自定义类的加载器

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自定义类加载器类

package com.dasenlin.clazz;import java.io.ByteArrayOutputStream;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;import java.io.InputStream;/** * 自定义文件的类加载器 * @author Administrator * */public class FileSystemClassLoader extends ClassLoader {    private String rootDir;    public FileSystemClassLoader(String rootDir){        this.rootDir=rootDir;    }    @Override    protected Class<?> findClass(String name) throws ClassNotFoundException {        Class<?> c = findLoadedClass(name);        if(c!=null){            return c;        }else{            ClassLoader parent=this.getParent();            try {                c=parent.loadClass(name);            } catch (Exception e) {                //e.printStackTrace();            }    //双亲委托机制，委派给父类加载。            if(c!=null){                return c;            }else{                byte[]classData = getClassData(name);                if(classData==null){                    throw new ClassNotFoundException();                }else{                     c=defineClass(name,classData,0,classData.length);                }            }        }        return c;    }    private byte[] getClassData(String name) {        String path=rootDir+"/"+name.replace('.', '/')+".class";        InputStream is =null;        ByteArrayOutputStream baos = new ByteArrayOutputStream();        try {             is=new FileInputStream(path);             byte[]buffer =new byte[1024];             int temp=0;             while((temp=is.read(buffer))!=-1){                 baos.write(buffer, 0, temp);             }            return baos.toByteArray();        } catch (FileNotFoundException e) {            e.printStackTrace();            return null;        } catch (IOException e) {            e.printStackTrace();        }finally{            if(is!=null){                try {                    is.close();                } catch (IOException e) {                    e.printStackTrace();                }            }        }        return null;    }}

测试类

package com.dasenlin.clazz;public class TestClassLoader {    /**     * @param args     */    /**     * @param args     */    public static void main(String[] args) {        FileSystemClassLoader loader = new FileSystemClassLoader("E:/LearnJavaProjectText/myjava");        FileSystemClassLoader loader2 = new FileSystemClassLoader("E:/LearnJavaProjectText/myjava");        try {            Class<?> c = loader.loadClass("HelloWorld");            Class<?> c2 = loader2.loadClass("HelloWorld");            Class<?> c3 = loader2.loadClass("java.lang.String");            Class<?> c4 = loader2.loadClass("com.dasenlin.bean.Employ");            System.out.println(c.hashCode());            System.out.println(c2.hashCode());//不同的类加载器加载同一个class文件，他加载过来不是同一个对象；            System.out.println(c3.hashCode());//同一个类加载器加载不同的class文件，他加载过来的也不是同一个对象；            System.out.println(c2.getClassLoader());//自定义的类加载器 com.dasenlin.clazz.FileSystemClassLoader@126be4cc            System.out.println(c3.getClassLoader());//引导类加载器 null            System.out.println(c4.getClassLoader());//系统默认类加载器  sun.misc.Launcher$AppClassLoader@270ad7c0            System.out.println(c);        } catch (ClassNotFoundException e) {            e.printStackTrace();        }    }}

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