[转]Java 反射在实际开发中的应用

//candy.java
public class Candy {
    static {
        System.out.println("loading Candy");
    }
}
//cookie.java
public class Cookie {
    static {
        System.out.println("loading Cookie");
    }
}
//Gum.java
public class Gum {
    static {
        System.out.println("loading Gum");
    }
}
//TestMain.java
public class TestMain {
    public static void main(String[] args) {
        System.out.println("inside main");
        new Candy();
        System.out.println("After create Candy");
        try {
            Class.forName("com.RuntimeTypeInformation.Gum");
        } catch (ClassNotFoundException e) {
            System.out.println("Could not find Class");
        }
        System.out.println("After Class.forName");
        new Cookie();
        System.out.println("After new Cookie()");
        
    }
    static void printClassInfo(Class c){
        System.out.println("Class Name :"+c.getName()
                    +"is interface? :" + c.isInterface()
                    +"simple Name "+ c.getSimpleName()
                    );       
        
    }

package com.RuntimeTypeInformation.circle;

import java.util.Arrays;
import java.util.List;

abstract class Shape {
    void draw(){
        System.out.println(this+".draw()");
    }
    abstract public String toString();
}
class Circle extends Shape{
    @Override
    public String toString() {        return "Circle";    }
    
}
class Triangle extends Shape{
    @Override
    public String toString() {        return "Triangle";    }
    
}
public class Shapes{
    public static void main(String[] args) {
        //题外话，Arrays.asList 可变参数列表，可以把传入的多个对象转为一个list
        List<Shape> shapes = Arrays.asList(new Triangle(),new Circle());
        for (Shape shape : shapes) {
            shape.draw();
        }
    }
}

Shape shape  = new Circle();
shape.getClass()

public static void main(String[] args) {
        Class<Integer> intclass = int.class;
        intclass = Integer.class;
    }

public class Shapes{
    public static void main(String[] args) throws InstantiationException, IllegalAccessException {
        Class<Circle> circles = Circle.class;
        Circle circle = circles.newInstance();//第一：泛化class.newInstance可以直接得到具体的对象
        Class<? super Circle> shape = circles.getSuperclass();
        Object shape1 = shape.newInstance();//第二：它的父类，只能用逆变的泛型class接收，newInstance得到的是Object类型
     }
}

public interface Subject   
{   
  public void doSomething();   
}   
public class RealSubject implements Subject   
{   
  public void doSomething()   
  {   
    System.out.println( "call doSomething()" );   
  }   
}   
public class ProxyHandler implements InvocationHandler   
{   
  private Object proxied;   
     
  public ProxyHandler( Object proxied )   
  {   
    this.proxied = proxied;   
  }   
     
  public Object invoke( Object proxy, Method method, Object[] args ) throws Throwable   
  {   
    //在转调具体目标对象之前，可以执行一些功能处理

    //转调具体目标对象的方法
    return method.invoke( proxied, args);  
    
    //在转调具体目标对象之后，可以执行一些功能处理
  }    
}

public class SayHello {  
 public void say(){  
  System.out.println("hello everyone");  
 }  
}  

public class CglibProxy implements MethodInterceptor{  
 private Enhancer enhancer = new Enhancer();  
 public Object getProxy(Class clazz){  
  //设置需要创建子类的类  
  enhancer.setSuperclass(clazz);  
  enhancer.setCallback(this);  
  //通过字节码技术动态创建子类实例  
  return enhancer.create();  
 }  
 //实现MethodInterceptor接口方法  
 public Object intercept(Object obj, Method method, Object[] args,  
   MethodProxy proxy) throws Throwable {  
  System.out.println("前置代理");  
  //通过代理类调用父类中的方法  
  Object result = proxy.invokeSuper(obj, args);  
  System.out.println("后置代理");  
  return result;  
 }  
}  

public class DoCGLib {  
 public static void main(String[] args) {  
  CglibProxy proxy = new CglibProxy();  
  //通过生成子类的方式创建代理类  
  SayHello proxyImp = (SayHello)proxy.getProxy(SayHello.class);  
  proxyImp.say();  
 }  
}  

doPost(..){
//这是项目中的setvlet统一的拦截层，接下来我们看一下 actionInvoker.invoke
  ...
  else if (requestType.equalsIgnoreCase("image")) {
                try {
                    ActionClassInfo actionClassInfo = actionInvoker.getClassInfo(action, request, response);
                    actionClassInfo.setArgs(queryStringMap);
                    Object object = actionInvoker.invoke(actionClassInfo);
                    response.addHeader("accept-ranges", "bytes");
                    byte[] bytes = (byte[]) object;
                    response.addHeader("Content-type", "application/png");
                    response.addHeader("content-length", String.valueOf(bytes.length));
                    response.getOutputStream().write(bytes, 0, bytes.length);
                } catch (Exception e) {
                    e.printStackTrace();
                } catch (Throwable e) {
                    e.printStackTrace();
                } finally {
                    response.getOutputStream().flush();
                    response.getOutputStream().close();
                }
            }    
}

public Object invoke(ActionClassInfo action) throws Exception {
        // 执行方法之前
        Object cache = null;
        for (Object object : action.getProxys()) {
            if (object instanceof Intercepter){
                cache = ((Intercepter) object).before(action);
                if(cache != null && object instanceof RedisCacheHandler){
                    return cache;    //缓存的结果直接返回
                }
            }
        }
        Method method = action.getMethod();
        Object business = action.getClazz();
        Map<Object, Object> args = action.getArgs();
        method.setAccessible(true);
        Object result = method.invoke(business, args);

        // 执行方法后
        for (Object object : action.getProxys()) {
            if (object instanceof Intercepter)
                result = ((Intercepter) object).after(result, action);
        }

        return result;
    }