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一.什么是反射机制?

JAVA反射机制是指在中，对于任意一个，都能够知道这个类的所有属性和方法；对于任意一个对象，都能够调用它的任意一个方法和属性；这种动态获取的信息以及动态调用对象的方法的功能称为java语言的反射机制。

二.反射有关的API有哪些?

Class,Method,Field,Constructor,Annotation,Package,Interface等;

获取一个类的Class对象,从Class对象中可以获得类字段信息,方法,构造函数,注解,父类和接口等信息.还可以执行方法,获取属性值等.

三.如何使用反射获取类信息?

获取一个类的Class对象,从Class对象中可以get类字段信息,方法,构造函数,注解,父类和接口等信息.还可以执行方法,获取属性值等.

下面函数列出了通过Class可以获得的信息.

1: /**   2:    * getMethods(Class.class,"get"); 反射获取clss类的包含前缀pre的方法   3:    *   4:    * @param clazz   5:    * @param pre   6:    */   7:   public static void getMethods(Class
     clazz, String pre) {   8:     Method[] ms = clazz.getDeclaredMethods();   9:     for (Method m : ms) {  10:       if (m.getName().contains(pre)) {  11:         System.out.println(m);  12:       }  13:     }  14:   }

四.如何动态实例化对象?

有两种方式:

1.通过Class的newInstance()方法实例化,类必须包含参构造方法.

2.通过Class选择一个Constructor,执行Constructor的newInstance()实例化;

 

1: /**   2:    * 使用构造函数需要预先知道有哪些构造函数   1: /**   3:    * @throws Exception   4:    */   5:   public static void createObject2() throws Exception {   6:     Class
      clazz=Class.forName("java.io.BufferedInputStream");   7:     Constructor ctor=clazz.getConstructor(InputStream.class);   8:     InputStream in=InstanceObjectDemo.class.getClassLoader().getResourceAsStream("InstanceObjectDemo.java");   9:     BufferedInputStream obj=(BufferedInputStream) ctor.newInstance(in);  10:     System.out.println(obj);  11:     obj.close();  12:   }  13:   /**  14:    * 动态实例化对象  15:    * @param clazz  16:    */  17:   public static Object createObject(String className){  18:     Object obj=null;  19:     try {  20:       obj=Class.forName(className).newInstance();  21:     } catch (Exception e) {  22:       e.printStackTrace();  23:     }  24:     return obj;  25:   }

五.动态方法调用

使用Method的invoke()方法执行public的方法,对于私有方法,要先调用setAccessible(true)取消访问权限检查.

1: /**   2:    * 执行方法invoke()   3:    * @throws Exception   4:    */   5:   public static void excMethon() throws Exception{   6:       7:     String str="12abcde";   8:     Class clazz=str.getClass();   9:     Method m=clazz.getMethod("substring", int.class);  10:     String result=(String) m.invoke(str, 2);  11:     System.out.println(result);  12:   }

六.如何访问成员变量值?

1: /**   2:    * 直接获取字段值,需要取消访问权限[setAccessible(true)]   3:    * 类Point2中有x,y两个整型字段   4:    * @throws Exception   5:    */   6:   public static void accessField()throws Exception{   7:     Point2 p=new Point2(2,3);   8:     Class clazz=p.getClass();   9:     Field fx=clazz.getDeclaredField("x");  10:     Field fy=clazz.getDeclaredField("y");  11:      12:     fx.setAccessible(true);  13:     fy.setAccessible(true);  14:      15:     System.out.println(fx.get(p)+","+fy.get(p));  16:     fx.set(p, 20);  17:      18:     fy.set(p, 30);  19:     System.out.println(p);  20:      21:   }

七.数组反射工具类java.lang.reflect.Array

1: /**   2:    * 动态操作数组   3:    * @throws Exception   4:    */   5:   public static void createArray()throws Exception{   6:     Object arr=Array.newInstance(Integer.class, 10);   7:     Array.set(arr, 1, 100);   8:     Array.set(arr, 2, 200);   9:     Array.set(arr, 3, 300);  10:     System.out.println(Array.get(arr, 1));  11:     System.out.println(Array.get(arr, 2));  12:   }

