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();
}

}