Spring 高级 jdk代理原理-源码篇

一、利用Arthas工具 反编译出源码

发现和我们自己写的模拟jdk代理差不多

/*
 * Decompiled with CFR.
 *
 * Could not load the following classes:
 *  com.mangoubiubiu.show.a12.JdkProxyDemo$Foo
 */
package com.mangoubiubiu.show.a12;

import com.mangoubiubiu.show.a12.JdkProxyDemo;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

final class $Proxy0 extends Proxy implements JdkProxyDemo.Foo {
    private static Method m1;
    private static Method m2;
    private static Method m3;
    private static Method m0;

    public $Proxy0(InvocationHandler invocationHandler) {
        super(invocationHandler);
    }

    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
            m3 = Class.forName("com.mangoubiubiu.show.a12.JdkProxyDemo$Foo").getMethod("foo", new Class[0]);
            m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
            return;
        }
        catch (NoSuchMethodException noSuchMethodException) {
            throw new NoSuchMethodError(noSuchMethodException.getMessage());
        }
        catch (ClassNotFoundException classNotFoundException) {
            throw new NoClassDefFoundError(classNotFoundException.getMessage());
        }
    }

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

    public final String toString() {
        try {
            return (String)this.h.invoke(this, m2, null);
        }
        catch (Error | RuntimeException throwable) {
            throw throwable;
        }
        catch (Throwable throwable) {
            throw new UndeclaredThrowableException(throwable);
        }
    }

    public final int hashCode() {
        try {
            return (Integer)this.h.invoke(this, m0, null);
        }
        catch (Error | RuntimeException throwable) {
            throw throwable;
        }
        catch (Throwable throwable) {
            throw new UndeclaredThrowableException(throwable);
        }
    }

    public final void foo() {
        try {
            this.h.invoke(this, m3, null);
            return;
        }
        catch (Error | RuntimeException throwable) {
            throw throwable;
        }
        catch (Throwable throwable) {
            throw new UndeclaredThrowableException(throwable);
        }
    }
}

收获💡

代理一点都不难，无非就是利用了多态、反射的知识

1. 方法重写可以增强逻辑，只不过这【增强逻辑】千变万化，不能写死在代理内部
2. 通过接口回调将【增强逻辑】置于代理类之外
3. 配合接口方法反射（是多态调用），就可以再联动调用目标方法
4. 会用 arthas 的 jad 工具反编译代理类
5. 限制⛔：代理增强是借助多态来实现，因此成员变量、静态方法、final 方法均不能通过代理实现