Detect default value from factory method

If a field is initialized via a factory method taking a single argument,
we can relatively safely consider that said argument is a good
representation of its default value. This is typically the case for
Charset or MimeType instances.

We now make sure to detect such use case (i.e. method argument with a
single argument).

Closes gh-3482

spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/fieldvalues/javac/ExpressionTree.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2014 the original author or authors.
+ * Copyright 2012-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -24,6 +24,7 @@ import java.util.List;
  * Reflection based access to {@code com.sun.source.tree.ExpressionTree}.
  *
  * @author Phillip Webb
+ * @author Stephane Nicoll
  * @since 1.2.0
  */
 class ExpressionTree extends ReflectionWrapper {
@@ -32,6 +33,10 @@ class ExpressionTree extends ReflectionWrapper {
 
 	private final Method literalValueMethod = findMethod(this.literalTreeType, "getValue");
 
+	private final Class<?> methodInvocationTreeType = findClass("com.sun.source.tree.MethodInvocationTree");
+
+	private final Method methodInvocationArgumentsMethod = findMethod(this.methodInvocationTreeType, "getArguments");
+
 	private final Class<?> newArrayTreeType = findClass("com.sun.source.tree.NewArrayTree");
 
 	private final Method arrayValueMethod = findMethod(this.newArrayTreeType,
@@ -52,6 +57,16 @@ class ExpressionTree extends ReflectionWrapper {
 		return null;
 	}
 
+	public Object getFactoryValue() throws Exception {
+		if (this.methodInvocationTreeType.isAssignableFrom(getInstance().getClass())) {
+			List<?> arguments = (List<?>) this.methodInvocationArgumentsMethod.invoke(getInstance());
+			if (arguments.size() == 1) {
+				return new ExpressionTree(arguments.get(0)).getLiteralValue();
+			}
+		}
+		return null;
+	}
+
 	public List<? extends ExpressionTree> getArrayExpression() throws Exception {
 		if (this.newArrayTreeType.isAssignableFrom(getInstance().getClass())) {
 			List<?> elements = (List<?>) this.arrayValueMethod.invoke(getInstance());

spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/fieldvalues/javac/JavaCompilerFieldValuesParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2014 the original author or authors.
+ * Copyright 2012-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -32,6 +32,7 @@ import org.springframework.boot.configurationprocessor.fieldvalues.FieldValuesPa
  * {@link FieldValuesParser} implementation for the standard Java compiler.
  *
  * @author Phillip Webb
+ * @author Stephane Nicoll
  * @since 1.2.0
  */
 public class JavaCompilerFieldValuesParser implements FieldValuesParser {
@@ -121,6 +122,10 @@ public class JavaCompilerFieldValuesParser implements FieldValuesParser {
 			if (literalValue != null) {
 				return literalValue;
 			}
+			Object factoryValue = expression.getFactoryValue();
+			if (factoryValue != null) {
+				return factoryValue;
+			}
 			List<? extends ExpressionTree> arrayValues = expression.getArrayExpression();
 			if (arrayValues != null) {
 				Object[] result = new Object[arrayValues.size()];

spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/fieldvalues/AbstractFieldValuesProcessorTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2014 the original author or authors.
+ * Copyright 2012-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -74,6 +74,10 @@ public abstract class AbstractFieldValuesProcessorTests {
 		assertThat(values.get("integerObject"), equalToObject(3));
 		assertThat(values.get("integerObjectNone"), nullValue());
 		assertThat(values.get("integerObjectConst"), equalToObject(4));
+		assertThat(values.get("charset"), equalToObject("US-ASCII"));
+		assertThat(values.get("charsetConst"), equalToObject("UTF-8"));
+		assertThat(values.get("mimeType"), equalToObject("text/html"));
+		assertThat(values.get("mimeTypeConst"), equalToObject("text/plain"));
 		assertThat(values.get("object"), equalToObject(123));
 		assertThat(values.get("objectNone"), nullValue());
 		assertThat(values.get("objectConst"), equalToObject("c"));

spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationsample/fieldvalues/FieldValues.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2014 the original author or authors.
+ * Copyright 2012-2015 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,7 +16,10 @@
 
 package org.springframework.boot.configurationsample.fieldvalues;
 
+import java.nio.charset.Charset;
+
 import org.springframework.boot.configurationsample.ConfigurationProperties;
+import org.springframework.util.MimeType;
 
 /**
  * Sample object containing fields with initial values.
@@ -38,6 +41,10 @@ public class FieldValues {
 
 	private static final Integer INTEGER_OBJ_CONST = 4;
 
+	private static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");
+
+	private static final MimeType DEFAULT_MIME_TYPE = MimeType.valueOf("text/plain");
+
 	private static final String[] STRING_ARRAY_CONST = new String[] { "OK", "KO" };
 
 	private String string = "1";
@@ -70,6 +77,14 @@ public class FieldValues {
 
 	private Integer integerObjectConst = INTEGER_OBJ_CONST;
 
+	private Charset charset = Charset.forName("US-ASCII");
+
+	private Charset charsetConst = DEFAULT_CHARSET;
+
+	private MimeType mimeType = MimeType.valueOf("text/html");
+
+	private MimeType mimeTypeConst = DEFAULT_MIME_TYPE;
+
 	private Object object = 123;
 
 	private Object objectNone;