cglib 指南

最新推荐文章于 2024-08-09 08:04:57 发布

转载最新推荐文章于 2024-08-09 08:04:57 发布 · 1.5k 阅读

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#import #class #object #delegates #system #callback

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本文介绍了Cglib（CodeGenerationLibrary）的基本概念及其在Java动态代理中的应用。通过具体的代码示例展示了如何使用Cglib增强现有类的功能，包括基本的动态代理实现、使用CallbackFilter进行方法拦截的选择性配置，以及利用Mixin实现多个接口的方法。

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cglib，全称是Code Generation Library，它可以用来动态继承Java类或者实现接口，很多知名的开源项目中用到了它，譬如Hibernate，Spring之类用它来实现动态代理。

增强一个已有类

public class MyClass {
 
	public void method() {
		System.out.println("MyClass.method()");
	}
}

import java.lang.reflect.Method;
 
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodProxy;
import net.sf.cglib.proxy.MethodInterceptor;
 
public class Main {
 
	public static void main(String[] args) {
 
		Enhancer enhancer = new Enhancer();
 
		enhancer.setSuperclass(MyClass.class);
		enhancer.setCallback( new MethodInterceptorImpl() );
 
 
		MyClass my = (MyClass)enhancer.create();
 
		my.method();
	}
 
	private static class MethodInterceptorImpl implements MethodInterceptor {
		
		public Object intercept(Object obj, 
                                Method method, 
                                Object[] args, 
                                MethodProxy proxy) throws Throwable {
 
			System.out.println(method);
 
			proxy.invokeSuper(obj, args);
 
			return null;
		}
	}
}

执行结果：

public void cglib_test.MyClass.method()
MyClass.method()

使用CallbackFilter

public class MyClass {
 
	public void method() {
		System.out.println("MyClass.method()");
	}
 
	public void method2() {
		System.out.println("MyClass.method2()");
	}
}

import java.lang.reflect.Method;
 
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodProxy;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.NoOp;
import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.CallbackFilter;
 
 
public class Main {
 
	public static void main(String[] args) {
 
		Callback[] callbacks =
			new Callback[] { new MethodInterceptorImpl(),  NoOp.INSTANCE };
 
		Enhancer enhancer = new Enhancer();
 
		enhancer.setSuperclass(MyClass.class);
		enhancer.setCallbacks( callbacks );
		enhancer.setCallbackFilter( new CallbackFilterImpl() );
 
 
		MyClass my = (MyClass)enhancer.create();
 
		my.method();
		my.method2();
	}
 
	private static class CallbackFilterImpl implements CallbackFilter {
 
		public int accept(Method method) {
 
			if ( method.getName().equals("method2") ) {
				return 1;
 
			} else {
				return 0;
			}
		}
	}
 
	private static class MethodInterceptorImpl implements MethodInterceptor {
		
		public Object intercept(Object obj, 
                                Method method, 
                                Object[] args, 
                                MethodProxy proxy) throws Throwable {
 
			System.out.println(method);
 
			return proxy.invokeSuper(obj, args);
		}
	}
}

执行结果：

public void cglib_test.MyClass.method()
MyClass.method()
MyClass.method2()

使用Mixin

public interface MyInterfaceA {
 
	public void methodA();
}
 
public interface  MyInterfaceB {
	public void methodB();
}
 
public class MyInterfaceAImpl implements MyInterfaceA {
 
	public void methodA() {
		System.out.println("MyInterfaceAImpl.methodA()");
	}
}
 
public class MyInterfaceBImpl implements MyInterfaceB {
 
	public void methodB() {
		System.out.println("MyInterfaceBImpl.methodB()");
	}
}

import net.sf.cglib.proxy.Mixin;
 
public class Main {
 
	public static void main(String[] args) {
 
		Class[] interfaces =
			new Class[] { MyInterfaceA.class, MyInterfaceB.class };
		
		Object[] delegates =
			new Object[] { new MyInterfaceAImpl(), new MyInterfaceBImpl() };
			
		
		Object obj = Mixin.create(interfaces, delegates);
 
 
		MyInterfaceA myA = (MyInterfaceA)obj;
		myA.methodA();
 
 
		MyInterfaceB myB = (MyInterfaceB)obj;
		myB.methodB();
	}
}

执行结果：

MyInterfaceAImpl.methodA()
MyInterfaceBImpl.methodB()