jvm（四）自定义类加载器

来源：互联网发布：告白气球知乎编辑：程序博客网时间：2024/06/17 11:29

通过继承ClassLoader类覆盖findClass方法来自定义类加载器：

import java.io.ByteArrayOutputStream;import java.io.FileInputStream;import java.io.InputStream;public class MyClassLoader extends ClassLoader{public static void main(String[] args) throws Exception {MyClassLoader loader1 = new MyClassLoader();loader1.setClassPath("D:\\codePath\\classloader\\a\\");MyClassLoader loader2 = new MyClassLoader(loader1);loader2.setClassPath("D:\\codePath\\classloader\\b\\");Class<?> clazz = loader2.loadClass("LoadClass");clazz.newInstance();}public MyClassLoader(){super();}public MyClassLoader(ClassLoader loader){super(loader);}protected Class<?> findClass(String fullclassName) throws ClassNotFoundException {String classPath = this.classPath+fullclassName.replaceAll("\\.", "\\")+".class";//System.out.println(classPath);byte[] data = getClassData(classPath);if(data==null){return null;}return this.defineClass(fullclassName, data, 0, data.length);}private byte[] getClassData(String path){byte[] data = null;InputStream in = null;ByteArrayOutputStream arrayOut = null;try {in = new FileInputStream(path);arrayOut = new ByteArrayOutputStream();int ch = 0;while(-1!=(ch=in.read())){arrayOut.write(ch);}data = arrayOut.toByteArray();} catch (Exception e) {return null;} finally{try {if(in!=null)in.close();if(arrayOut!=null)arrayOut.close();} catch (Exception ex) {return null;}}return data;}private String classPath;public String getClassPath() {return classPath;}public void setClassPath(String classPath) {this.classPath = classPath;}}

加载的类：

public class LoadClass {public static int v1 = 0;public LoadClass(){System.out.println("loader is : "+this.getClass().getClassLoader());}}

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