactly how you define Spring-managed beans in any of the |
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supported dynamic languages. |
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Note that this chapter does not attempt to explain the syntax and idioms of the supported |
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dynamic languages. For example, if you want to use Groovy to write certain of the classes |
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in your application, we assume that you already know Groovy. If you need further details |
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about the dynamic languages themselves, see |
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xref:languages/dynamic.adoc#dynamic-language-resources[Further Resources] at the end of |
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this chapter. |
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[[dynamic-language-beans-concepts]] |
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=== Common Concepts |
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The steps involved in using dynamic-language-backed beans are as follows: |
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. Write the test for the dynamic language source code (naturally). |
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. Then write the dynamic language source code itself. |
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. Define your dynamic-language-backed beans by using the appropriate `<lang:language/>` |
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element in the XML configuration (you can define such beans programmatically by |
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using the Spring API, although you will have to consult the source code for |
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directions on how to do this, as this chapter does not cover this type of advanced configuration). |
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Note that this is an iterative step. You need at least one bean definition for each dynamic |
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language source file (although multiple bean definitions can reference the same source file). |
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|
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The first two steps (testing and writing your dynamic language source files) are beyond |
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the scope of this chapter. See the language specification and reference manual |
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for your chosen dynamic language and crack on with developing your dynamic language |
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source files. You first want to read the rest of this chapter, though, as |
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Spring's dynamic language support does make some (small) assumptions about the contents |
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of your dynamic language source files. |
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[[dynamic-language-beans-concepts-xml-language-element]] |
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==== The <lang:language/> element |
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The final step in the list in the xref:languages/dynamic.adoc#dynamic-language-beans-concepts[preceding section] |
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involves defining dynamic-language-backed bean definitions, one for each bean that you |
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want to configure (this is no different from normal JavaBean configuration). However, |
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instead of specifying the fully qualified class name of the class that is to be |
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instantiated and configured by the container, you can use the `<lang:language/>` |
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element to define the dynamic language-backed bean. |
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|
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Each of the supported languages has a corresponding `<lang:language/>` element: |
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* `<lang:groovy/>` (Groovy) |
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* `<lang:bsh/>` (BeanShell) |
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* `<lang:std/>` (JSR-223, for example, with JRuby) |
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The exact attributes and child elements that are available for configuration depends on |
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exactly which language the bean has been defined in (the language-specific sections |
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later in this chapter detail this). |
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|
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[[dynamic-language-refreshable-beans]] |
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==== Refreshable Beans |
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One of the (and perhaps the single) most compelling value adds of the dynamic language |
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support in Spring is the "`refreshable bean`" feature. |
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A refreshable bean is a dynamic-language-backed bean. With a small amount of |
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configuration, a dynamic-language-backed bean can monitor changes in its underlying |
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source file resource and then reload itself when the dynamic language source file is |
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changed (for example, when you edit and save changes to the file on the file system). |
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|
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This lets you deploy any number of dynamic language source files as part of an |
