classloader 热部署

关键字: classloader 热部署
这两天一直在学习一些classloader的相关知识，看了一些文章，了解到classloader的作用之一就是实现热部署功能。于是就看了一个网络上的一个例子，然后自己实现了一个应用。虽然作出来了，但是说实话：不满意。因为在这个例子当中，只要热部署一次，就要重新new一个classloader，这样会引发什么问题我也不清楚，并且，classloader究竟实现了什么，以及一些底层的东西我还不是很了解，还要继续研究，目前的版本就是一个中间版本。以后还要优化，或者在我读完tomcat的classloader之后我在去仿照着写一个。

好了，下面介绍这个工程的构思、以及实现方式，设计思想:首先来说：这个工程至少需要是需要2个线程，一个是类似tomcat的服务线程，另外一个就是检测线程，检测变化，重新加载Class对象。我猜tomcat是采取了检测类，检测加载了的类文件变化。我没有那么实现，因为这种实现方式相对复杂，并且我的想集中解决热部署问题，而不是如何实现监控文件，所以我就采取了相对简单的方式：socket通知方式。也就是，在我重新编译一个class之后，利用socket通知检测线程，监测监测在监测到socket命令之后会自动的加载。

Java代码 
package com.cxz.classloader;   
  
import com.cxz.jiangyou.Say;   
  
import java.io.ByteArrayOutputStream;   
import java.io.File;   
import java.io.FileInputStream;   
import java.io.IOException;   
  
/**  
 * This classloader is like a template  
 * which includes pre-loadClass and after-loadClass  
 * @author Bernard  
 *  
 */  
public class ComplexClassLoader extends ClassLoader {   
  
    public ComplexClassLoader() {   
    }   
  
    public ComplexClassLoader(String defaultTargetDir) {   
        this.defaultTargetDir = defaultTargetDir;   
    }   
  
    private String defaultTargetDir = "D:\\hotdeploys\\";   
  
    public Class<?> findClass(String className) throws ClassNotFoundException {   
        byte[] classBytes = null;   
        try {   
            classBytes = loadByteCode(className);   
        } catch (IOException e) {   
            // TODO Auto-generated catch block   
            e.printStackTrace();   
        }   
        return super.defineClass(className, classBytes, 0, classBytes.length);   
    }   
  
    private byte[] loadByteCode(String className) throws IOException {   
        int ch = 0;   
        className = className.replaceAll("\\.", "\\\\") + ".class";   
        //The two slashes represent for meaning changing   
        File file = new File(defaultTargetDir + className);   
        FileInputStream in = null;   
        in = new FileInputStream(file);   
        ByteArrayOutputStream buffer = new ByteArrayOutputStream();   
        while ((ch = in.read()) != -1) {   
            buffer.write(ch);   
        }   
        in.close();   
        return buffer.toByteArray();   
    }   
  
    public String getDefaultTargetDir() {   
        return defaultTargetDir;   
    }   
  
    public void setDefaultTargetDir(String defaultTargetDir) {   
        this.defaultTargetDir = defaultTargetDir;   
    }      
}  

package com.cxz.classloader;

import com.cxz.jiangyou.Say;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;

/**
 * This classloader is like a template
 * which includes pre-loadClass and after-loadClass
 * @author Bernard
 *
 */
public class ComplexClassLoader extends ClassLoader {

	public ComplexClassLoader() {
	}

	public ComplexClassLoader(String defaultTargetDir) {
		this.defaultTargetDir = defaultTargetDir;
	}

	private String defaultTargetDir = "D:\\hotdeploys\\";

	public Class<?> findClass(String className) throws ClassNotFoundException {
		byte[] classBytes = null;
		try {
			classBytes = loadByteCode(className);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return super.defineClass(className, classBytes, 0, classBytes.length);
	}

	private byte[] loadByteCode(String className) throws IOException {
		int ch = 0;
		className = className.replaceAll("\\.", "\\\\") + ".class";
		//The two slashes represent for meaning changing
		File file = new File(defaultTargetDir + className);
		FileInputStream in = null;
		in = new FileInputStream(file);
		ByteArrayOutputStream buffer = new ByteArrayOutputStream();
		while ((ch = in.read()) != -1) {
			buffer.write(ch);
		}
		in.close();
		return buffer.toByteArray();
	}

	public String getDefaultTargetDir() {
		return defaultTargetDir;
	}

	public void setDefaultTargetDir(String defaultTargetDir) {
		this.defaultTargetDir = defaultTargetDir;
	}	
}