八.综合示例-通过文件实例化对象

1:   2: import java.io.FileInputStream;   3: import java.lang.reflect.InvocationTargetException;   4: import java.lang.reflect.Method;   5: import java.util.ArrayList;   6: import java.util.HashMap;   7: import java.util.List;   8: import java.util.Map;   9: import java.util.Properties;  10:  11: /**  12:  * 通过属性文件实例化对象并赋值.  13:  * @author WeiCong  14:  *  15:  */  16: public class ObjectPoolFactory {  17:  18:   private Map
    
      objectPool=new HashMap
     
      ();  19:   private Properties config=new Properties();  20:    21:   public static void main(String[] args) {  22:     ObjectPoolFactory objectFactory=new ObjectPoolFactory();  23:     objectFactory.load("config.properties");  24:     try {  25:       objectFactory.initPool();  26:       objectFactory.setProperty();  27:       Student s=(Student)objectFactory.getObject("student");  28:       Person p=s.getPerson();  29:       System.out.println(p);  30:       System.out.println(s);  31:     } catch (Exception e) {  32:       e.printStackTrace();  33:     }  34:   }  35:   /**  36:    * 加载配置文件  37:    * @param filename  38:    */  39:   public void load(String filename){  40:     try(  41:       FileInputStream in=new FileInputStream(filename);  42:     ){  43:       config.load(in);  44:     }catch(Exception e){  45:       e.printStackTrace();  46:     }  47:   }  48:   /**  49:    * 根据类完整限定名创建对象  50:    * @param className  51:    * @return  52:    * @throws ClassNotFoundException  53:    * @throws InstantiationException  54:    * @throws IllegalAccessException  55:    */  56:   private  Object createObject(String className) throws ClassNotFoundException, InstantiationException, IllegalAccessException{  57:     Class clazz=Class.forName(className);  58:     return clazz.newInstance();  59:   }  60:   /**  61:    * 创建配置文件中的所有实例  62:    * @throws ClassNotFoundException  63:    * @throws InstantiationException  64:    * @throws IllegalAccessException  65:    */  66:   public void initPool() throws ClassNotFoundException, InstantiationException, IllegalAccessException{  67:     for(String name : config.stringPropertyNames()){  68:       if(!name.contains("%")){  69:         String className=config.getProperty(name);  70:         Object obj=createObject(className);  71:         objectPool.put(name, obj);  72:       }  73:     }  74:   }  75:   /**  76:    * 获取一个对象  77:    * @param classKey  78:    * @return  79:    */  80:   public Object getObject(String classKey){  81:     return objectPool.get(classKey);  82:   }  83:   /**  84:    * 为对象赋值  85:    * @throws NoSuchMethodException  86:    * @throws SecurityException  87:    * @throws IllegalAccessException  88:    * @throws IllegalArgumentException  89:    * @throws InvocationTargetException  90:    */  91:   public void setProperty() throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{  92:     for(String name : config.stringPropertyNames()){  93:       if(name.contains("%")){  94:         String[] values=config.getProperty(name).split(",");  95:         String[] tmp=name.split("%");  96:         String classKey=tmp[0];  97:         String propertyName=tmp[1];  98:         String methodName="set"+propertyName.substring(0, 1).toUpperCase()+propertyName.substring(1, propertyName.length());  99:         Object obj=getObject(classKey); 100:         // 101:         for(Method m : obj.getClass().getDeclaredMethods()){ 102:           if(methodName.equals(m.getName())){ 103:             if(m.getParameterTypes().length==values.length){ 104:               Object[] args=getParams(values,m.getParameterTypes()); 105:               m.invoke(obj,args); 106:             } 107:           } 108:         } 109:       } 110:     } 111:   } 112:   private Object[] getParams(String[] values, Class
      [] parameterTypes) { 113:     List
      
