java proxy原理

準備測試環境

public interface UserService {
    void save(String name);
}

@Slf4j
public class UserServiceImpl implements UserService {
    @Override
    public void save(String name) {
        log.info("hello, {}", name);
    }
}

@Slf4j
public class ProxyTest {

    @Before
    public void before() {
        System.setProperty("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
    }

    @Test
    public void testMethodInvoke() {
        final UserService userService = new UserServiceImpl();
        UserService proxyUserService = (UserService) Proxy.newProxyInstance(UserService.class.getClassLoader(),
                new Class[]{UserService.class}, (proxy, method, methodArgs) -> {
                    if (Object.class.equals(method.getDeclaringClass()))
                        log.info("before user save");
                    return method.invoke(userService, methodArgs);
                });

        proxyUserService.save("uc");

    }
}

生成代碼

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.sun.proxy;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
import me.uc.proxy.UserService;

public final class $Proxy0 extends Proxy implements UserService {
    private static Method m1;
    private static Method m3;
    private static Method m2;
    private static Method m0;

    public $Proxy0(InvocationHandler var1) throws  {
    　// var1 在構建時傳入
        super(var1);
    }

    public final boolean equals(Object var1) throws  {
        try {
            return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final void save(String var1) throws  {
        try {
            super.h.invoke(this, m3, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final String toString() throws  {
        try {
            return (String)super.h.invoke(this, m2, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final int hashCode() throws  {
        try {
            return (Integer)super.h.invoke(this, m0, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m3 = Class.forName("me.uc.proxy.UserService").getMethod("save", Class.forName("java.lang.String"));
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

分析

Proxy.newProxyInstance　返回的是$Proxy0的實例，所有的方法都會調用InvocationHandler