Java自定义类加载器实现热部署实例

ゝ一世哀愁。 2022-11-30 12:39 135阅读 0赞

在慕课网上看到这个课程，然后照着视频敲了一遍代码，完全没问题的代码，运行的时候，就是不出现热部署的效果，把我愁死了，后来发现，无论是在eclipse还是在idea中运行，都是需要通过Debug模式运行。

这里要实现热加载部署，重点就是需要自定义我们的类加载器，然后监听类的修改时间，如果修改时间发生改变，就将其重新加载到虚拟机中。

所有代码如下：

MyClassLoader.java

package com.xxx.classloader;
    
    import java.io.ByteArrayOutputStream;
    import java.io.File;
    import java.io.FileInputStream;
    
    public class MyClassLoader extends ClassLoader{
    	private String classpath;
    	public MyClassLoader(String classpath ) {
    		super(ClassLoader.getSystemClassLoader());
    		this.classpath = classpath;
    	}
    	
    	@Override
    	protected Class<?> findClass(String name) throws ClassNotFoundException {
    		byte[] data = this.loadClassData(name);
    		
    		return this.defineClass(name, data, 0, data.length);
    	}
    
    	private byte[] loadClassData(String name) {
    		try {
    			name = name.replace(".", "//");
    			FileInputStream is = new FileInputStream(new File(classpath+name+".class"));
    			int b = 0;
    			ByteArrayOutputStream baos = new ByteArrayOutputStream();
    			while((b=is.read())!=-1) {
    				baos.write(b);
    			}
    			is.close();
    			return baos.toByteArray();
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    		return null;
    	}
    }

BaseManager.java

package com.xxx.classloader;
    
    public interface BaseManager {
    	public void logic();
    }

MyManager.java

package com.xxx.classloader;
    
    public class MyManager implements BaseManager {
    
    	@Override
    	public void logic() {
    		System.out.println("i am testing hotreload,hello.");
    	}
    
    }

LoadInfo.java

package com.xxx.classloader;
    
    public class LoadInfo {
    	private MyClassLoader myLoader;
    	private long loadTime;
    	private BaseManager manager;
    	public LoadInfo(MyClassLoader myLoader, long loadTime) {
    		//super();
    		this.myLoader = myLoader;
    		this.loadTime = loadTime;
    	}
    	public MyClassLoader getMyLoader() {
    		return myLoader;
    	}
    	public void setMyLoader(MyClassLoader myLoader) {
    		this.myLoader = myLoader;
    	}
    	public long getLoadTime() {
    		return loadTime;
    	}
    	public void setLoadTime(long loadTime) {
    		this.loadTime = loadTime;
    	}
    	public BaseManager getManager() {
    		return manager;
    	}
    	public void setManager(BaseManager manager) {
    		this.manager = manager;
    	}
    	
    }

ManagerFactory.java

package com.xxx.classloader;
    
    import java.io.File;
    import java.lang.reflect.InvocationTargetException;
    import java.util.HashMap;
    import java.util.Map;
    
    public class ManagerFactory {
    	private static final Map<String, LoadInfo> loadTimeMap = new HashMap<String, LoadInfo>();
    	private static final String CLASS_PATH = "D:/eclipse/workspaces/classloader/bin/";
    	public static final String MY_MANAGER = "com.xxx.classloader.MyManager";
    	public static BaseManager getManager(String className) {
    		File loadFile = new File(CLASS_PATH+className.replaceAll("\\.", "/") + ".class");
    		long lastModified = loadFile.lastModified();
    		System.out.println("current class loadtime -> "+lastModified);
    		if(loadTimeMap.get(className) == null) {
    			load(className,lastModified);
    		}else if(loadTimeMap.get(className).getLoadTime() != lastModified) {
    			load(className,lastModified);
    		}
    		
    		return loadTimeMap.get(className).getManager();
    	}
    	private static void load(String className, long lastModified) {
    		// TODO Auto-generated method stub
    		MyClassLoader myClassLoader = new MyClassLoader(className);
    		Class<?> loadClass = null;
    		try {
    			loadClass = myClassLoader.loadClass(className);
    		} catch (ClassNotFoundException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		
    		BaseManager manager = newInstance(loadClass);
    		LoadInfo loadInfo = new LoadInfo(myClassLoader, lastModified);
    		loadInfo.setManager(manager);
    		loadTimeMap.put(className, loadInfo);
    	}
    	private static BaseManager newInstance(Class<?> loadClass) {
    		// TODO Auto-generated method stub
    		try {
    			System.out.println("load...");
    			return (BaseManager)loadClass.getConstructor(new Class[] {}).newInstance(new Object[] {});
    		} catch (InstantiationException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		} catch (IllegalAccessException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		} catch (IllegalArgumentException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		} catch (InvocationTargetException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		} catch (NoSuchMethodException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		} catch (SecurityException e) {
    			// TODO Auto-generated catch block
    			e.printStackTrace();
    		}
    		
    		return null;
    	}
    	
    }

MsgHandler.java

package com.xxx.classloader;
    
    public class MsgHandler implements Runnable{
    	@Override
    	public void run() {
    		while(true) {
    			BaseManager manager = ManagerFactory.getManager(ManagerFactory.MY_MANAGER);
    			manager.logic();
    			try {
    				Thread.sleep(1000);
    			} catch (InterruptedException e) {
    				e.printStackTrace();
    			}
    		}
    	}
    }

ClassLoaderTest.java

package com.xxx.classloader;
    
    public class ClassLoaderTest {
    	public static void main(String[] args) {
    		new Thread(new MsgHandler()).start();
    	}
    }

运行截图：

![20200824143549685.gif][]

这篇博客的重点不在于代码本身，因为我写这篇博客也特意在网上搜索了一下，发现[cnblog][]上已经有人把代码给贡献出来，而且还给了很详细的注解。我这里要强调的是 要实现自定义类加载器实现热部署的效果，我们需要运行在Debug模式。

[20200824143549685.gif]: /images/20221123/dcbc3d2895b645159598909dd65eff2e.png
[cnblog]: https://www.cnblogs.com/niumoo/p/11756703.html