用来对原方法进行增强,类结构如下:
例子
InvocationHandler 实现类
public class MathHandler implements InvocationHandler {
private MathService service;
public MathHandler(MathService service) {
this.service = service;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
return method.invoke(service, args);
}
}
target接口
public interface MathService {
int add(int num1, int num2);
int multiply(int num1, int num2);
}
target实现
public class MathServiceImpl implements MathService {
@Override
public int add(int num1, int num2) {
return num1 + num2;
}
@Override
public int multiply(int num1, int num2) {
return num1 * num2;
}
}
生成代理
// 生成代理类的class文件
System.setProperty("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
final MathService service = (MathService)Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(),
new Class[]{MathService.class},
new MathHandler(new MathServiceImpl()));
读者可以根据堆栈图自己debug下生成的逻辑
代码执行完后,则会在classpath的com/sun/proxy下看到代理文件了,如果在ideal中,刷新下就可以看到
生成的代理类如下:
package com.sun.proxy;
import hadoop.proxy.MathService;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
/* renamed from: com.sun.proxy.$Proxy0 reason: invalid class name */
public final class C$Proxy0 extends Proxy implements MathService {
private static Method m0;
private static Method m1;
private static Method m2;
private static Method m3;
private static Method m4;
static {
try {
m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
m3 = Class.forName("hadoop.proxy.MathService").getMethod("multiply", Integer.TYPE, Integer.TYPE);
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
m4 = Class.forName("hadoop.proxy.MathService").getMethod("add", Integer.TYPE, Integer.TYPE);
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
} catch (NoSuchMethodException e) {
throw new NoSuchMethodError(e.getMessage());
} catch (ClassNotFoundException e2) {
throw new NoClassDefFoundError(e2.getMessage());
}
}
public C$Proxy0(InvocationHandler invocationHandler) {
super(invocationHandler);
}
public final int add(int i, int i2) {
try {
return ((Integer) ((Proxy) this).h.invoke(this, m4, new Object[]{Integer.valueOf(i), Integer.valueOf(i2)})).intValue();
} catch (Error | RuntimeException e) {
throw e;
} catch (Throwable th) {
throw new UndeclaredThrowableException(th);
}
}
public final boolean equals(Object obj) {
try {
return ((Boolean) ((Proxy) this).h.invoke(this, m1, new Object[]{obj})).booleanValue();
} catch (Error | RuntimeException e) {
throw e;
} catch (Throwable th) {
throw new UndeclaredThrowableException(th);
}
}
public final int hashCode() {
try {
return ((Integer) ((Proxy) this).h.invoke(this, m0, null)).intValue();
} catch (Error | RuntimeException e) {
throw e;
} catch (Throwable th) {
throw new UndeclaredThrowableException(th);
}
}
public final int multiply(int i, int i2) {
try {
return ((Integer) ((Proxy) this).h.invoke(this, m3, new Object[]{Integer.valueOf(i), Integer.valueOf(i2)})).intValue();
} catch (Error | RuntimeException e) {
throw e;
} catch (Throwable th) {
throw new UndeclaredThrowableException(th);
}
}
public final String toString() {
try {
return (String) ((Proxy) this).h.invoke(this, m2, null);
} catch (Error | RuntimeException e) {
throw e;
} catch (Throwable th) {
throw new UndeclaredThrowableException(th);
}
}
}
特点:
- 获取所有超类的方法对象
- 在实现接口的方法时,会调用InvocationHandler的invoke方法,proxy就是this,method就是反射构造的同方法签名的Method对象,args就是用户调用传入的参数
- 通常来说,用户只需要在实现的InvocationHandler的invoke方法中,加一句代码
method.invoke(具体目标类,入参)
即可完成整个代理 - flink的做法是将Method对象及入参打包成一个消息,进行发送,然后调用具体的干活组件去执行