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java设计模式—动态代理模式


 

  类定义:

  1、被代理接口和实现类:Tank类实现了Moveable接口,能够move()

  package com.zec.disignmode;

  public interface Moveable {

  public void move();

  }

  package com.zec.disignmode;

  import java.util.Random;

  public class Tank implements Moveable{

  @Override

  public void move() {

  System.out.println("Tank moving....");

  try {

  Thread.sleep(new Random().nextInt(10000));

  } catch (InterruptedException e) {

  e.printStackTrace();

  }

  }

  }

  2、代理加工接口和实现类:TimeHandler类实现了InvocationHandler接口,能够invoke(Object object,Method m)在object的m方法前后加上自己记录时间的逻辑,并不是代理类,只是提供了对被代理类的加工逻辑;

  package com.zec.disignmode;

  import java.lang.reflect.Method;

  public interface InvocationHandler {

  public void invoke(Object o,Method m);

  }

  package com.zec.disignmode;

  import java.lang.reflect.InvocationTargetException;

  import java.lang.reflect.Method;

  public class TimeHandler implements InvocationHandler{

  @Override

  public void invoke(Object object, Method m) {

  System.out.println("Time Before "+m.getName());

  try {

  m.invoke(object);

  } catch (Exception e) {

  e.printStackTrace();

  }

  System.out.println("Time After "+m.getName());

  }

  }

  3、生成动态代理类的Proxy静态类:代理产生器,根据传进来的参数Class Intface和InvocationHandler h,产生动态代理类;从而使intface中的所有方法都加上了h中invoke方法的自定义逻辑;为了便于代理类的组合和扩展,代理类也会实现Intface接口,最终返回一个代理类对象;

  package com.zec.disignmode;

  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.StandardJavaFileManager;

  import javax.tools.ToolProvider;

  import javax.tools.JavaCompiler.CompilationTask;

  public class Proxy {

  public static Object newInstance(Class intface,InvocationHandler h) throws Exception {

  /*Generate the source code*/

  String rt = " ";

  String methodStr = "";

  for (Method method:intface.getMethods()) {

  methodStr +=

  " @Override"+rt+

  " public void "+ method.getName() +"() {"+rt+

  " try{"+rt+

  " Method m = "+ intface.getName()+".class.getMethod(""+ method.getName() +"");" + rt+

  " h.invoke(tank,m);"+rt+

  " }catch(Exception e){e.printStackTrace();}"+rt+

  " }"+rt

  ;

  }

  String src =

  "package com.zec.disignmode;"+rt+

  "import java.util.Random;"+rt+

  "import java.lang.reflect.*;"+rt+

  "public class TankTimeProxy implements "+ intface.getName() +"{"+rt+

  " "+ intface.getName() +" tank;"+rt+

  " com.zec.disignmode.InvocationHandler h;"+rt+

  " public TankTimeProxy("+ intface.getName() +" t,com.zec.disignmode.InvocationHandler h) {"+rt+

  " tank = t;"+rt+

  " this.h = h;"+rt+

  " }"+rt+

  methodStr+

  "}";

  /*Generate the java file*/

  String fileName = System.getProperty("user.dir")+"/src/com/zec/disignmode/TankTimeProxy.java";

  File f = new File(fileName);

  FileWriter fw = new FileWriter(f);

  fw.write(src);

  fw.flush();

  fw.close();

  /*Generate the class file*/

  JavaCompiler jc = ToolProvider.getSystemJavaCompiler();

  StandardJavaFileManager jfMgr = jc.getStandardFileManager(null, null, null);

  Iterable units = jfMgr.getJavaFileObjects(fileName);

  CompilationTask ct = jc.getTask(null, jfMgr, null, null, null, units);

  ct.call();

  jfMgr.close();

  /*Load the class into the memory*/

  URL[] urls = new URL[]{new URL("file:/"+System.getProperty("user.dir")+"/src")};

  URLClassLoader urlLoader = new URLClassLoader(urls);

  Class c = urlLoader.loadClass("com.zec.disignmode.TankTimeProxy");

  /*Generate the object*/

  Constructor constructor = c.getConstructor(Moveable.class,InvocationHandler.class);

  Object moveable = constructor.newInstance(new Tank(),h);

  return moveable;

  }

  }

  4、测试类

  package com.zec.disignmode;

  public class Client {

  public static void main(String[] args) {

  Moveable m = new Tank();

  LogHandler h = new LogHandler();

  try {

  Moveable moveable = (Moveable) Proxy.newInstance(Moveable.class, h);

  moveable.move();

  } catch (Exception e) {

  e.printStackTrace();

  }

  }

  }

  5、学习心得:

  (1)为了增强代理类的可扩展性,代理类和被代理类实现的是同一个接口,这样代理类可以作为被代理类再次被代理,可以实现不同功能代理的组合,本例中为Moveable;

  (2)InvocationHandler接口定义了对特定对象的方法的代理加工方法,Proxy为代理生成器,newInstance(Class intface,InvocationHandler h)方法表示对intface接口的所有方法进行加工,加工的逻辑由h的invoke方法定义;

  (3)代理生成器最后返回一个intface类型的引用,指向已经生成的动态代理类;

  (4)对于使用者来说,不必关心动态代理类的名称,只需要指定要代理的接口类型和处理类就可以了。