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application, configure the Spring container to create beans backed by dynamic |
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language source files (using the mechanisms described in this chapter), and (later, |
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as requirements change or some other external factor comes into play) edit a dynamic |
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language source file and have any change they make be reflected in the bean that is |
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backed by the changed dynamic language source file. There is no need to shut down a |
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running application (or redeploy in the case of a web application). The |
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dynamic-language-backed bean so amended picks up the new state and logic from the |
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changed dynamic language source file. |
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NOTE: This feature is off by default. |
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|
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Now we can take a look at an example to see how easy it is to start using refreshable |
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beans. To turn on the refreshable beans feature, you have to specify exactly one |
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additional attribute on the `<lang:language/>` element of your bean definition. So, |
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if we stick with xref:languages/dynamic.adoc#dynamic-language-a-first-example[the example] from earlier in |
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this chapter, the following example shows what we would change in the Spring XML |
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configuration to effect refreshable beans: |
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[source,xml,indent=0,subs="verbatim,quotes"] |
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---- |
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<beans> |
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<!-- this bean is now 'refreshable' due to the presence of the 'refresh-check-delay' attribute --> |
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<lang:groovy id="messenger" |
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refresh-check-delay="5000" <!-- switches refreshing on with 5 seconds between checks --> |
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script-source="classpath:Messenger.groovy"> |
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<lang:property name="message" value="I Can Do The Frug" /> |
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</lang:groovy> |
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<bean id="bookingService" class="x.y.DefaultBookingService"> |
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<property name="messenger" ref="messenger" /> |
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</bean> |
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</beans> |
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---- |
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|
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That really is all you have to do. The `refresh-check-delay` attribute defined on the |
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`messenger` bean definition is the number of milliseconds after which the bean is |
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refreshed with any changes made to the underlying dynamic language source file. |
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You can turn off the refresh behavior by assigning a negative value to the |
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`refresh-check-delay` attribute. Remember that, by default, the refresh behavior is |
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disabled. If you do not want the refresh behavior, do not define the attribute. |
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If we then run the following application, we can exercise the refreshable feature. |
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(Please excuse the "`jumping-through-hoops-to-pause-the-execution`" shenanigans |
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in this next slice of code.) The `System.in.read()` call is only there so that the |
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execution of the program pauses while you (the developer in this scenario) go off |
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and edit the underlying dynamic language source file so that the refresh triggers |
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on the dynamic-language-backed bean when the program resumes execution. |
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The following listing shows this sample application: |
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[source,java,indent=0,subs="verbatim,quotes"] |
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---- |
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import org.springframework.context.ApplicationContext; |
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import org.springframework.context.support.ClassPathXmlApplicationContext; |
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import org.springframework.scripting.Messenger; |
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public final class Boot { |
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public static void main(final String[] args) throws Exception { |
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ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml"); |
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Messenger messenger = (Messenger) ctx.getBean("messenger"); |
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System.out.println(messenger.getMessage()); |