     
    

Bean

1: package zhwcong.javase.reflect;   2: /**   3:  * Bean   4:  * @author WeiCong   5:  *   6:  */   7: public class Person {   8:   private String name;   9:   private int height;  10:   private int weight;  11:   private boolean marry;  12:   private double every;  13:   public boolean isMarry() {  14:     return marry;  15:   }  16:   public void setMarry(boolean marry) {  17:     this.marry = marry;  18:   }  19:   public double getEvery() {  20:     return every;  21:   }  22:   public void setEvery(double every) {  23:     this.every = every;  24:   }  25:   public String getName() {  26:     return name;  27:   }  28:   public void setName(String name) {  29:     this.name = name;  30:   }  31:   public int getHeight() {  32:     return height;  33:   }  34:   public void setHeight(int height) {  35:     this.height = height;  36:   }  37:   public int getWeight() {  38:     return weight;  39:   }  40:   public void setWeight(int weight) {  41:     this.weight = weight;  42:   }  43:   public String toString(){  44:     return "[name='"+name+"',weight='"+weight+"',height='"+height+"',marry='"+marry+"',every='"+every+"']";  45:   }  46: }  47:

1: package zhwcong.javase.reflect;   2:   3: public class Student {   4:   private Person person;   5:     6:   private int no;   7:   8:   public Person getPerson() {   9:     return person;  10:   }  11:  12:   public void setPerson(Person person) {  13:     this.person = person;  14:   }  15:  16:   public int getNo() {  17:     return no;  18:   }  19:  20:   public void setNo(int no) {  21:     this.no = no;  22:   }  23:  24:   @Override  25:   public String toString() {  26:     return "[no='"+no+"',person='"+person+"']";  27:   }  28:    29:    30: }  31:

config.properties

1: person=zhwcong.javase.reflect.Person   2: person%weight=100   3: person%height=180   4: person%name=zhang   5: person%marry=true   6: person%every=12.33   7: student=zhwcong.javase.reflect.Student   8: student%person=person   9: student%no=11

九.一个AOP的简单示例.

1:   2:   3: import java.lang.reflect.InvocationHandler;   4: import java.lang.reflect.Method;   5: import java.lang.reflect.Proxy;   6:   7: public class MyAop {   8:   public static void main(String[] args) throws Exception {   9:     CInterface c=new C();  10:     CInterface p=(CInterface) ProxyFactory.getProxy(c);  11:     p.f1();  12:     p.f2();  13:   }  14: }  15: //5.自定义一个代理工厂  16: class ProxyFactory{  17:   public static Object getProxy(Object target)throws Exception{  18:     MyInvocationHander h=new MyInvocationHander();  19:     h.setTarget(target);  20:     return Proxy.newProxyInstance(target.getClass().getClassLoader(),target.getClass().getInterfaces(),h);  21:   }  22: }  23: //4.实现InvocationHandler的invoke方法  24: class MyInvocationHander implements InvocationHandler{  25:   private Object target;  26:   public void setTarget(Object target) {  27:     this.target = target;  28:   }  29:   @Override  30:   public Object invoke(Object proxy, Method method, Object[] args)  31:       throws Throwable {  32:     G g = new G();  33:     g.before();  34:     Object obj=method.invoke(target, args);  35:     g.after();  36:     return obj;  37:   }  38: }  39: //1.目标类接口  40: interface CInterface{  41:   public void f1();  42:   public void f2();  43: }  44: //2.目标类  45: class C implements CInterface{  46:   public void f1(){  47:     System.out.println("f1");  48:   }  49:   public void f2(){  50:     System.out.println("f2");  51:   }  52: }  53: //3.通用操作  54: class G{  55:   public void before(){  56:     System.out.println("===在方法前执行===");  57:   }  58:   public void after(){  59:     System.out.println("===在方法后执行===");  60:   }  61: }

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