自定义类加载器 ( by quqi99 )

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自定义类加载器( by quqi99 )

作者：张华发表于：2010-03-12

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Method;
import java.net.URL;
import java.util.jar.JarEntry;
import java.util.jar.JarInputStream;

/**
* 自定义类加载器
* @version 0.10 2010-3-12
* @author Zhang Hua
*/
public class LicClassLoader extends ClassLoader {
    public static boolean TRACE = true;
    private static boolean isDecrypt = true; //是否加解密
    private String cp;

    public static void main(String[] args){
        LicClassLoader mcl = new LicClassLoader("E://workspace//3.4//License//bin", LicClassLoader.class.getClassLoader());
        Thread.currentThread().setContextClassLoader(mcl);
        try {
            Class c = mcl.loadClass("my.secret.code.License");
            Object LicenseObj = c.newInstance();
            //这样调用会出错，因为License是由系统类加载器加载的，而obj是由 LicClassLoader加载的，系统类加载器看不到LicClassLoader加载的LicenseObj，只能通过反射调用
//            License te = (License)LicenseObj;
            Method checkMethod = c.getMethod("validate", new Class[]{String.class});
            Object result = checkMethod.invoke(LicenseObj, new Object[]{"a"});
            System.out.println(result);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public LicClassLoader(String cp, ClassLoader parent) {
        super(parent);
        this.cp = cp;
    }

    @SuppressWarnings("unchecked")
    public Class loadClass(String className) throws ClassNotFoundException {
        return loadClass(className, false);
    }

    @SuppressWarnings("unchecked")
    protected Class loadClass(String name, boolean resolve) throws ClassNotFoundException {

        try {
            if (TRACE)
                System.out.println ("loadClass (" + name + ", " + resolve + ")");
            if(name.endsWith("Object")){
                System.out.println("");
            }
            //调用系统方法检查此类是否已经被本classloader实例加载过
            Class foundClass = findLoadedClass(name);

            //如果不是属性本classloader加载的范畴，请求父加载器加载
            if(foundClass == null){
                Class parentsVersion = null;
                try{
                    parentsVersion = getParent().loadClass(name);
                    if(parentsVersion.getClassLoader() != getParent())
                        foundClass = parentsVersion;
                }catch (Exception ignore){}
            }

            //从自定义的classloader加载
            if(foundClass == null){
                try{
//                    foundClass= findClass(name);             //从class文件找类
                    foundClass= findClassFromJar(name,"lic.jar");   //从JAR包中找类
                }catch(Exception ignore){}
            }

            //还不行，调用系统类加载器再试一次
        // if(foundClass == null){
           //     foundClass = findSystemClass(name);
         // }

            //根据情况决定是否加载关系类
            if (resolve && foundClass!=null) {
                resolveClass(foundClass);
            }
            return foundClass;
        } catch (Exception e) {
            throw new ClassNotFoundException(e.toString());
        }
    }

    //从class中找类
    public Class findClass(String className) throws ClassNotFoundException {
        if (TRACE)
            System.out.println("findClass (" + className + ")");
        final String filePath = className.replace('.', '/') + ".class";
        final URL classURL = getResource(filePath);
        if (classURL == null) {
            throw new ClassNotFoundException(className);
        } else {
            InputStream in = null;
            try {
                in = classURL.openStream();
                final byte[] classBytes = readFully(in);
                if(isDecrypt){
                    crypt(classBytes);   //加密
                    crypt(classBytes);   //解密
                    if (TRACE)
                        System.out.println("decrypted [" + className + "]");
                }
                return defineClass(className, classBytes, 0, classBytes.length);
            } catch (IOException ioe) {
                throw new ClassNotFoundException(className);
            } finally {
                if (in != null)
                    try {
                        in.close();
                    } catch (Exception ignore) {
                    }
            }
        }
    }



    //从jar中找类
    protected Class findClassFromJar(String className, String jarName) throws ClassNotFoundException {
        String jarPath = cp + File.separator + jarName;
        if(!jarPath.toLowerCase().endsWith(".jar") && !jarPath.toLowerCase().endsWith(".zip"))
            jarPath = jarPath + ".jar";
        JarInputStream in = null;
        if (!(jarPath == null || jarPath == "")) {
            try {
                in = new JarInputStream(new FileInputStream(jarPath));
                JarEntry entry;
                while ((entry = in.getNextJarEntry()) != null) {
                    if (entry.toString().equals(className.replace('.', '/') + ".class")) {
                        if (entry.getSize() == -1) {
                            System.err.println("error ： can't read the file！");
                            return null;
                        }
                        byte[] classData = new byte[(int) entry.getSize()];
                        System.out.println("It have found the file : " + className + ". Begin to read the data and load the class。");
                        in.read(classData);
                        return defineClass(className, classData, 0, classData.length);
                    }
                }
                System.out.println("Haven't found the file " + className + " in " + jarName + ".jar.");
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        } else {
            System.out.println("Haven't found the jarFile: " + jarName + ".jar.");
            return null;
        }
        return null;
    }

    /**
    * De/encrypts binary data in a given byte array. Calling the method again
    * reverses the encryption.
    */
    private static void crypt(final byte[] data) {
        for (int i = 8; i < data.length; ++i)
            data[i] ^= 0x5A;
    }

    private static byte[] readFully(final InputStream in) throws IOException {
        final ByteArrayOutputStream buf1 = new ByteArrayOutputStream();
        final byte[] buf2 = new byte[8 * 1024];
        for (int read; (read = in.read(buf2)) > 0;) {
            buf1.write(buf2, 0, read);
        }
        return buf1.toByteArray();
    }

}