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
1 package proxy;
2
3 import java.lang.reflect.Method;
4
5 public interface InvocationHandler {
6 public void invoke(Object o, Method m);
7 }
2.TimeHandler.java
1 package proxy;
2
3 import java.lang.reflect.InvocationTargetException;
4 import java.lang.reflect.Method;
5
6 public class TimeHandler implements InvocationHandler {
7
8 //保留被代理的对象
9 private Object target;
10
11 public TimeHandler(Object target) {
12 this.target = target;
13 }
14
15 @Override
16 public void invoke(Object o, Method m) {
17 System.out.println("Time Proxy start...........");
18 long start = System.currentTimeMillis();
19 try {
20 //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
21 m.invoke(target);
22 } catch (Exception e) {
23 e.printStackTrace();
24 }
25 long end = System.currentTimeMillis();
26 System.out.println("花费时间："+(end - start));
27 System.out.println("Time Proxy end...........");
28
29 }
30
31 }
3.Movable.java
1 package proxy;
2
3 public interface Movable {
4 public void move();
5 public void stop();
6 }
4.Tank.java
1 package proxy;
2
3 import java.util.Random;
4
5 public class Tank implements Movable {
6
7 @Override
8 public void move() {
9 System.out.println("Tank moving.......");
10 try {
11 Thread.sleep(new Random().nextInt(2000));
12 } catch (InterruptedException e) {
13 e.printStackTrace();
14 }
15 }
16
17 @Override
18 public void stop() {
19 System.out.println("Tank stopping.......");
20
21 }
22
23 }
5.Proxy.java
1 package proxy;
2
3 import java.io.File;
4 import java.io.FileWriter;
5 import java.lang.reflect.Constructor;
6 import java.lang.reflect.Method;
7 import java.net.URL;
8 import java.net.URLClassLoader;
9
10 import javax.tools.JavaCompiler;
11 import javax.tools.JavaCompiler.CompilationTask;
12 import javax.tools.StandardJavaFileManager;
13 import javax.tools.ToolProvider;
14
15 public class Proxy {
16
17 public static Object newProxyInstance(Class interfze,InvocationHandler handler) throws Exception {
18
19 String rt = "\n\r";
20
21 //拼接"实现接口方法"的字符串
22 String methodStr = "";
23 for(Method m: interfze.getMethods() ){
24
25 //取出方法的修饰符和返回值类型
26 String [] parts = m.toString().replace("abstract ", "").split("\\.");
27 String [] parts2 = parts[0].split(" ");
28
29 methodStr +=
30 "@Override" + rt +
31 parts2[0]+" "+parts2[1]+" "+m.getName()+"() {" + rt +
32 "try{"+ rt +
33 "java.lang.reflect.Method md = " + interfze.getName() + ".class.getMethod(\""+m.getName()+"\");" + rt +
34 //传this进去其实没什么用，invoke实际是调用target的方法m.invoke(target)
35 "handler.invoke(this, md);" + rt +
36 "}catch(Exception e){"+ rt +
37 " e.printStackTrace();" + rt +
38 "}" + rt +
39
40
41 "}"+ rt ;
42 }
43
44
45 //动态代理文件的源码
46 String str =
47 "package proxy;" + rt +
48
49 "public class TankTimeProxy implements " + interfze.getName() + " {"+rt+
50
51
52 //聚合Handler
53 "private InvocationHandler handler;" + rt +
54
55 "public TankTimeProxy(InvocationHandler handler) {" + rt +
56 "this.handler = handler;" + rt +
57 "}" + rt +
58
59 methodStr + rt +
60
61 "}" ;
62
63 //把源码写到java文件里
64 File file = new File(System.getProperty("user.dir")+"/src/proxy/TankTimeProxy.java");
65 FileWriter fw = new FileWriter(file);
66 fw.write(str);
67 fw.flush();
68 fw.close();
69
70 //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
71 JavaCompiler jc = ToolProvider.getSystemJavaCompiler();
72
73 //文件管事器
74 StandardJavaFileManager fileMgr = jc.getStandardFileManager(null, null, null);
75
76 //编译单元
77 Iterable units = fileMgr.getJavaFileObjects(file);
78
79 //编译任务
80 CompilationTask t = jc.getTask(null, fileMgr, null, null, null, units);
81
82 //编译
83 t.call();
84 fileMgr.close();
85
86 //把类load到内存里
87 URL[] urls = new URL[] {new URL("file:/"+System.getProperty("user.dir")+"/src/proxy/TankTimeProxy.class")};
88 URLClassLoader uc = new URLClassLoader(urls);
89 Class c = uc.loadClass("proxy.TankTimeProxy");
90
91 //生成实例
92 //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
93 //Constructor ctr = c.getConstructor(interfze);
94 Constructor ctr = c.getConstructor(InvocationHandler.class);
95 return ctr.newInstance(handler);
96 }
97 }
6.Client.java
1 package proxy;
2
3 import java.io.IOException;
4
5 import org.junit.Test;
6
7 public class Client {
8
9 @Test
10 public void testProxy() throws Exception{
11
12 Movable m = (Movable)Proxy.newProxyInstance(Movable.class, new TimeHandler(new Tank()));
13 m.move();
14 m.stop();
15
16 }
17 }
三、运行结果
时间： 2024-10-29 05:22:57