一、概述
1.目标：动态代理的代理逻辑可以任意修改
2.思路：
(1)要把代理逻辑抽离，站在jvm的角度思考，应独立出InvocationHandler接口，并接收被代理的对象及方法作为参数invoke(Object o, Method m)，并本身作为参数传给newProxyInstance(Class interfze,InvocationHandler handler)
(2)InvocationHandler本身聚合被代理类target，以便在target的方法前后增加代理逻辑
3.知识点：
(1)按名字找方法java.lang.reflect.Method md = proxy.Movable.class.getMethod("stop");
(2)按"."拆分字符串：String [] parts = m.toString().replace("abstract ", "").split("\\.");
二、代码
1.InvocationHandler.java
2.TimeHandler.java
3.Movable.java
4.Tank.java
5.Proxy.java
6.Client.java
1.InvocationHandler.java
package proxy;
import java.lang.reflect.Method;
public interface InvocationHandler {
public void invoke(Object o, Method m);
}
2.TimeHandler.java
package proxy; import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method; public class TimeHandler implements InvocationHandler { //保留被代理的对象
private Object target; public TimeHandler(Object target) {
this.target = target;
} @Override
public void invoke(Object o, Method m) {
System.out.println("Time Proxy start...........");
long start = System.currentTimeMillis();
try {
//除了静态方法，方法的调用都要先已知对象，所以要把对象o作为参数传进去
m.invoke(target);
} catch (Exception e) {
e.printStackTrace();
}
long end = System.currentTimeMillis();
System.out.println("花费时间："+(end - start));
System.out.println("Time Proxy end..........."); } }
3.Movable.java
package proxy;
public interface Movable {
public void move();
public void stop();
}
4.Tank.java
package proxy;
import java.util.Random;
public class Tank implements Movable {
@Override
public void move() {
System.out.println("Tank moving.......");
try {
Thread.sleep(new Random().nextInt(2000));
} catch (InterruptedException e) {
e.printStackTrace();
}
}
@Override
public void stop() {
System.out.println("Tank stopping.......");
}
}
5.Proxy.java
package proxy; import java.io.File;
import java.io.FileWriter;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader; import javax.tools.JavaCompiler;
import javax.tools.JavaCompiler.CompilationTask;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider; public class Proxy { public static Object newProxyInstance(Class interfze,InvocationHandler handler) throws Exception { String rt = "\n\r"; //拼接"实现接口方法"的字符串
String methodStr = "";
for(Method m: interfze.getMethods() ){ //取出方法的修饰符和返回值类型
String [] parts = m.toString().replace("abstract ", "").split("\\.");
String [] parts2 = parts[0].split(" "); methodStr +=
"@Override" + rt +
parts2[0]+" "+parts2[1]+" "+m.getName()+"() {" + rt +
"try{"+ rt +
"java.lang.reflect.Method md = " + interfze.getName() + ".class.getMethod(\""+m.getName()+"\");" + rt +
//传this进去其实没什么用，invoke实际是调用target的方法m.invoke(target)
"handler.invoke(this, md);" + rt +
"}catch(Exception e){"+ rt +
" e.printStackTrace();" + rt +
"}" + rt + "}"+ rt ;
} //动态代理文件的源码
String str =
"package proxy;" + rt + "public class TankTimeProxy implements " + interfze.getName() + " {"+rt+ //聚合Handler
"private InvocationHandler handler;" + rt + "public TankTimeProxy(InvocationHandler handler) {" + rt +
"this.handler = handler;" + rt +
"}" + rt + methodStr + rt + "}" ; //把源码写到java文件里
File file = new File(System.getProperty("user.dir")+"/src/proxy/TankTimeProxy.java");
FileWriter fw = new FileWriter(file);
fw.write(str);
fw.flush();
fw.close(); //编译源码，生成class,注意编译环境要换成jdk才有compiler,单纯的jre没有compiler，会空指针错误
JavaCompiler jc = ToolProvider.getSystemJavaCompiler(); //文件管事器
StandardJavaFileManager fileMgr = jc.getStandardFileManager(null, null, null); //编译单元
Iterable units = fileMgr.getJavaFileObjects(file); //编译任务
CompilationTask t = jc.getTask(null, fileMgr, null, null, null, units); //编译
t.call();
fileMgr.close(); //把类load到内存里
URL[] urls = new URL[] {new URL("file:/"+System.getProperty("user.dir")+"/src/proxy/TankTimeProxy.class")};
URLClassLoader uc = new URLClassLoader(urls);
Class c = uc.loadClass("proxy.TankTimeProxy"); //生成实例
//return c.newInstance(); //c.newInstance()会调用无参数的Construtor，若类没有无参的Constructor时会出错
//Constructor ctr = c.getConstructor(interfze);
Constructor ctr = c.getConstructor(InvocationHandler.class);
return ctr.newInstance(handler);
}
}
6.Client.java
package proxy;
import java.io.IOException;
import org.junit.Test;
public class Client {
@Test
public void testProxy() throws Exception{
Movable m = (Movable)Proxy.newProxyInstance(Movable.class, new TimeHandler(new Tank()));
m.move();
m.stop();
}
}
三、运行结果