深度剖析java动态静态代理原理源码

/**
* 创建Person接口
* @author ChenHao
*/
public interface Person {
//上交班费
void giveMoney();
}

public class Student implements Person {
private String name;
public Student(String name) {
this.name = name;
}
@Override
public void giveMoney() {
System.out.println(name + "上交班费50元");
}
}

/**
* 学生代理类，也实现了Person接口，保存一个学生实体，这样既可以代理学生产生行为
* @author ChenHao
*
*/
public class StudentsProxy implements Person{
//被代理的学生
Student stu;
public StudentsProxy(Student stu) {
this.stu = stu;
}
//代理上交班费，调用被代理学生的上交班费行为
public void giveMoney() {
stu.giveMoney();
}
}

public class StaticProxyTest {
public static void main(String[] args) {
//被代理的学生张三，他的班费上交有代理对象monitor（班长）完成
Student zhangsan = new Student("张三");
//生成代理对象，并将张三传给代理对象
Person monitor = new StudentsProxy(zhangsan);
//班长代理上交班费
monitor.giveMoney();
}
}

/**
* 学生代理类，也实现了Person接口，保存一个学生实体，这样既可以代理学生产生行为
* @author ChenHao
*
*/
public class StudentsProxy implements Person{
//被代理的学生
Student stu;
public StudentsProxy(Student stu) {
this.stu = stu;
}
//代理上交班费，调用被代理学生的上交班费行为
public void giveMoney() {
System.out.println("张三最近学习有进步！");
stu.giveMoney();
}
}

public class DynamicProxyTest {
interface IHello {
void sayHello();
}
static class Hello implements IHello {
@Override
public void sayHello() {
System.out.println("hello world");
}
}
static class DynamicProxy implements InvocationHandler {
Object originalObj;
Object bind(Object originalObj) {
this.originalObj = originalObj;
return Proxy.newProxyInstance(originalObj.getClass().getClassLoader(), originalObj.getClass().getInterfaces(), this);
}
/**
*Object proxy是代理的对象, Method method是真实对象中调用方法的Method类, Object[] args是真实对象中调用方法的参数
*/
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("welcome");
return method.invoke(originalObj, args);
}
}
public static void main(String[] args) {
IHello hello = (IHello) new DynamicProxy().bind(new Hello());
hello.sayHello();
}
}

welcome 
hello world

public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h) throws IllegalArgumentException {
　　// handler不能为空
if (h == null) {
throw new NullPointerException();
}
final Class<?>[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
/*
* Look up or generate the designated proxy class.
*/
　　// 通过loader和接口，得到代理的Class对象
Class<?> cl = getProxyClass0(loader, intfs);

/*
* Invoke its constructor with the designated invocation handler.
*/
try {
final Constructor<?> cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
if (sm != null && ProxyAccessHelper.needsNewInstanceCheck(cl)) {
// create proxy instance with doPrivilege as the proxy class may
// implement non-public interfaces that requires a special permission
return AccessController.doPrivileged(new PrivilegedAction<Object>() {
public Object run() {
return newInstance(cons, ih);
}
});
} else {
　　　　　　　// 创建代理对象的实例
return newInstance(cons, ih);
}
} catch (NoSuchMethodException e) {
throw new InternalError(e.toString());
}
}

private static Object newInstance(Constructor<?> cons, InvocationHandler h) {
try {
return cons.newInstance(new Object[] {h} );
} catch (IllegalAccessException | InstantiationException e) {
throw new InternalError(e.toString());
} catch (InvocationTargetException e) {
Throwable t = e.getCause();
if (t instanceof RuntimeException) {
throw (RuntimeException) t;
} else {
throw new InternalError(t.toString());
}
}
}

/**
* 代理类的生成工具 
* @author ChenHao
* @since 2019-4-2 
*/
public class ProxyGeneratorUtils {
/**
* 把代理类的字节码写到硬盘上 
* @param path 保存路径 
*/
public static void writeProxyClassToHardDisk(String path) {
// 第一种方法
// System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", true); 
// 第二种方法 
// 获取代理类的字节码 
byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy11", UserServiceImpl.class.getInterfaces());
FileOutputStream out = null;
try {
out = new FileOutputStream(path);
out.write(classFile);
out.flush();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
ProxyGeneratorUtils.writeProxyClassToHardDisk("C:/x/$Proxy11.class");
}
} 

package org.fenixsoft.bytecode;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
public final class $Proxy0 extends Proxy
implements DynamicProxyTest.IHello
{
private static Method m3;
private static Method m1;
private static Method m0;
private static Method m2;
/**
*注意这里是生成代理类的构造方法，方法参数为InvocationHandler类型，看到这，是不是就有点明白
*super(paramInvocationHandler)，是调用父类Proxy的构造方法。
*父类持有：protected InvocationHandler h;
*Proxy构造方法：
* protected Proxy(InvocationHandler h) {
* Objects.requireNonNull(h);
* this.h = h;
* }
*
*/
public $Proxy0(InvocationHandler paramInvocationHandler)
throws 
{
super(paramInvocationHandler);
}
/**
* 
*这里调用代理对象的sayHello方法，直接就调用了InvocationHandler中的invoke方法，并把m3传了进去。
*this.h.invoke(this, m3, null); this.h就是父类Proxy中保存的InvocationHandler实例变量
*来，再想想，代理对象持有一个InvocationHandler对象，InvocationHandler对象持有一个被代理的对象，
*再联系到InvacationHandler中的invoke方法。嗯，就是这样。
*/
public final void sayHello()
throws 
{
try
{
this.h.invoke(this, m3, null);
return;
}
catch (RuntimeException localRuntimeException)
{
throw localRuntimeException;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
// 此处由于版面原因，省略equals()、hashCode()、toString()三个方法的代码
// 这3个方法的内容与sayHello()非常相似。
static
{
try
{
m3 = Class.forName("org.fenixsoft.bytecode.DynamicProxyTest$IHello").getMethod("sayHello", new Class[0]);
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
return;
}
catch (NoSuchMethodException localNoSuchMethodException)
{
throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
}
catch (ClassNotFoundException localClassNotFoundException)
{
throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
}
}
}