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// pause execution while I go off and make changes to the source file... |
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System.in.read(); |
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System.out.println(messenger.getMessage()); |
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} |
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} |
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---- |
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Assume then, for the purposes of this example, that all calls to the `getMessage()` |
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method of `Messenger` implementations have to be changed such that the message is |
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surrounded by quotation marks. The following listing shows the changes that you |
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(the developer) should make to the `Messenger.groovy` source file when the |
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execution of the program is paused: |
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[source,groovy,indent=0,subs="verbatim,quotes",chomp="-packages"] |
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---- |
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package org.springframework.scripting |
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class GroovyMessenger implements Messenger { |
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private String message = "Bingo" |
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public String getMessage() { |
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// change the implementation to surround the message in quotes |
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return "'" + this.message + "'" |
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} |
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public void setMessage(String message) { |
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this.message = message |
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} |
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} |
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---- |
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When the program runs, the output before the input pause will be `I Can Do The Frug`. |
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After the change to the source file is made and saved and the program resumes execution, |
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the result of calling the `getMessage()` method on the dynamic-language-backed |
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`Messenger` implementation is `'I Can Do The Frug'` (notice the inclusion of the |
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additional quotation marks). |
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Changes to a script do not trigger a refresh if the changes occur within the window of |
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the `refresh-check-delay` value. Changes to the script are not actually picked up until |
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a method is called on the dynamic-language-backed bean. It is only when a method is |
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called on a dynamic-language-backed bean that it checks to see if its underlying script |
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source has changed. Any exceptions that relate to refreshing the script (such as |
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encountering a compilation error or finding that the script file has been deleted) |
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results in a fatal exception being propagated to the calling code. |
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The refreshable bean behavior described earlier does not apply to dynamic language |
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source files defined with the `<lang:inline-script/>` element notation (see |
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xref:languages/dynamic.adoc#dynamic-language-beans-inline[Inline Dynamic Language Source Files]). |
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Additionally, it applies only to beans where changes to the underlying source file can |
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actually be detected (for example, by code that checks the last modified date of a |
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dynamic language source file that exists on the file system). |
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[[dynamic-language-beans-inline]] |
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==== Inline Dynamic Language Source Files |
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The dynamic language support can also cater to dynamic language source files that are |
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embedded directly in Spring bean definitions. More specifically, the |
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`<lang:inline-script/>` element lets you define dynamic language source immediately |
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inside a Spring configuration file. An example might clarify how the inline script |
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feature works: |
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[source,xml,indent=0,subs="verbatim,quotes"] |
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---- |
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<lang:groovy id="messenger"> |
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<lang:inline-script> |
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package org.springframework.scripting.groovy |
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import org.springframework.scripting.Messenger |
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class GroovyMessenger implements Messenger { |
