Cglib动态代理详解

2023-08-20 微信公众号程序员长承

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CGLIB 简介

为没有实现接口的类提供代理
更好的性能

CGLIB 原理

原理：动态生成需要代理的子类，子类重写代理类的非final方法。子类中采用方法拦截的奇数拦截所有父类的方法的调用，顺势织入横切逻辑。
底层：使用ASM字节码处理框架。
缺点：无法代理fianl方法。

CGLIB 应用

Spring AOP

CGLIB API

.NET.sf.cglib.core: 底层字节码处理类，他们大部分与ASM有关系。
net.sf.cglib.transform: 编译期或运行期类和类文件的转换
net.sf.cglib.proxy: 实现创建代理和方法拦截器的类
net.sf.cglib.reflect: 实现快速反射和C#风格代理的类
net.sf.cglib.util: 集合排序等工具类
net.sf.cglib.beans: JAVABean相关的工具类

Code Example

Basic

package com.cclu.cglibproxy;
import java.util.HashMap;import java.util.Map;
/** * @author ChangCheng Lu * @date 2023/8/20 15:59 */public class UserService {
    private static final Map<String, String> nameMap;
    private static final Map<String, String> addressMap;
    static {        nameMap = new HashMap<>(3);        nameMap.put("1001", "木子");        nameMap.put("1002", "小一");        nameMap.put("1003", "阿同");
        addressMap = new HashMap<>(3);        addressMap.put("1001", "涟水");        addressMap.put("1002", "淮安");        addressMap.put("1003", "上海");    }
    public String getUserNameById(String userId) {        return nameMap.get(userId);    }
    public String getAddressById(String userId) {        return addressMap.get(userId);    }
}

package com.cclu.cglibproxy;
import net.sf.cglib.proxy.MethodInterceptor;import net.sf.cglib.proxy.MethodProxy;
import java.lang.reflect.Method;
/** * @author ChangCheng Lu * @date 2023/8/20 16:04 */public class LogInterceptor implements MethodInterceptor {    @Override    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {        System.out.println("方法调用前...");        Object res = methodProxy.invokeSuper(o, objects);        System.out.println("方法调用后："+res);        return res;    }}

package com.cclu.cglibproxy;
import net.sf.cglib.proxy.Enhancer;
/** * @author ChangCheng Lu * @date 2023/8/20 16:10 */public class Client {    public static void mAIn(String[] args) {        Enhancer enhancer = new Enhancer();        enhancer.setSuperclass(UserService.class);        enhancer.setCallback(new LogInterceptor());        UserService userService = (UserService) enhancer.create();        userService.getUserNameById("1001");        userService.getAddressById("1003");    }}

Filter、FixedValue

package com.cclu.cglibproxy;
import java.util.HashMap;import java.util.Map;
/** * @author ChangCheng Lu * @date 2023/8/20 15:59 */public class UserService {
    private static final Map<String, String> nameMap;
    private static final Map<String, String> addressMap;
    static {        nameMap = new HashMap<>(3);        nameMap.put("1001", "木子");        nameMap.put("1002", "小一");        nameMap.put("1003", "阿同");
        addressMap = new HashMap<>(3);        addressMap.put("1001", "苏州");        addressMap.put("1002", "淮安");        addressMap.put("1003", "上海");    }
    public String getUserNameById(String userId) {        return nameMap.get(userId);    }
    public String getAddressById(String userId) {        return addressMap.get(userId);    }
}

package com.cclu.cglibproxy;
import net.sf.cglib.proxy.CallbackFilter;
import java.lang.reflect.Method;
/** * @author ChangCheng Lu * @date 2023/8/20 16:35 */public class LogInterceptorFilter implements CallbackFilter {    @Override    public int accept(Method method) {        if (method.getName().equals("getUserNameById")) {            System.out.println("是不是木子？");            return 1;        } else if (method.getName().equals("getAddressById")) {            System.out.println("是不是阿同？");            return 2;        }        return 0;    }}

package com.cclu.cglibproxy;
import net.sf.cglib.proxy.FixedValue;
/** * @author ChangCheng Lu * @date 2023/8/20 17:44 */public class TargetResultFixed implements FixedValue {    @Override    public Object loadObject() throws Exception {        System.out.println("锁定结果");        Object obj = "苏州";        return obj;    }}

package com.cclu.cglibproxy;
import net.sf.cglib.proxy.Callback;import net.sf.cglib.proxy.Enhancer;import net.sf.cglib.proxy.NoOp;import org.junit.Test;
/** * @author ChangCheng Lu * @date 2023/8/20 17:32 */public class ProxyTest {
    @Test    public void filterTest() {        Enhancer enhancer = new Enhancer();        enhancer.setSuperclass(UserService.class);        enhancer.setCallbackFilter(new LogInterceptorFilter());        enhancer.setCallbacks(new Callback[]{NoOp.INSTANCE, new LogInterceptor(), new TargetResultFixed()});
        UserService userService = (UserService) enhancer.create();        System.out.println(userService);        System.out.println(userService.getUserNameById("1001"));        System.out.println(userService.getAddressById("1003"));    }
}

参考文档

https://www.runoob.com/w3cnote/cglibcode-generation-library-intro.html