JAVA提高第七篇类加载器解析

package study.javaenhance;

import java.util.ArrayList;

public class ClassLoaderTest
{
  public static void main(String[] args) throws Exception 
  {
    //获取类加载器,那么这个获取的是一个实例对象,我们知道类加载器也有很多种,那么因此也有其对应的类存在,因此可以获取到对应的字节码
    System.out.println(ClassLoaderTest.class.getClassLoader());
    //获取类加载的字节码,然后获取到类加载字节码的名字
    System.out.println(ClassLoaderTest.class.getClassLoader().getClass().getName());
    //下面我们看下获取非我们定义的类,比如System ArrayList 等常用类
    System.out.println(System.class.getClassLoader()); 
    System.out.println(ArrayList.class.getClassLoader()); 
    
    
  }

}

package study.javaenhance;

import java.util.ArrayList;

public class ClassLoaderTest
{
  public static void main(String[] args) throws Exception 
  {
    //获取类加载器,那么这个获取的是一个实例对象,我们知道类加载器也有很多种,那么因此也有其对应的类存在,因此可以获取到对应的字节码
    System.out.println(ClassLoaderTest.class.getClassLoader());
    //获取类加载的字节码,然后获取到类加载字节码的名字
    System.out.println(ClassLoaderTest.class.getClassLoader().getClass().getName());
    //下面我们看下获取非我们定义的类,比如System ArrayList 等常用类
    System.out.println(System.class.getClassLoader()); 
    System.out.println(ArrayList.class.getClassLoader()); 
    
    
    //演示java 提供的类加载器关系
    ClassLoader classloader = ClassLoaderTest.class.getClassLoader();
    while(classloader != null)
    {
      System.out.print(classloader.getClass().getName()+"-->");
      classloader = classloader.getParent();
    }
    System.out.println(classloader); 
    
  }

}

public Class<?> loadClass(String name) throws ClassNotFoundException { 
    return loadClass(name, false); 
  } 

protected Class<?> loadClass(String name, boolean resolve)throws ClassNotFoundException{ 
     //加上锁，同步处理，因为可能是多线程在加载类 
     synchronized (getClassLoadingLock(name)) { 
       //检查，是否该类已经加载过了，如果加载过了，就不加载了 
       Class c = findLoadedClass(name); 
       if (c == null) { 
         long t0 = System.nanoTime(); 
         try { 
           //如果自定义的类加载器的parent不为null,就调用parent的loadClass进行加载类 
           if (parent != null) { 
             c = parent.loadClass(name, false); 
           } else { 
             //如果自定义的类加载器的parent为null，就调用findBootstrapClass方法查找类，就是Bootstrap类加载器 
             c = findBootstrapClassOrNull(name); 
           } 
         } catch (ClassNotFoundException e) { 
           // ClassNotFoundException thrown if class not found 
           // from the non-null parent class loader 
         } 
 
         if (c == null) { 
           // If still not found, then invoke findClass in order 
           // to find the class. 
           long t1 = System.nanoTime(); 
           //如果parent加载类失败，就调用自己的findClass方法进行类加载 
           c = findClass(name); 
 
           // this is the defining class loader; record the stats 
           sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0); 
           sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1); 
           sun.misc.PerfCounter.getFindClasses().increment(); 
         } 
       } 
       if (resolve) { 
         resolveClass(c); 
       } 
       return c; 
     } 
   } 

private Class findBootstrapClassOrNull(String name) 
  { 
    if (!checkName(name)) return null; 
 
    return findBootstrapClass(name); 
  } 

package study.javaenhance;

public class ClassLoaderAttachment {
  @Override
  public String toString() {
    return "Hello ClassLoader!";
    
  }

}

package study.javaenhance;

import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;

public class MyClassLoader extends ClassLoader
{
  //需要加载类.class文件的目录 
  private String classDir; 
   
  //无参的构造方法，用于class.newInstance()构造对象使用 
  public MyClassLoader(){ 
  } 
   
  public MyClassLoader(String classDir){ 
    this.classDir = classDir; 
  }

  @Override
  protected Class<?> findClass(String name) throws ClassNotFoundException {
    System.out.println(name);
    String classPathFile = classDir + "\\" + name.substring(name.lastIndexOf(".")+1) + ".class";
    System.out.println(classPathFile);
    try 
    {
      System.out.println("my");
       //将class文件进行解密 
      FileInputStream fis = new FileInputStream(classPathFile); 
      ByteArrayOutputStream bos = new ByteArrayOutputStream(); 
      encodeAndDecode(fis,bos); 
      byte[] classByte = bos.toByteArray(); 
      //将字节流变成一个class 
      return defineClass(classByte,0,classByte.length); 
    } catch (Exception e) 
    {
      e.printStackTrace();
    }
    
    return super.findClass(name);
  } 
  
   //测试，先将ClassLoaderAttachment.class文件加密写到工程的class_temp目录下 
  public static void main(String[] args) throws Exception{ 
    //配置运行参数 
    
    String srcPath = args[0];//ClassLoaderAttachment.class原路径 
    String desPath = args[1];//ClassLoaderAttachment.class输出的路径 
    String desFileName = srcPath.substring(srcPath.lastIndexOf("\\")+1); 
    String desPathFile = desPath + "/" + desFileName; 
    FileInputStream fis = new FileInputStream(srcPath); 
    FileOutputStream fos = new FileOutputStream(desPathFile); 
    //将class进行加密 
    encodeAndDecode(fis,fos); 
    fis.close(); 
    fos.close(); 
  } 
  
  

   /** 
   * 加密和解密算法 
   * @param is 
   * @param os 
   * @throws Exception 
   */ 
  private static void encodeAndDecode(InputStream is,OutputStream os) throws Exception{ 
    int bytes = -1; 
    while((bytes = is.read())!= -1){ 
      bytes = bytes ^ 0xff;//和0xff进行异或处理 
      os.write(bytes); 
    } 
  } 
}

package study.javaenhance;

import java.util.ArrayList;

public class ClassLoaderTest
{
  public static void main(String[] args) throws Exception 
  {
    //获取类加载器,那么这个获取的是一个实例对象,我们知道类加载器也有很多种,那么因此也有其对应的类存在,因此可以获取到对应的字节码
    System.out.println(ClassLoaderTest.class.getClassLoader());
    //获取类加载的字节码,然后获取到类加载字节码的名字
    System.out.println(ClassLoaderTest.class.getClassLoader().getClass().getName());
    //下面我们看下获取非我们定义的类,比如System ArrayList 等常用类
    System.out.println(System.class.getClassLoader()); 
    System.out.println(ArrayList.class.getClassLoader()); 
    
    
    //演示java 提供的类加载器关系
    ClassLoader classloader = ClassLoaderTest.class.getClassLoader();
    while(classloader != null)
    {
      System.out.print(classloader.getClass().getName()+"-->");
      classloader = classloader.getParent();
    }
    System.out.println(classloader); 
    
    
    
    try { 
      //Class classDate = new MyClassLoader("class_temp").loadClass("ClassLoaderAttachment"); 
      Class classDate = new MyClassLoader("class_temp").loadClass("study.javaenhance.ClassLoaderAttachment"); 
      Object object = classDate.newInstance(); 
      //输出ClassLoaderAttachment类的加载器名称 
      System.out.println("ClassLoader:"+object.getClass().getClassLoader().getClass().getName()); 
      System.out.println(object); 
    } catch (Exception e1) { 
      e1.printStackTrace(); 
    }
  }

}