自定义ClassLoader

package com.popo.test;import java.io.File;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;public class MyClassLoader extends ClassLoader {    String filePath = "D:/myclass/";    ClassLoader parent ;    public MyClassLoader(ClassLoader parent) {        // TODO Auto-generated constructor stub        this.parent=parent;    }    @Override    protected synchronized Class<?> loadClass(String name, boolean resolve)            throws ClassNotFoundException {        // TODO Auto-generated method stub        Class c = null;        try {            c = findLoadedClass(name);            if (c != null)                return c;            try {                c = parent.loadClass(name);            } catch (ClassNotFoundException e) {                // TODO: handle exception//                e.printStackTrace();            }            if (c == null)                c = myFindClass(name);            return c;        } catch (Exception e) {            // TODO: handle exception        }        return super.loadClass(name, resolve);    }    private Class<?> myFindClass(String name) throws ClassNotFoundException {        String fname = name.replaceAll("\\.", "/");        System.out.println(name);        File classF = new File(filePath + fname + ".class");        try {            FileInputStream fin = new FileInputStream(classF);                        try {                int len = fin.available();                byte[] b = new byte[len];                fin.read(b, 0, len);                Class<?> c = defineClass(name, b, 0, len);                fin.close();                return c;            } catch (IOException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        } catch (FileNotFoundException e) {            // TODO Auto-generated catch block            e.printStackTrace();            throw (new ClassNotFoundException(name + ".class not found in " + filePath));        }        return null;    }}

测试：

先用记事本写个简单的累吧：

public class MyClass {public static void p(){System.out.println("hello in MyClass loader");}}

手动编译下 javac MyClass.java

然后把生成的class放到D:/myclass 目录下

测试类：

package com.popo.test;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;public class MyClassLaoderTest {    /**     * @param args     */    public static void main(String[] args) {        // TODO Auto-generated method stub        MyClassLaoderTest mct = new MyClassLaoderTest();        MyClassLoader m = new MyClassLoader( mct.getClass().getClassLoader());        try {            Class c = m.loadClass("MyClass",true);                        Object o =c.newInstance();                        Method method =c.getMethod("p", null);            method.invoke(o, null);        } catch (ClassNotFoundException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (InstantiationException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (IllegalAccessException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (SecurityException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (NoSuchMethodException 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();        }            }}

运行结果：

MyClass
hello in MyClass loader

yeah! Succ