黑马程序员_类加载器

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类加载器：

系统默认三个主要类加载器，每个类负责加载特定位置的类：BootStrap、ExtClassLoader、AppClassLoader。

package cn.hmm.classLoadTest;public class classLoadDemo {public static void main(String[] args) {testClassLoad();}private static void testClassLoad() {System.out.println(classLoadDemo.class.getClassLoader().getClass().getName());//System的加载类为空是因为他是BootStrap加载的System.out.println(System.class.getClassLoader());ClassLoader loader = classLoadDemo.class.getClassLoader();while(loader != null){System.out.println(loader.getClass().getName());loader = loader.getParent();}System.out.println(loader);}}

我们可以编写自己专属的类加载器去加载加密处理的字节码

1.写一个简单的Person类,覆盖toString方法:

package cn.hmm.classLoadTest;import java.util.Date;public class Person extends Date {public String toString(){return "hello world";}}

2.编写一个加密class字节码的类,拥有加密和解密的方法,为了方便,可以使用简单的异或

package cn.hmm.classLoadTest;import java.io.*;public class MyClassLoader {public static void main(String[] args) throws IOException {// TODO 自动生成的方法存根String srcPath = args[0];String destDir = args[1];copyClassTolib(srcPath, destDir);//System.out.println(new Person());}public static void copyClassTolib(String srcPath, String destDir)throws FileNotFoundException, IOException {FileInputStream fis = new FileInputStream(srcPath);//源目标String FileName = srcPath.substring(srcPath.lastIndexOf('\\')+1);//目的地目标String destPath = destDir + "\\" + FileName;FileOutputStream fos = new FileOutputStream(destPath);//加密拷贝cypher(fis,fos);fis.close();fos.close();}public static void cypher(InputStream ips,OutputStream ops) throws IOException{int b = -1;while((b=ips.read())!=-1){//加密算法ops.write(b^0xff);}}}

3.编写自己的类加载器,用自己的类加载器解密那份加密的字节码文件

package cn.hmm.classLoadTest;import java.io.*;import java.util.Date;public class PersonLoader extends ClassLoader {public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {// TODO 自动生成的方法存根//用自己的类加载器去加载加密后的类Class clazz = new PersonLoader("D:\\workspace\\高新技术\\lib").loadClass("Person.class");System.out.println(clazz.getClassLoader().getClass().getName());Date d1 = (Date) clazz.newInstance();System.out.println(d1.toString());//父类只能加载带包名的(默认的应该是AppClassLoader)/*System.out.println(new Person().getClass().getClassLoader().getClass().getName());Class clazz = new PersonLoader().loadClass("cn.hmm.classLoadTest.Person");Date d1 = (Date) clazz.newInstance();System.out.println(d1.toString());*///直接加载//System.out.println(new Person());}@Overrideprotected Class<?> findClass(String name) throws ClassNotFoundException{String destPath = Path+"\\"+name;try{FileInputStream ips = new FileInputStream(destPath);ByteArrayOutputStream bos = new ByteArrayOutputStream();MyClassLoader.cypher(ips, bos);byte[] buf = bos.toByteArray();return defineClass(buf,0,buf.length);//return super.findClass(name);}catch(Exception e){//throw new RuntimeException(e);}return super.findClass(name);}private String Path;PersonLoader(){}PersonLoader(String Path){this.Path = Path;}}

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