package agent;
import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.Instrumentation;
import java.util.Set;
import java.util.Timer;
import java.util.TreeSet;
public  class  HotAgent {
 
    protected  static  Set<String>  clsnames=new TreeSet<String>();
 
    public  static  void  premain(String  agentArgs, Instrumentation  inst)  throws Exception {
        ClassFileTransformer  transformer =new ClassTransform(inst);
        inst.addTransformer(transformer);
        System.out.println("是不是支持類的重定義："+inst.isRedefineClassesSupported());
        Timer  timer=new  Timer();
        timer.schedule(new ReloadTask(inst),2000,2000);
    }
}

package agent;
import java.lang.instrument.ClassFileTransformer;
importjava.lang.instrument.IllegalClassFormatException;
import java.lang.instrument.Instrumentation;
import java.security.ProtectionDomain;
 
public  class  ClassTransform.  implements ClassFileTransformer {
    private  Instrumentation  inst;
 
    protected  ClassTransform(Instrumentation  inst){
        this.inst=inst;
    }
 
    /**
     * 此方法在redefineClasses時或初次加載時會調(diào)用，也就是說在class被再次加載時會被調(diào)用，
     * 并且我們通過此方法可以動態(tài)修改class字節(jié)碼，實(shí)現(xiàn)類似代理之類的功能，具體方法可以使用ASM或javasist，
     * 如果對字節(jié)碼很熟習(xí)的話可以直接修改字節(jié)碼。
     */
    public  byte[]  transform(ClassLoader  loader, String  className,
           Class<?>  classBeingRedefined, ProtectionDomain  protectionDomain,
           byte[]  classfileBuffer)throws IllegalClassFormatException {
        byte[]  transformed = null;
        HotAgent.clsnames.add(className);
        return  null;
    }
}

package agent;
import java.io.InputStream;
import java.lang.instrument.ClassDefinition;
import java.lang.instrument.Instrumentation;
import java.util.TimerTask;
 
public  class  ReloadTask  extends  TimerTask {
    private  Instrumentation  inst;
 
    protected  ReloadTask(Instrumentation  inst){
        this.inst=inst;
    }
 
    @Override
    public  void  run() {
       try{
           ClassDefinition[]  cd=new ClassDefinition[1];
           Class[]  classes=inst.getAllLoadedClasses();
           for(Class  cls:classes){
                if(cls.getClassLoader()==null||!cls.getClassLoader().getClass().getName().equals("sun.misc.Launcher$AppClassLoader"))
                    continue;
                String  name=cls.getName().replaceAll("\\.","/");
                cd[0]=new ClassDefinition(cls,loadClassBytes(cls,name+".class"));
                inst.redefineClasses(cd);
           }
       }catch(Exception ex){
            ex.printStackTrace();
       }
    }
 
    private  byte[]  loadClassBytes(Class  cls,String  clsname) throws  Exception{
        System.out.println(clsname+":"+cls);
        InputStream  is=cls.getClassLoader().getSystemClassLoader().getResourceAsStream(clsname);
        if(is==null)return  null;
        byte[]  bt=new  byte[is.available()];
        is.read(bt);
        is.close();
        return  bt;
    }
}

package test.redefine;
 
public  class  Bean1 {
    public  void  test1(){
      System.out.println("============================");
    }
}

package test.redefine;
 
public  class  Test {
    public  static  void  main(String[] args)throws  InterruptedException {
 
       Bean1  c1=new  Bean1();
       while(true){
           c1.test1();
           Thread.sleep(5000);
       }
    }
}

<Host appBase="webapps" autoDeploy="true" name="localhost" unpackWARs="true" xmlNamespaceAware="false" xmlValidation="false">  
    <Context docBase="CPCWeb" path="/CPCWeb" reloadable="true" source="org.<span class="wp_keywordlink"><a href="http://res.importnew.com/eclipse" title="Eclipse ImportNew主頁" target="_blank">Eclipse</a></span>.jst.j2ee.server:CPCWeb"/>
</Host>