快捷導(dǎo)航

Java動(dòng)態(tài)代理的應(yīng)用詳解

更新時(shí)間：2013年05月04日 14:27:32 作者：

本篇文章介紹了，Java動(dòng)態(tài)代理的應(yīng)用詳解，需要的朋友參考下

動(dòng)態(tài)代理其實(shí)就是java.lang.reflect.Proxy類動(dòng)態(tài)的根據(jù)您指定的所有接口生成一個(gè)class byte，該class會(huì)繼承Proxy類，并實(shí)現(xiàn)所有你指定的接口（您在參數(shù)中傳入的接口數(shù)組）；然后再利用您指定的classloader將 class byte加載進(jìn)系統(tǒng)，最后生成這樣一個(gè)類的對(duì)象，并初始化該對(duì)象的一些值，如invocationHandler,以即所有的接口對(duì)應(yīng)的Method成員。初始化之后將對(duì)象返回給調(diào)用的客戶端。這樣客戶端拿到的就是一個(gè)實(shí)現(xiàn)你所有的接口的Proxy對(duì)象。請(qǐng)看實(shí)例分析：

復(fù)制代碼代碼如下:

package com.fans.common.proxy;

public interface BusinessProcessor {
public void processBusiness();
}

復(fù)制代碼代碼如下:

package com.fans.common.proxy;
/**
* 業(yè)務(wù)處理類
* @author fanshadoop
*
*/
public class BusinessProcessorImpl implements BusinessProcessor {

@Override
public void processBusiness() {
System.out.println("processing business.....");

}

復(fù)制代碼代碼如下:

package com.fans.common.proxy;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
/**
* 業(yè)務(wù)代理類
* @author fanshadoop
*
*/
public class BusinessProcessorHandler implements InvocationHandler {

private Object target = null;

BusinessProcessorHandler(Object target) {
this.target = target;
}

public Object invoke(Object proxy, Method method, Object[] args)
   throws Throwable {
  System.out
    .println("You can do something here before process your business");
  Object result = method.invoke(target, args);
  System.out
    .println("You can do something here after process your business");
  return result;
}

}

復(fù)制代碼代碼如下:

package com.fans.common.proxy;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.Proxy;

public class Test {

/**
* @param args
*/
public static void main(String[] args) {
  BusinessProcessorImpl bpimpl = new BusinessProcessorImpl();
  BusinessProcessorHandler handler = new BusinessProcessorHandler(bpimpl);
  BusinessProcessor bp = (BusinessProcessor) Proxy.newProxyInstance(
    bpimpl.getClass().getClassLoader(), bpimpl.getClass()
      .getInterfaces(), handler);
  bp.processBusiness();

System.out.println(bp.getClass().getName());
printClassDefinition(bp.getClass());
}

public static String getModifier(int modifier) {
  String result = "";
  switch (modifier) {
  case Modifier.PRIVATE:
   result = "private";
  case Modifier.PUBLIC:
   result = "public";
  case Modifier.PROTECTED:
   result = "protected";
  case Modifier.ABSTRACT:
   result = "abstract";
  case Modifier.FINAL:
   result = "final";
  case Modifier.NATIVE:
   result = "native";
  case Modifier.STATIC:
   result = "static";
  case Modifier.SYNCHRONIZED:
   result = "synchronized";
  case Modifier.STRICT:
   result = "strict";
  case Modifier.TRANSIENT:
   result = "transient";
  case Modifier.VOLATILE:
   result = "volatile";
  case Modifier.INTERFACE:
   result = "interface";
  }
  return result;
}

public static void printClassDefinition(Class clz) {

  String clzModifier = getModifier(clz.getModifiers());
  if (clzModifier != null && !clzModifier.equals("")) {
   clzModifier = clzModifier + " ";
  }
  String superClz = clz.getSuperclass().getName();
  if (superClz != null && !superClz.equals("")) {
   superClz = "extends " + superClz;
  }
  Class[] interfaces = clz.getInterfaces();
  String inters = "";
  for (int i = 0; i < interfaces.length; i++) {
   if (i == 0) {
    inters += "implements ";
   }
   inters += interfaces[i].getName();
  }
  System.out.println(clzModifier + clz.getName() + " " + superClz + " "
    + inters);
  System.out.println("{");
  Field[] fields = clz.getDeclaredFields();
  for (int i = 0; i < fields.length; i++) {
   String modifier = getModifier(fields[i].getModifiers());
   if (modifier != null && !modifier.equals("")) {
    modifier = modifier + " ";
   }
   String fieldName = fields[i].getName();
   String fieldType = fields[i].getType().getName();
   System.out.println("    " + modifier + fieldType + " " + fieldName
     + ";");
  }