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String message |
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} |
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</lang:inline-script> |
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<lang:property name="message" value="I Can Do The Frug" /> |
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</lang:groovy> |
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---- |
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|
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If we put to one side the issues surrounding whether it is good practice to define |
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dynamic language source inside a Spring configuration file, the `<lang:inline-script/>` |
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element can be useful in some scenarios. For instance, we might want to quickly add a |
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Spring `Validator` implementation to a Spring MVC `Controller`. This is but a moment's |
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work using inline source. (See |
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xref:languages/dynamic.adoc#dynamic-language-scenarios-validators[Scripted Validators] |
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for such an example.) |
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|
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[[dynamic-language-beans-ctor-injection]] |
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==== Understanding Constructor Injection in the Context of Dynamic-language-backed Beans |
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|
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There is one very important thing to be aware of with regard to Spring's dynamic |
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language support. Namely, you can not (currently) supply constructor arguments |
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to dynamic-language-backed beans (and, hence, constructor-injection is not available for |
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dynamic-language-backed beans). In the interests of making this special handling of |
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constructors and properties 100% clear, the following mixture of code and configuration |
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does not work: |
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|
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.An approach that cannot work |
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[source,groovy,indent=0,subs="verbatim,quotes",chomp="-packages"] |
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---- |
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package org.springframework.scripting.groovy |
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import org.springframework.scripting.Messenger |
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// from the file 'Messenger.groovy' |
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class GroovyMessenger implements Messenger { |
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GroovyMessenger() {} |
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// this constructor is not available for Constructor Injection |
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GroovyMessenger(String message) { |
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this.message = message; |
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} |
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|
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String message |
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|
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String anotherMessage |
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} |
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---- |
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[source,xml,indent=0,subs="verbatim,quotes"] |
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---- |
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<lang:groovy id="badMessenger" |
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script-source="classpath:Messenger.groovy"> |
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<!-- this next constructor argument will not be injected into the GroovyMessenger --> |
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<!-- in fact, this isn't even allowed according to the schema --> |
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<constructor-arg value="This will not work" /> |
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|
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<!-- only property values are injected into the dynamic-language-backed object --> |
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<lang:property name="anotherMessage" value="Passed straight through to the dynamic-language-backed object" /> |
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|
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</lang> |
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---- |
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|
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In practice this limitation is not as significant as it first appears, since setter |
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injection is the injection style favored by the overwhelming majority of developers |
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(we leave the discussion as to whether that is a good thing to another day). |
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|
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[[dynamic-language-beans-groovy]] |
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=== Groovy Beans |
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|
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This section describes how to use beans defined in Groovy in Spring. |
