java内部类的应用场景

Posted 2022-11-28 wuqiqing_1

场景一：

      jdk 中动态代理原理：

package dynamic.proxy;   
import java.lang.reflect.InvocationHandler;  
import java.lang.reflect.Method;  
import java.lang.reflect.Proxy;  
/** 
 * 实现自己的InvocationHandler 
 * @author zyb 
 * @since 2012-8-9 
 * 
 */  
public class MyInvocationHandler implements InvocationHandler        
    // 目标对象   
    private Object target;      
   /** 
     * 构造方法 
     * @param target 目标对象  
     */  
    public MyInvocationHandler(Object target)   
        super();  
        this.target = target;  
       
    /** 
     * 执行目标对象的方法 
     */  
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable           
        // 在目标对象的方法执行之前简单的打印一下  
        System.out.println("------------------before------------------");          
        // 执行目标对象的方法  
        Object result = method.invoke(target, args);           
        // 在目标对象的方法执行之后简单的打印一下  
        System.out.println("-------------------after------------------");           
        return result;  
        
    /** 
     * 获取目标对象的代理对象 
     * @return 代理对象 
     */  
    public Object getProxy()   
        return Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(),   
                target.getClass().getInterfaces(), this);  
      
  

public interface UserService    
    /** 
     * 目标方法  
     */  
    public abstract void add();  
  
  
  

public class UserServiceImpl implements UserService   
  
    /* (non-Javadoc) 
     * @see dynamic.proxy.UserService#add() 
     */  
    public void add()   
        System.out.println("--------------------add---------------");  
      
  

public class ProxyTest   
    @Test  
    public void testProxy() throws Throwable   
        // 实例化目标对象  
        UserService userService = new UserServiceImpl();          
        // 实例化InvocationHandler  
        MyInvocationHandler invocationHandler = new MyInvocationHandler(userService);          
        // 根据目标对象生成代理对象  
        UserService proxy = (UserService) invocationHandler.getProxy();          
        // 调用代理对象的方法  
        proxy.add();  
          
      
  

/** 
 * loader:类加载器 
 * interfaces:目标对象实现的接口 
 * h:InvocationHandler的实现类 
 */  
public static Object newProxyInstance(ClassLoader loader,  
                      Class<?>[] interfaces,  
                      InvocationHandler h)  
    throws IllegalArgumentException  
      
    if (h == null)   
        throw new NullPointerException();  
      
  
    /* 
     * Look up or generate the designated proxy class. 
     */  
    Class cl = getProxyClass(loader, interfaces);  
  
    /* 
     * Invoke its constructor with the designated invocation handler. 
     */  
    try   
            // 调用代理对象的构造方法（也就是$Proxy0(InvocationHandler h)）  
        Constructor cons = cl.getConstructor(constructorParams);  
            // 生成代理类的实例并把MyInvocationHandler的实例传给它的构造方法  
        return (Object) cons.newInstance(new Object[]  h );  
     catch (NoSuchMethodException e)   
        throw new InternalError(e.toString());  
     catch (IllegalAccessException e)   
        throw new InternalError(e.toString());  
     catch (InstantiationException e)   
        throw new InternalError(e.toString());  
     catch (InvocationTargetException e)   
        throw new InternalError(e.toString());  
      
      

public static Class<?> getProxyClass(ClassLoader loader,   
                                         Class<?>... interfaces)  
    throws IllegalArgumentException  
      
    // 如果目标类实现的接口数大于65535个则抛出异常（我XX，谁会写这么NB的代码啊？）  
    if (interfaces.length > 65535)   
        throw new IllegalArgumentException("interface limit exceeded");  
      
  
    // 声明代理对象所代表的Class对象（有点拗口）  
    Class proxyClass = null;  
  
    String[] interfaceNames = new String[interfaces.length];  
  
    Set interfaceSet = new HashSet();   // for detecting duplicates  
  
    // 遍历目标类所实现的接口  
    for (int i = 0; i < interfaces.length; i++)   
          
        // 拿到目标类实现的接口的名称  
        String interfaceName = interfaces[i].getName();  
        Class interfaceClass = null;  
        try   
        // 加载目标类实现的接口到内存中  
        interfaceClass = Class.forName(interfaceName, false, loader);  
         catch (ClassNotFoundException e)   
          
        if (interfaceClass != interfaces[i])   
        throw new IllegalArgumentException(  
            interfaces[i] + " is not visible from class loader");  
          
  
        // 中间省略了一些无关紧要的代码 .......  
          
        // 把目标类实现的接口代表的Class对象放到Set中  
        interfaceSet.add(interfaceClass);  
  
        interfaceNames[i] = interfaceName;  
      
  
    // 把目标类实现的接口名称作为缓存（Map）中的key  
    Object key = Arrays.asList(interfaceNames);  
  
    Map cache;  
      
    synchronized (loaderToCache)   
        // 从缓存中获取cache  
        cache = (Map) loaderToCache.get(loader);  
        if (cache == null)   
        // 如果获取不到，则新建地个HashMap实例  
        cache = new HashMap();  
        // 把HashMap实例和当前加载器放到缓存中  
        loaderToCache.put(loader, cache);  
          
  
      
  
    synchronized (cache)   
  
        do   
        // 根据接口的名称从缓存中获取对象  
        Object value = cache.get(key);  
        if (value instanceof Reference)   
            proxyClass = (Class) ((Reference) value).get();  
          
        if (proxyClass != null)   
            // 如果代理对象的Class实例已经存在，则直接返回  
            return proxyClass;  
         else if (value == pendingGenerationMarker)   
            try   
            cache.wait();  
             catch (InterruptedException e)   
              
            continue;  
         else   
            cache.put(key, pendingGenerationMarker);  
            break;  
          
         while (true);  
      
  
    try   
        // 中间省略了一些代码 .......  
          
        // 这里就是动态生成代理对象的最关键的地方  
        byte[] proxyClassFile = ProxyGenerator.generateProxyClass(  
            proxyName, interfaces);  
        try   
            // 根据代理类的字节码生成代理类的实例  
            proxyClass = defineClass0(loader, proxyName,  
            proxyClassFile, 0, proxyClassFile.length);  
         catch (ClassFormatError e)   
            throw new IllegalArgumentException(e.toString());  
          
          
        // add to set of all generated proxy classes, for isProxyClass  
        proxyClasses.put(proxyClass, null);  
  
       
    // 中间省略了一些代码 .......  
      
    return proxyClass;  
      
public static byte[] generateProxyClass(final String name,  
                                           Class[] interfaces)  
     
       ProxyGenerator gen = new ProxyGenerator(name, interfaces);  
    // 这里动态生成代理类的字节码，由于比较复杂就不进去看了  
       final byte[] classFile = gen.generateClassFile();  
  
    // 如果saveGeneratedFiles的值为true，则会把所生成的代理类的字节码保存到硬盘上  
       if (saveGeneratedFiles)   
           java.security.AccessController.doPrivileged(  
           new java.security.PrivilegedAction<Void>()   
               public Void run()   
                   try   
                       FileOutputStream file =  
                           new FileOutputStream(dotToSlash(name) + ".class");  
                       file.write(classFile);  
                       file.close();  
                       return null;  
                    catch (IOException e)   
                       throw new InternalError(  
                           "I/O exception saving generated file: " + e);  
                     
                 
           );  
         
  
    // 返回代理类的字节码  
       return classFile;  
     

那就是由谁来调用InvocationHandler的invoke方法的？？？

package dynamic.proxy;   
  
import java.io.FileOutputStream;  
import java.io.IOException;  
  
import sun.misc.ProxyGenerator;  
  
/** 
 * 代理类的生成工具 
 * @author zyb 
 * @since 2012-8-9 
 */  
public class ProxyGeneratorUtils   
  
    /** 
     * 把代理类的字节码写到硬盘上 
     * @param path 保存路径 
     */  
    public static void writeProxyClassToHardDisk(String path)   
        // 第一种方法，这种方式在刚才分析ProxyGenerator时已经知道了  
        // System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", true);  
          
        // 第二种方法  
          
        // 获取代理类的字节码  
        byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy11", UserServiceImpl.class.getInterfaces());  
          
        FileOutputStream out = null;  
          
        try   
            out = new FileOutputStream(path);  
            out.write(classFile);  
            out.flush();  
         catch (Exception e)   
            e.printStackTrace();  
         finally   
            try   
                out.close();  
             catch (IOException e)   
                e.printStackTrace();  
              
          
      
  
  
package dynamic.proxy;   
  
import org.junit.Test;  
  
/** 
 * 动态代理测试类 
 * @author zyb 
 * @since 2012-8-9 
 * 
 */  
public class ProxyTest   
  
    @Test  
    public void testProxy() throws Throwable   
        // 实例化目标对象  
        UserService userService = new UserServiceImpl();  
          
        // 实例化InvocationHandler  
        MyInvocationHandler invocationHandler = new MyInvocationHandler(userService);  
          
        // 根据目标对象生成代理对象  
        UserService proxy = (UserService) invocationHandler.getProxy();  
          
        // 调用代理对象的方法  
        proxy.add();  
          
      
      
    @Test  
    public void testGenerateProxyClass()   
        ProxyGeneratorUtils.writeProxyClassToHardDisk("F:/$Proxy11.class");  
      
  
import dynamic.proxy.UserService;  
import java.lang.reflect.*;  
  
public final class $Proxy11 extends Proxy  
    implements UserService  
  
  
    // 构造方法，参数就是刚才传过来的MyInvocationHandler类的实例  
    public $Proxy11(InvocationHandler invocationhandler)  
      
        super(invocationhandler);  
      
  
    public final boolean equals(Object obj)  
      
        try  
          
            return ((Boolean)super.h.invoke(this, m1, new Object[]   
                obj  
            )).booleanValue();  
          
        catch(Error _ex)    
        catch(Throwable throwable)  
          
            throw new UndeclaredThrowableException(throwable);  
          
      
  
    /** 
     * 这个方法是关键部分 
     */  
    public final void add()  
      
        try  
          
            // 实际上就是调用MyInvocationHandler的public Object invoke(Object proxy, Method method, Object[] args)方法，第二个问题就解决了  
            super.h.invoke(this, m3, null);  
            return;  
          
        catch(Error _ex)    
        catch(Throwable throwable)  
          
            throw new UndeclaredThrowableException(throwable);  
          
      
  
    public final int hashCode()  
      
        try  
          
            return ((Integer)super.h.invoke(this, m0, null)).intValue();  
          
        catch(Error _ex)    
        catch(Throwable throwable)  
          
            throw new UndeclaredThrowableException(throwable);  
          
      
  
    public final String toString()  
      
        try  
          
            return (String)super.h.invoke(this, m2, null);  
          
        catch(Error _ex)    
        catch(Throwable throwable)  
          
            throw new UndeclaredThrowableException(throwable);  
          
      
  
    private static Method m1;  
    private static Method m3;  
    private static Method m0;  
    private static Method m2;  
  
    // 在静态代码块中获取了4个方法：Object中的equals方法、UserService中的add方法、Object中的hashCode方法、Object中toString方法  
    static   
      
        try  
          
            m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[]   
                Class.forName("java.lang.Object")  
            );  
            m3 = Class.forName("dynamic.proxy.UserService").getMethod("add", new Class[0]);  
            m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);  
            m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);  
          
        catch(NoSuchMethodException nosuchmethodexception)  
          
            throw new NoSuchMethodError(nosuchmethodexception.getMessage());  
          
        catch(ClassNotFoundException classnotfoundexception)  
          
            throw new NoClassDefFoundError(classnotfoundexception.getMessage());  
          
      
 

2、回调函数

   

//当连接超时的情况下，做一个时间限定，让等待时间缩短
		Callable<String> call = new Callable<String>() 
            public String call() throws Exception   
                //开始执行耗时操作  
            	return getHttpServiceData(urlT + "?method=updateUser&check=" + getCheck(userHttpT), userHttpJson);
             
        ;  
		try 
            Future<String> future = exec.submit(call);