该类会自动加载d:\hotdeploys下的类文件．

下面这个就是测试类
Java代码

package com.cxz.classloader;   
  
import java.io.IOException;   
import java.net.ServerSocket;   
import java.net.Socket;   
  
import com.cxz.jiangyou.Say;   
  
public class MultiThreadTest implements Runnable {   
  
    private static final int portNum = 9090;   
  
    private static final int sleepCycle = 3000;   
  
    private Say sayer = null;   
  
    private ComplexClassLoader loader = new ComplexClassLoader();   
  
    private String delpoyee = "com.cxz.jiangyou.Sample";   
  
    public MultiThreadTest() {   
        hotDeploy(delpoyee);   
    }   
  
    public void startService() {   
        while (true) {   
            synchronized (sayer) {   
                sayer.say();   
            }   
            try {   
                Thread.sleep(sleepCycle);   
            } catch (InterruptedException e) {   
                // TODO Auto-generated catch block   
                e.printStackTrace();   
            }   
        }   
    }   
  
    public void hotDeploy(String name) {   
        try {   
            if (sayer != null) {   
                synchronized (sayer) {   
                    loader = new ComplexClassLoader();   
                    sayer = (Say) loader.loadClass(name).newInstance();   
                }   
                System.out.println("-------------->Hot deployment finished!");   
            } else {   
                sayer = (Say) loader.loadClass(name).newInstance();   
                System.out.println("-------------->Initialization finished!");   
            }   
  
        } catch (InstantiationException e) {   
            // TODO Auto-generated catch block   
            e.printStackTrace();   
        } catch (IllegalAccessException e) {   
            // TODO Auto-generated catch block   
            e.printStackTrace();   
        } catch (ClassNotFoundException e) {   
            // TODO Auto-generated catch block   
            e.printStackTrace();   
        }   
    }   
  
    @Override  
    public void run() {   
        ServerSocket server = null;   
        Socket socket = null;   
        try {   
            server = new ServerSocket(portNum);   
            while (true) {   
                socket = server.accept();   
                socket.close();   
                hotDeploy(delpoyee);   
            }   
        } catch (IOException e) {   
            // TODO Auto-generated catch block   
            e.printStackTrace();   
        }   
    }   
  
    public static void main(String[] args) {   
        // new MultiThreadTest().startService();   
        // new MultiThreadTest().run();   
        MultiThreadTest test = new MultiThreadTest();   
        Thread thread = new Thread(test);   
        thread.start();   
        try {   
            thread.sleep(sleepCycle);   
            //Waiting for the deployment Thread deploy the say obj.   
        } catch (InterruptedException e) {   
            // TODO Auto-generated catch block   
            e.printStackTrace();   
        }   
        test.startService();   
    }   
  
}  

package com.cxz.classloader;

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

import com.cxz.jiangyou.Say;

public class MultiThreadTest implements Runnable {

	private static final int portNum = 9090;

	private static final int sleepCycle = 3000;

	private Say sayer = null;

	private ComplexClassLoader loader = new ComplexClassLoader();

	private String delpoyee = "com.cxz.jiangyou.Sample";

	public MultiThreadTest() {
		hotDeploy(delpoyee);
	}

	public void startService() {
		while (true) {
			synchronized (sayer) {
				sayer.say();
			}
			try {
				Thread.sleep(sleepCycle);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}

	public void hotDeploy(String name) {
		try {
			if (sayer != null) {
				synchronized (sayer) {
					loader = new ComplexClassLoader();
					sayer = (Say) loader.loadClass(name).newInstance();
				}
				System.out.println("-------------->Hot deployment finished!");
			} else {
				sayer = (Say) loader.loadClass(name).newInstance();
				System.out.println("-------------->Initialization finished!");
			}

		} catch (InstantiationException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IllegalAccessException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	@Override
	public void run() {
		ServerSocket server = null;
		Socket socket = null;
		try {
			server = new ServerSocket(portNum);
			while (true) {
				socket = server.accept();
				socket.close();
				hotDeploy(delpoyee);
			}
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

	public static void main(String[] args) {
		// new MultiThreadTest().startService();
		// new MultiThreadTest().run();
		MultiThreadTest test = new MultiThreadTest();
		Thread thread = new Thread(test);
		thread.start();
		try {
			thread.sleep(sleepCycle);
			//Waiting for the deployment Thread deploy the say obj.
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		test.startService();
	}

}

main线程主要是服务线程,通过调用startService()不停的通过system.out来打印。支线程负责监听端口(9090)，当有连接信号后就重新加载类。
服务接口很简单，如下

Java代码 
package com.cxz.jiangyou;   
public interface Say{   
    public void say();   
}  

package com.cxz.jiangyou;
public interface Say{
	public void say();
}

总结：所有的customerClassLoader都要加载与之相关的类(比如：父类、包含的类)。如果你需要override loadclass(string, boolean)绕过findLoadedClass()检测，只能引发java.lang.LinkageError：duplicate class definition for name: "com/cxz/jiangyou/Sample"因此，比较通用的重新加载方式应该就是new一个用户定义的classloader

评论

1 楼 changqingonly 2009-08-10  

貌似你理解错了ClassLoader的用法了，不能每次都new一个新的ClassLoader来加载你的class文件，这样必然导致你的命名空间发生变更哈。