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|
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The Groovy homepage includes the following description: |
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|
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"`Groovy is an agile dynamic language for the Java 2 Platform that has many of the |
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features that people like so much in languages like Python, Ruby and Smalltalk, making |
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them available to Java developers using a Java-like syntax.`" |
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|
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If you have read this chapter straight from the top, you have already |
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xref:languages/dynamic.adoc#dynamic-language-a-first-example[seen an example] of a Groovy-dynamic-language-backed |
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bean. Now consider another example (again using an example from the Spring test suite): |
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|
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[source,java,indent=0,subs="verbatim,quotes",chomp="-packages"] |
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---- |
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package org.springframework.scripting; |
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|
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public interface Calculator { |
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|
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int add(int x, int y); |
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} |
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---- |
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|
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The following example implements the `Calculator` interface in Groovy: |
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|
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[source,groovy,indent=0,subs="verbatim,quotes",chomp="-packages"] |
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---- |
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package org.springframework.scripting.groovy |
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|
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// from the file 'calculator.groovy' |
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class GroovyCalculator implements Calculator { |
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|
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int add(int x, int y) { |
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x + y |
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} |
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} |
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---- |
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|
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The following bean definition uses the calculator defined in Groovy: |
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|
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[source,xml,indent=0,subs="verbatim,quotes"] |
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---- |
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<!-- from the file 'beans.xml' --> |
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<beans> |
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<lang:groovy id="calculator" script-source="classpath:calculator.groovy"/> |
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</beans> |
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---- |
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|
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Finally, the following small application exercises the preceding configuration: |
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|
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[source,java,indent=0,subs="verbatim,quotes",chomp="-packages"] |
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---- |
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package org.springframework.scripting; |
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|
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import org.springframework.context.ApplicationContext; |
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import org.springframework.context.support.ClassPathXmlApplicationContext; |
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|
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public class Main { |
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|
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public static void main(String[] args) { |
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ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml"); |
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Calculator calc = ctx.getBean("calculator", Calculator.class); |
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System.out.println(calc.add(2, 8)); |
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} |
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} |
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---- |
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|
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The resulting output from running the above program is (unsurprisingly) `10`. |
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(For more interesting examples, see the dynamic language showcase project for a more |
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complex example or see the examples xref:languages/dynamic.adoc#dynamic-language-scenarios[Scenarios] later in this chapter). |
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|
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You must not define more than one class per Groovy source file. While this is perfectly |
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legal in Groovy, it is (arguably) a bad practice. In the interests of a consistent |
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approach, you should (in the opinion of the Spring team) respect the standard Java |
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conventions of one (public) class per source file. |
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|
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[[dynamic-language-beans-groovy-customizer]] |
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==== Customizing Groovy Objects by Using a Callback |
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|
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The `GroovyObjectCustomizer` interface is a callback that lets you hook additional |
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creation logic into the process of creating a Groovy-backed bean. For example, |
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implementations of this interface could invoke any required initialization methods, |
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set some default property values, or specify a custom `MetaClass`. The following listing |
||||
shows the `GroovyObjectCustomizer` interface definition: |
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|
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[source,java,indent=0,subs="verbatim,quotes"] |
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---- |
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public interface GroovyObjectCustomizer { |
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|
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void customize(GroovyObject goo); |
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} |
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---- |
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|
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The Spring Framework instantiates an instance of your Groovy-backed bean and then |
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passes the created `GroovyObject` to the specified `GroovyObjectCustomizer` (if one |
||||
has been defined). You can do whatever you like with the supplied `GroovyObject` |
||||
reference. We expect that most people want to set a custom `MetaClass` with this |
||||
callback, and the following example shows how to do so: |
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|
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[source,java,indent=0,subs="verbatim,quotes"] |
||||
---- |
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public final class SimpleMethodTracingCustomizer implements GroovyObjectCustomizer { |
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|
||||
public void customize(GroovyObject goo) { |
||||
DelegatingMetaClass metaClass = new DelegatingMetaClass(goo.getMetaClass()) { |
||||
|
||||
public Object invokeMethod(Object object, String methodName, Object[] arguments) { |
||||
System.out.println("Invoking '" + methodName + "'."); |
||||
return super.invokeMethod(object, methodName, arguments); |
||||
} |
||||
}; |
||||
metaClass.initialize(); |
||||
goo.setMetaClass(metaClass); |
||||
} |
||||
|
||||
} |
||||
---- |
||||
|
||||
A full discussion of meta-programming in Groovy is beyond the scope of the Spring |
||||
reference manual. See the relevant section of the Groovy reference manual or do a |
||||
search online. Plenty of articles address this topic. Actually, making use of a |
||||
`GroovyObjectCustomizer` is easy if you use the Spring namespace support, as the |
||||
following example shows: |
||||
|
||||
[source,xml,indent=0,subs="verbatim,quotes"] |
||||
---- |
||||
<!-- define the GroovyObjectCustomizer just like any other bean --> |
||||
<bean id="tracingCustomizer" class="example.SimpleMethodTracingCustomizer"/> |
||||
|
||||
<!-- ... and plug it into the desired Groovy bean via the 'customizer-ref' attribute --> |
||||
<lang:groovy id="calculator" |
||||
script-source="classpath:org/springframework/scripting/groovy/Calculator.groovy" |
||||
customizer-ref="tracingCustomizer"/> |
||||
---- |
||||
|
||||
If you do not use the Spring namespace support, you can still use the |
||||
`GroovyObjectCustomizer` functionality, as the following example shows: |
||||
|
||||
[source,xml,indent=0,subs="verbatim,quotes"] |
||||
---- |
||||
<bean id="calculator" class="org.springframework.scripting.groovy.GroovyScriptFactory"> |
||||
<constructor-arg value="classpath:org/springframework/scripting/groovy/Calculator.groovy"/> |
||||
<!-- define the GroovyObjectCustomizer (as an inner bean) --> |
||||
<constructor-arg> |
||||
<bean id="tracingCustomizer" class="example.SimpleMethodTracingCustomizer"/> |
||||
</constructor-arg> |
||||
</bean> |
||||
|
||||
<bean class="org.springframework.scripting.support.ScriptFactoryPostProcessor"/> |
||||
---- |
||||
|
||||
NOTE: You may also specify a Groovy `CompilationCustomizer` (such as an `ImportCustomizer`) |
||||
or even a full Groovy `CompilerConfiguration` object in the same place as Spring's |
||||
`GroovyObjectCustomizer`. Furthermore, you may set a common `GroovyClassLoader` with custom |
||||
configuration for your beans at the `ConfigurableApplicationContext.setClassLoader` level; |
||||
this also leads to shared `GroovyClassLoader` usage and is therefore recommendable in case of |
||||
a large number of scripted beans (avoiding an isolated `GroovyClassLoader` instance per bean). |
||||
|
||||
[[dynamic-language-beans-bsh]] |
||||
=== BeanShell Beans |
||||
|
||||
This section describes how to use BeanShell beans in Spring. |
||||
|
||||
The https://beanshell.github.io/intro.html[BeanShell homepage] includes the following |
||||
description: |
||||
|
||||
---- |
||||
BeanShell is a small, free, embeddable Java source interpreter with dynamic language |
||||
features, written in Java. BeanShell dynamically runs standard Java syntax and |
||||
extends it with common scripting conveniences such as loose types, commands, and method |
||||
closures like those in Perl and JavaScript. |
||||
---- |
||||
|
||||
