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("是否支持類的重定義："+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(shí)或者初次加載時(shí)會(huì)調(diào)用，也就是說(shuō)在class被再次加載時(shí)會(huì)被調(diào)用，
   * 并且我們通過(guò)此方法可以動(dòng)態(tài)修改class字節(jié)碼，實(shí)現(xiàn)類似代理之類的功能，具體方法可使用ASM或者javasist，
   * 如果對(duì)字節(jié)碼很熟悉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  title="Eclipse ImportNew主頁(yè)" target="_blank">Eclipse</a></span>.jst.j2ee.server:CPCWeb"/>
</Host>