Enhance Groovy template support in CLI

to allow user to specify the TemplateEngine

Fixes gh-908

spring-boot-cli/samples/template.groovy

@@ -8,6 +8,7 @@ class Example implements CommandLineRunner {
 	@Autowired
 	private MyService myService
 
+	@Override
 	void run(String... args) {
 		print template("test.txt", ["message":myService.sayWorld()])
 	}

spring-boot-cli/src/main/java/org/springframework/boot/cli/compiler/autoconfigure/SpringMvcCompilerAutoConfiguration.java

@@ -51,7 +51,7 @@ public class SpringMvcCompilerAutoConfiguration extends CompilerAutoConfiguratio
 				"org.springframework.web.servlet.config.annotation",
 				"org.springframework.web.servlet",
 				"org.springframework.web.servlet.handler", "org.springframework.http",
-				"org.springframework.ui");
+				"org.springframework.ui", "groovy.text");
 		imports.addStaticImport(GroovyTemplate.class.getName(), "template");
 	}
 

spring-boot-cli/src/main/java/org/springframework/boot/groovy/GroovyTemplate.java

@@ -16,11 +16,14 @@
 
 package org.springframework.boot.groovy;
 
+import groovy.lang.Writable;
 import groovy.text.GStringTemplateEngine;
 import groovy.text.Template;
+import groovy.text.TemplateEngine;
 
 import java.io.File;
 import java.io.IOException;
+import java.io.StringWriter;
 import java.net.URL;
 import java.util.Collections;
 import java.util.Map;
@@ -41,7 +44,15 @@ public abstract class GroovyTemplate {
 
 	public static String template(String name, Map<String, ?> model) throws IOException,
 			CompilationFailedException, ClassNotFoundException {
-		return getTemplate(name).make(model).toString();
+		return template(new GStringTemplateEngine(), name, model);
+	}
+
+	public static String template(TemplateEngine engine, String name, Map<String, ?> model)
+			throws IOException, CompilationFailedException, ClassNotFoundException {
+		Writable writable = getTemplate(name).make(model);
+		StringWriter result = new StringWriter();
+		writable.writeTo(result);
+		return result.toString();
 	}
 
 	private static Template getTemplate(String name) throws CompilationFailedException,