In contrast to Groovy, BeanShell-backed bean definitions require some (small) additional |
||||
configuration. The implementation of the BeanShell dynamic language support in Spring is |
||||
interesting, because Spring creates a JDK dynamic proxy that implements all of the |
||||
interfaces that are specified in the `script-interfaces` attribute value of the |
||||
`<lang:bsh>` element (this is why you must supply at least one interface in the value |
||||
of the attribute, and, consequently, program to interfaces when you use BeanShell-backed |
||||
beans). This means that every method call on a BeanShell-backed object goes through the |
||||
JDK dynamic proxy invocation mechanism. |
||||
|
||||
Now we can show a fully working example of using a BeanShell-based bean that implements |
||||
the `Messenger` interface that was defined earlier in this chapter. We again show the |
||||
definition of the `Messenger` interface: |
||||
|
||||
[source,java,indent=0,subs="verbatim,quotes",chomp="-packages"] |
||||
---- |
||||
package org.springframework.scripting; |
||||
|
||||
public interface Messenger { |
||||
|
||||
String getMessage(); |
||||
} |
||||
---- |
||||
|
||||
The following example shows the BeanShell "`implementation`" (we use the term loosely here) |
||||
of the `Messenger` interface: |
||||
|
||||
[source,java,indent=0,subs="verbatim,quotes"] |
||||
---- |
||||
String message; |
||||
|
||||
String getMessage() { |
||||
return message; |
||||
} |
||||
|
||||
void setMessage(String aMessage) { |
||||
message = aMessage; |
||||
} |
||||
---- |
||||
|
||||
The following example shows the Spring XML that defines an "`instance`" of the above |
||||
"`class`" (again, we use these terms very loosely here): |
||||
|
||||
[source,xml,indent=0,subs="verbatim,quotes"] |
||||
---- |
||||
<lang:bsh id="messageService" script-source="classpath:BshMessenger.bsh" |
||||
script-interfaces="org.springframework.scripting.Messenger"> |
||||
|
||||
<lang:property name="message" value="Hello World!" /> |
||||
</lang:bsh> |
||||
---- |
||||
|
||||
See xref:languages/dynamic.adoc#dynamic-language-scenarios[Scenarios] for some scenarios |
||||
where you might want to use BeanShell-based beans. |
||||
|
||||
|
||||
[[dynamic-language-scenarios]] |
||||
== Scenarios |
||||
|
||||
The possible scenarios where defining Spring managed beans in a scripting language would |
||||
be beneficial are many and varied. This section describes two possible use cases for the |
||||
dynamic language support in Spring. |
||||
|
||||
[[dynamic-language-scenarios-controllers]] |
||||
=== Scripted Spring MVC Controllers |
||||
|
||||
One group of classes that can benefit from using dynamic-language-backed beans is that |
||||
of Spring MVC controllers. In pure Spring MVC applications, the navigational flow |
||||
through a web application is, to a large extent, determined by code encapsulated within |
||||
your Spring MVC controllers. As the navigational flow and other presentation layer logic |
||||
of a web application needs to be updated to respond to support issues or changing |
||||
business requirements, it may well be easier to effect any such required changes by |
||||
editing one or more dynamic language source files and seeing those changes being |
||||
immediately reflected in the state of a running application. |
||||
|
||||
Remember that, in the lightweight architectural model espoused by projects such as |
||||
Spring, you typically aim to have a really thin presentation layer, with all |
||||
the meaty business logic of an application being contained in the domain and service |
||||
layer classes. Developing Spring MVC controllers as dynamic-language-backed beans lets |
||||
you change presentation layer logic by editing and saving text files. Any |
||||
changes to such dynamic language source files is (depending on the configuration) |
||||
automatically reflected in the beans that are backed by dynamic language source files. |
||||
|
||||
NOTE: To effect this automatic "`pickup`" of any changes to dynamic-language-backed |
||||
beans, you have to enable the "`refreshable beans`" functionality. See |
||||
xref:languages/dynamic.adoc#dynamic-language-refreshable-beans[Refreshable Beans] for a full treatment of this feature. |
||||
|
||||
The following example shows an `org.springframework.web.servlet.mvc.Controller` implemented |
||||
by using the Groovy dynamic language: |
||||
|
||||
[source,groovy,indent=0,subs="verbatim,quotes",chomp="-packages"] |
||||
---- |
||||
package org.springframework.showcase.fortune.web |
||||
|
||||
import org.springframework.showcase.fortune.service.FortuneService |
||||
import org.springframework.showcase.fortune.domain.Fortune |
||||
import org.springframework.web.servlet.ModelAndView |
||||
import org.springframework.web.servlet.mvc.Controller |
||||
|
||||
import jakarta.servlet.http.HttpServletRequest |
||||
import jakarta.servlet.http.HttpServletResponse |
||||
|
||||
// from the file '/WEB-INF/groovy/FortuneController.groovy' |
||||
class FortuneController implements Controller { |
||||
|
||||
@Property FortuneService fortuneService |
||||
|
||||
ModelAndView handleRequest(HttpServletRequest request, |
||||
HttpServletResponse httpServletResponse) { |
||||
return new ModelAndView("tell", "fortune", this.fortuneService.tellFortune()) |
||||
} |
||||
} |
||||
---- |
||||
|
||||
[source,xml,indent=0,subs="verbatim,quotes"] |
||||
---- |
||||
<lang:groovy id="fortune" |
||||
refresh-check-delay="3000" |
||||
script-source="/WEB-INF/groovy/FortuneController.groovy"> |
||||
<lang:property name="fortuneService" ref="fortuneService"/> |
||||
</lang:groovy> |
||||
---- |
||||
|
||||
[[dynamic-language-scenarios-validators]] |
||||
=== Scripted Validators |
||||
|
||||
Another area of application development with Spring that may benefit from the |
||||
flexibility afforded by dynamic-language-backed beans is that of validation. It can |
||||
be easier to express complex validation logic by using a loosely typed dynamic language |
||||
(that may also have support for inline regular expressions) as opposed to regular Java. |
||||
|
||||