System.out.println();

  Method[] methods = clz.getDeclaredMethods();
  for (int i = 0; i < methods.length; i++) {
   Method method = methods[i];

   String modifier = getModifier(method.getModifiers());
   if (modifier != null && !modifier.equals("")) {
    modifier = modifier + " ";
   }
   String methodName = method.getName();
   Class returnClz = method.getReturnType();
   String retrunType = returnClz.getName();

   Class[] clzs = method.getParameterTypes();
   String paraList = "(";
   for (int j = 0; j < clzs.length; j++) {
    paraList += clzs[j].getName();
    if (j != clzs.length - 1) {
     paraList += ", ";
    }
   }
   paraList += ")";
   clzs = method.getExceptionTypes();
   String exceptions = "";
   for (int j = 0; j < clzs.length; j++) {
    if (j == 0) {
     exceptions += "throws ";
    }
    exceptions += clzs[j].getName();
    if (j != clzs.length - 1) {
     exceptions += ", ";
    }
   }
   exceptions += ";";
   String methodPrototype = modifier + retrunType + " " + methodName
     + paraList + exceptions;

   System.out.println("    " + methodPrototype);
  }
  System.out.println("}");
}
}

運(yùn)行結(jié)果：

復(fù)制代碼代碼如下:

You can do something here before process your business
processing business.....
You can do something here after process your business
$Proxy0
$Proxy0 extends java.lang.reflect.Proxy implements com.fans.common.proxy.BusinessProcessor
{
    java.lang.reflect.Method m1;
    java.lang.reflect.Method m3;
    java.lang.reflect.Method m0;
    java.lang.reflect.Method m2;

    boolean equals(java.lang.Object);
    java.lang.String toString();
    int hashCode();
    void processBusiness();
}

類BusinessProcessorHandler實(shí)現(xiàn)了InvocationHandler接口的invoke方法，這個(gè)類就是Proxy最終調(diào)用固定接口方法。

很明顯，Proxy.newProxyInstance方法會(huì)做如下幾件事：
    1，根據(jù)傳入的第二個(gè)參數(shù)interfaces動(dòng)態(tài)生成一個(gè)類，實(shí)現(xiàn)interfaces中的接口，該例中即BusinessProcessor接口的processBusiness方法。并且繼承了Proxy類，重寫了hashcode,toString,equals等三個(gè)方法。具體實(shí)現(xiàn)可參看 ProxyGenerator.generateProxyClass(...); 該例中生成了$Proxy0類
    2，通過傳入的第一個(gè)參數(shù)classloder將剛生成的類加載到j(luò)vm中。即將$Proxy0類load
    3，利用第三個(gè)參數(shù)，調(diào)用$Proxy0的$Proxy0(InvocationHandler)構(gòu)造函數(shù) 創(chuàng)建$Proxy0的對(duì)象，并且用interfaces參數(shù)遍歷其所有接口的方法，并生成Method對(duì)象初始化對(duì)象的幾個(gè)Method成員變量
    4，將$Proxy0的實(shí)例返回給客戶端。
現(xiàn)在好了。我們?cè)倏纯蛻舳嗽趺凑{(diào)就清楚了。
    1，客戶端拿到的是$Proxy0的實(shí)例對(duì)象，由于$Proxy0繼承了BusinessProcessor，因此轉(zhuǎn)化為BusinessProcessor沒任何問題。
         BusinessProcessor bp = (BusinessProcessor)Proxy.newProxyInstance(....);
    2，bp.processBusiness()；
         實(shí)際上調(diào)用的是$Proxy0.processBusiness();那么$Proxy0.processBusiness()的實(shí)現(xiàn)就是通過InvocationHandler去調(diào)用invoke方法啦!

您可能感興趣的文章: