使用ASM动态创建接口实现类

使用ASM动态生成一个接口的实现类，接口如下：

public interface ISayHello {
	public void MethodA();
	public void MethodB();
	public void Abs();
}

 具体实现如下：

public class InterfaceHandler extends ClassLoader implements Opcodes {
	public static Object MakeClass(Class<?> clazz) throws Exception {
		String name = clazz.getSimpleName();
		String className = name + "$imp";

		String Iter = clazz.getName().replaceAll("\.", "/");

		ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
		cw.visit(V1_5, ACC_PUBLIC + ACC_SUPER, className, null,
				"java/lang/Object", new String[] { Iter });

		// 空构造
		MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null,
				null);
		mv.visitVarInsn(ALOAD, 0);
		mv.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V");
		mv.visitInsn(RETURN);
		mv.visitMaxs(1, 1);
		mv.visitEnd();

		// 实现接口中所有方法
		Method[] methods = clazz.getMethods();
		for (Method method : methods) {
			MakeMethod(cw, method.getName(), className);
		}
		cw.visitEnd();
		
		//写入文件
		byte[] code = cw.toByteArray();
		FileOutputStream fos = new FileOutputStream("d:/com/" + className + ".class");
		fos.write(code);
		fos.close();

		//从文件加载类
		InterfaceHandler loader = new InterfaceHandler();
		Class<?> exampleClass = loader.defineClass(className, code, 0,
				code.length);

		Object obj = exampleClass.getConstructor().newInstance();
		return obj;
	}

	private static void MakeMethod(ClassWriter cw, String MethodName,
			String className) {
		MethodVisitor mv = cw.visitMethod(ACC_PUBLIC, MethodName, "()V", null, null);
		//mv.visitCode();
		//Label l0 = new Label();
		//mv.visitLabel(l0);
		//mv.visitLineNumber(8, l0);
		mv.visitFieldInsn(GETSTATIC, "java/lang/System", "out",
				"Ljava/io/PrintStream;");
		mv.visitLdcInsn("调用方法 [" + MethodName + "]");
		mv.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println",
				"(Ljava/lang/String;)V");
		//Label l1 = new Label();
		//mv.visitLabel(l1);
		//mv.visitLineNumber(9, l1);
		mv.visitInsn(RETURN);
		//Label l2 = new Label();
		//mv.visitLabel(l2);
		//mv.visitLocalVariable("this", "L" + className + ";", null, l0, l2, 0);
		mv.visitMaxs(2, 1);
		mv.visitEnd();
	}
	public static void main(final String args[]) throws Exception {
		ISayHello iSayHello = (ISayHello) MakeClass(ISayHello.class);
		iSayHello.MethodA();
		iSayHello.MethodB();
		iSayHello.Abs();
	}
}

 注意，使用ASM访问属性和方法的时候，会返回一个Visitor对象，如属性为FieldVisitor，方法为MethodVisitor。

 使用反编译工具查看生成的字节码文件内容如下：

public class ISayHello$imp
  implements ISayHello
{
  public void MethodA()
  {
    System.out.println("调用方法 [MethodA]");
  }

  public void MethodB()
  {
    System.out.println("调用方法 [MethodB]");
  }

  public void Abs()
  {
    System.out.println("调用方法 [Abs]");
  }
}