自定义加密的类加载器
1、加载器初识
JVM有有三种类加载器:
*BootStrap加载JRE\lib\rt.jar
*ExtClassLoader加载JRE/lib/ext/*.jar
*AppClassLoader加载classpath指定目录下的类
2、自定义加载器
1)被加载的类
public class ClassAttachment { public ClassAttachment() { System.out.println("Hello,World"); } }
2)加密class的加密器
import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; public class Cypher { public static void main(String[] args) throws IOException { String srcPath = "D:\\Android\\reflect\\bin\\classloader\\ClassAttachment.class"; String destPath = "cypherClass"; String fileName = srcPath.substring(srcPath.lastIndexOf('\\') + 1); String destFilePath = destPath + "\\" + fileName; FileInputStream fis = new FileInputStream(srcPath); FileOutputStream fos = new FileOutputStream(destFilePath); cypher(fis, fos); fis.close(); fos.close(); } // 进行简单加密 public static void cypher(InputStream is, OutputStream os) { int b; try { while ((b = is.read()) != -1) { os.write(b ^ 0xff); } } catch (Exception e) { e.printStackTrace(); } } }
3)自定义的加载器
import java.io.ByteArrayOutputStream; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; public class MyClassLoader extends ClassLoader { // 指定存放加密的class的目录 private String classDir; public MyClassLoader() { } public MyClassLoader(String classDir) { this.classDir = classDir; } @Override protected Class> findClass(String name) throws ClassNotFoundException { // 生成加密class文件信息 String classFileName = classDir + "\\" + name.substring(name.lastIndexOf('.') + 1) + ".class"; try { System.out.println("-----through MyClassLoader-----"); FileInputStream fis = new FileInputStream(classFileName); ByteArrayOutputStream baos = new ByteArrayOutputStream(); // 解密 Cypher.cypher(fis, baos); byte[] classByte = baos.toByteArray(); fis.close(); baos.close(); // 根据byte[]生成Class return defineClass(null, classByte, 0, classByte.length); } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } return super.findClass(name); } }
4)测试自定义的加载器
public class MyClassLoaderTest { public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException { Class clazz = new MyClassLoader("cypherClass").loadClass("classloader.ClassAttachment"); clazz.newInstance(); } }
测试方法:
新建一个cypherClass目录,通过加密器加密自动编译的ClassAttachment.class,用它覆盖掉原来的.class文件,由于,类加载的过程中,会先让上一级的加载器进行加载,如果,上一级的加载器没有找到要加载的class文件,才会让下一级的类加载器进行加载,由于AppClassLoader现在可以找到加密后的ClassAttachment.class文件,所以,会出现如下错误:
[color=red]
java.lang.ClassFormatError: Incompatible magic value 889275713 in class file classloader/ClassAttachment[/color]
如果将原目录下的ClassAttachment.class文件删除掉,即让AppClassLoader找不到ClassAttachment.class文件,让下一级的类加载器进行加载,即自定义的加载器加载,程序运行成功:
运行结果:
-----through MyClassLoader-----
Hello,World