Again, developing validators as dynamic-language-backed beans lets you change |
||||
validation logic by editing and saving a simple text file. Any such changes is |
||||
(depending on the configuration) automatically reflected in the execution of a |
||||
running application and would not require the restart of an application. |
||||
|
||||
NOTE: To effect the automatic "`pickup`" of any changes to dynamic-language-backed |
||||
beans, you have to enable the 'refreshable beans' feature. See |
||||
xref:languages/dynamic.adoc#dynamic-language-refreshable-beans[Refreshable Beans] |
||||
for a full and detailed treatment of this feature. |
||||
|
||||
The following example shows a Spring `org.springframework.validation.Validator` |
||||
implemented by using the Groovy dynamic language (see |
||||
xref:core/validation/validator.adoc[Validation using Spring’s Validator interface] |
||||
for a discussion of the `Validator` interface): |
||||
|
||||
[source,groovy,indent=0,subs="verbatim,quotes"] |
||||
---- |
||||
import org.springframework.validation.Validator |
||||
import org.springframework.validation.Errors |
||||
import org.springframework.beans.TestBean |
||||
|
||||
class TestBeanValidator implements Validator { |
||||
|
||||
boolean supports(Class clazz) { |
||||
return TestBean.class.isAssignableFrom(clazz) |
||||
} |
||||
|
||||
void validate(Object bean, Errors errors) { |
||||
if(bean.name?.trim()?.size() > 0) { |
||||
return |
||||
} |
||||
errors.reject("whitespace", "Cannot be composed wholly of whitespace.") |
||||
} |
||||
} |
||||
---- |
||||
|
||||
|
||||
[[dynamic-language-final-notes]] |
||||
== Additional Details |
||||
|
||||
This last section contains some additional details related to the dynamic language support. |
||||
|
||||
[[dynamic-language-final-notes-aop]] |
||||
=== AOP -- Advising Scripted Beans |
||||
|
||||
You can use the Spring AOP framework to advise scripted beans. The Spring AOP |
||||
framework actually is unaware that a bean that is being advised might be a scripted |
||||
bean, so all of the AOP use cases and functionality that you use (or aim to use) |
||||
work with scripted beans. When you advise scripted beans, you cannot use class-based |
||||
proxies. You must use xref:core/aop/proxying.adoc[interface-based proxies]. |
||||
|
||||
You are not limited to advising scripted beans. You can also write aspects themselves |
||||
in a supported dynamic language and use such beans to advise other Spring beans. |
||||
This really would be an advanced use of the dynamic language support though. |
||||
|
||||
[[dynamic-language-final-notes-scopes]] |
||||
=== Scoping |
||||
|
||||
In case it is not immediately obvious, scripted beans can be scoped in the same way as |
||||
any other bean. The `scope` attribute on the various `<lang:language/>` elements lets |
||||
you control the scope of the underlying scripted bean, as it does with a regular |
||||
bean. (The default scope is xref:core/beans/factory-scopes.adoc#beans-factory-scopes-singleton[singleton], |
||||
as it is with "`regular`" beans.) |
||||
|
||||
The following example uses the `scope` attribute to define a Groovy bean scoped as |
||||
a xref:core/beans/factory-scopes.adoc#beans-factory-scopes-prototype[prototype]: |
||||
|
||||
[source,xml,indent=0,subs="verbatim,quotes"] |
||||
---- |
||||
<?xml version="1.0" encoding="UTF-8"?> |
||||
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" |
||||
xmlns:lang="http://www.springframework.org/schema/lang" |
||||
xsi:schemaLocation=" |
||||
http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd |
||||
http://www.springframework.org/schema/lang https://www.springframework.org/schema/lang/spring-lang.xsd"> |
||||
|
||||
<lang:groovy id="messenger" script-source="classpath:Messenger.groovy" scope="prototype"> |
||||
<lang:property name="message" value="I Can Do The RoboCop" /> |
||||
</lang:groovy> |
||||
|
||||
<bean id="bookingService" class="x.y.DefaultBookingService"> |
||||
<property name="messenger" ref="messenger" /> |
||||
</bean> |
||||
|
||||
</beans> |
||||
---- |
||||
|
||||
See xref:core/beans/factory-scopes.adoc[Bean Scopes] in |
||||
xref:web/webmvc-view/mvc-xslt.adoc#mvc-view-xslt-beandefs[The IoC Container] |
||||
for a full discussion of the scoping support in the Spring Framework. |
||||
|
||||
[[xsd-schemas-lang]] |
||||
=== The `lang` XML schema |
||||
|
||||
The `lang` elements in Spring XML configuration deal with exposing objects that have been |
||||
written in a dynamic language (such as Groovy or BeanShell) as beans in the Spring container. |
||||
|
||||
These elements (and the dynamic language support) are comprehensively covered in |
||||
xref:languages/dynamic.adoc[Dynamic Language Support]. See that section |
||||
for full details on this support and the `lang` elements. |
||||
|
||||
To use the elements in the `lang` schema, you need to have the following preamble at the |
||||
top of your Spring XML configuration file. The text in the following snippet references |
||||
the correct schema so that the tags in the `lang` namespace are available to you: |
||||
|
||||
[source,xml,indent=0,subs="verbatim,quotes"] |
||||
---- |
||||
<?xml version="1.0" encoding="UTF-8"?> |
||||
<beans xmlns="http://www.springframework.org/schema/beans" |
||||
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" |
||||
xmlns:lang="http://www.springframework.org/schema/lang" |
||||
xsi:schemaLocation=" |
||||
http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd |
||||
http://www.springframework.org/schema/lang https://www.springframework.org/schema/lang/spring-lang.xsd"> |
||||
|
||||
<!-- bean definitions here --> |
||||
|
||||
</beans> |
||||
---- |
||||
|
||||
|
||||
[[dynamic-language-resources]] |
||||
== Further Resources |
||||
|
||||
The following links go to further resources about the various dynamic languages referenced |
||||
in this chapter: |
||||
|
||||
* The https://www.groovy-lang.org/[Groovy] homepage |
||||
* The https://beanshell.github.io/intro.html[BeanShell] homepage |
||||
* The https://www.jruby.org[JRuby] homepage |
||||
Loading…
Reference in new issue