Jdk6中的源代码编译功能

JDK6中的源代码编译功能，网上给的示例一般都无法运行，会抛出ClassNotFoundException。
经过改良，主要原因是字节码输出的文件不对。现修改为输出到内存中。

/**
 * 字符串变为Class
 * 
 * @author wuyuhou
 * 
 */
public class StringToClass {
	
	public static void main(String[] args) throws Exception {
		Class clazz = loadClass("com.test.CalculatorTest", 
				"package com.test;"
				+ "public class CalculatorTest {"
				+ "   public int multiply(int multiplicand, int multiplier) {" 
				+ "     System.out.print(multiplicand + \" * \");" 
				+ "     System.out.print(multiplier + \" = \");"
				+ "     return multiplicand * multiplier;" 
				+ "   }" 
				+ "}", StringToClass.class.getClassLoader());
		Object instance = clazz.newInstance();
		Method m = clazz.getMethod("multiply", new Class[] {
				int.class, int.class
		});
		Object[] o = new Object[] {
				3, 2
		};
		System.out.println(m.invoke(instance, o));
	}

	public static Class loadClass(String className, String javaSource, ClassLoader loader) throws ClassNotFoundException {
		JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
		//源码Java对象
		JavaFileObject sourceFileObject = new SimpleJavaFileObjectWrapper(className, Kind.SOURCE, javaSource, null);
		
		//输出到内存中
		ByteArrayOutputStream byteArrayOutput = new ByteArrayOutputStream();
		//Class输出Java对象
		JavaFileObject outputFileObject = new SimpleJavaFileObjectWrapper(className, Kind.CLASS, null, byteArrayOutput);
		
		Iterable<JavaFileObject> files = Arrays.asList(sourceFileObject);
		StandardJavaFileManager fileManager = new StandardJavaFileManagerWrapper(compiler.getStandardFileManager(null, null, null), outputFileObject);
		JavaCompiler.CompilationTask task = compiler.getTask(null, fileManager, null, null, null, files);
		task.call();
		//字节码数组
		byte[] classBytes = byteArrayOutput.toByteArray();
		return new SimpleClassLoader(loader).loadClass(classBytes);
	}
	
	private static class SimpleClassLoader extends ClassLoader {
		public SimpleClassLoader(ClassLoader parent) {
			super(parent);
		}
		public Class<?> loadClass(byte[] classBytes) throws ClassNotFoundException {
			return defineClass(null, classBytes, 0, classBytes.length);
		}
	}
	
	private static class SimpleJavaFileObjectWrapper extends SimpleJavaFileObject {
		
		private String javaSource = null;
		private ByteArrayOutputStream byteArrayOutput = null;
		public SimpleJavaFileObjectWrapper(String className, Kind kind, String javaSource, ByteArrayOutputStream byteArrayOutput) {
			super(URI.create("string:///" + className.replace('.', '/') + kind.extension), kind);
			this.javaSource = javaSource;
			this.byteArrayOutput = byteArrayOutput;
		}
		
		@Override
		public CharSequence getCharContent(boolean ignoreEncodingErrors) throws IOException {
			return javaSource;
		}
		
		@Override
		public OutputStream openOutputStream() throws IOException {
			return byteArrayOutput;
		}
	}

	private static class StandardJavaFileManagerWrapper implements StandardJavaFileManager {
		private StandardJavaFileManager defaultWrapper = null;

		private JavaFileObject outputFileObject = null;

		public StandardJavaFileManagerWrapper(StandardJavaFileManager defaultWrapper, JavaFileObject outputFileObject) {
			this.defaultWrapper = defaultWrapper;
			this.outputFileObject = outputFileObject;
		}

		public ClassLoader getClassLoader(Location location) {
			return defaultWrapper.getClassLoader(location);
		}

		public Iterable<JavaFileObject> list(Location location, String packageName, Set<Kind> kinds, boolean recurse) throws IOException {
			return defaultWrapper.list(location, packageName, kinds, recurse);
		}

		public String inferBinaryName(Location location, JavaFileObject file) {
			return defaultWrapper.inferBinaryName(location, file);
		}

		public boolean handleOption(String current, Iterator<String> remaining) {
			return defaultWrapper.handleOption(current, remaining);
		}

		public boolean hasLocation(Location location) {
			return defaultWrapper.hasLocation(location);
		}

		public JavaFileObject getJavaFileForInput(Location location, String className, Kind kind) throws IOException {
			return defaultWrapper.getJavaFileForInput(location, className, kind);
		}

		// 输出重新定位，否则就会报出ClassNotFoundException
		public JavaFileObject getJavaFileForOutput(Location location, String className, Kind kind, FileObject sibling) throws IOException {
			if (outputFileObject != null) {
				return outputFileObject;
			}
			return defaultWrapper.getJavaFileForOutput(location, className, kind, sibling);
		}

		public FileObject getFileForInput(Location location, String packageName, String relativeName) throws IOException {
			return defaultWrapper.getFileForInput(location, packageName, relativeName);
		}

		public FileObject getFileForOutput(Location location, String packageName, String relativeName, FileObject sibling) throws IOException {
			return defaultWrapper.getFileForOutput(location, packageName, relativeName, sibling);
		}

		public void flush() throws IOException {
			defaultWrapper.flush();
		}

		public void close() throws IOException {
			defaultWrapper.close();
		}

		public int isSupportedOption(String option) {
			return defaultWrapper.isSupportedOption(option);
		}

		public boolean isSameFile(FileObject a, FileObject b) {
			return defaultWrapper.isSameFile(a, b);
		}

		public Iterable<? extends JavaFileObject> getJavaFileObjectsFromFiles(Iterable<? extends File> files) {
			return defaultWrapper.getJavaFileObjectsFromFiles(files);
		}

		public Iterable<? extends JavaFileObject> getJavaFileObjects(File... files) {
			return defaultWrapper.getJavaFileObjects(files);
		}

		public Iterable<? extends JavaFileObject> getJavaFileObjectsFromStrings(Iterable<String> names) {
			return defaultWrapper.getJavaFileObjectsFromStrings(names);
		}

		public Iterable<? extends JavaFileObject> getJavaFileObjects(String... names) {
			return defaultWrapper.getJavaFileObjects(names);
		}

		public void setLocation(Location location, Iterable<? extends File> path) throws IOException {
			defaultWrapper.setLocation(location, path);
		}

		public Iterable<? extends File> getLocation(Location location) {
			return defaultWrapper.getLocation(location);
		}
	}
}