动态生成class

动态生成class

ASM 进行动态生成class

import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

public class HelloWorld extends ClassLoader implements Opcodes{
	public static void main(String[] args) {
		ClassWriter cw = new ClassWriter(0);
		cw.visit(V1_1, ACC_PUBLIC, "Example", null, "java/lang/Object", null);
		MethodVisitor mw = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
		mw.visitVarInsn(ALOAD, 0);
		mw.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V");
		mw.visitInsn(RETURN);
		mw.visitMaxs(1, 1);
		mw.visitEnd();
		
		mw = cw.visitMethod(ACC_PUBLIC+ACC_STATIC, "main", "([Ljava/lang/String;)V", null, null);
		mw.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
		mw.visitLdcInsn("Hello World!");
		mw.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V");
		mw.visitInsn(RETURN);
		mw.visitMaxs(2, 2);
		mw.visitEnd(); 
		
		byte[] code = cw.toByteArray();
		FileOutputStream fos;
		try {
			fos = new FileOutputStream("Example.class");
			fos.write(code);
			fos.close();
			
			HelloWorld loader = new HelloWorld();   
		     Class exampleClass = loader   
		         .defineClass("Example", code, 0, code.length);  
				exampleClass.getMethods()[0].invoke(null, new Object[] { null });
				
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalArgumentException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SecurityException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (InvocationTargetException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
		
	}
}

 

cglib 动态生成class 并进行拦截

 

public class MyClass {
	public void print() {
		System.out.println("I'm in MyClass.print!");
	}
}


import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;

public class Main {

	public static void main(String[] args) {

		Enhancer enhancer = new Enhancer();
		enhancer.setSuperclass(MyClass.class);
		enhancer.setCallback((Callback) new MethodInterceptorImpl());
		MyClass my = (MyClass) enhancer.create();
		my.print();
	}

	private static class MethodInterceptorImpl implements MethodInterceptor {

		public Object intercept(Object obj, Method method, Object[] args,
				MethodProxy proxy) throws Throwable {
			// log something
			System.out.println(method + " intercepted!");

			proxy.invokeSuper(obj, args);
			return null;
		}

	}
}

 

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