Java的反射

Java的反射非常強大，傳遞class， 可以動態的生成該類、取得這個類的所有信息，包括裏面的屬性、方法以及構造函數等，甚至可以取得其父類或父接口裏面的內容。

  obj.getClass().getDeclaredMethods();//取得obj類中自己定義的方法， 包括私有的方法。

  obj.getClass().getMethods();//取得obj類中自己定義的方法及繼承過來的方法， 但私有方法得不到。

  同樣， 對field也是一樣，obj.getClass().getDeclaredFields();取得的是這個類中所有的屬性，包括私有的field; 對obj.getClass().getFields();//取得是自己以及接繼承來的屬性， 但不能取得自己的私有屬性。

static Object create(Class clazz) throws Exception {
    Constructor con = clazz.getConstructor(String.class);
    Object obj = con.newInstance("test name");
    return obj;
  }

  static void invoke1(Object obj, String methodName)
      throws IllegalArgumentException, IllegalAccessException,
      InvocationTargetException, Exception, NoSuchMethodException {
    Method[] ms = obj.getClass().getDeclaredMethods();
    ms = obj.getClass().getMethods();
    for (Method m : ms) {
      // System.out.println(m.getName());
      if (methodName.equals(m.getName()))
        m.invoke(obj, null);
    }

    Method m = obj.getClass().getMethod(methodName, null);
    m.invoke(obj, null);
  }

  static void field(Class clazz) throws Exception {
    Field[] fs = clazz.getDeclaredFields();
    //fs = clazz.getFields();
    for (Field f : fs)
      System.out.println(f.getName());
  }

  static void annon(Class clazz) throws Exception {
    Annotation[] as = clazz.getAnnotations();
  }
package com.yuqiaotech.simplejee.javase.reflect;

import java.beans.BeanInfo;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
/**
 * 使用BeanInfo來設置和讀取對象的屬性。
 */
public class BeanInfoSample {
    static class User{
        private String username;
        private String password;
        private String gender;
        public String getUsername() {
            return username;
        }
        public void setUsername(String username) {
            this.username = username;
        }
        public String getPassword() {
            return password;
        }
        public void setPassword(String password) {
            this.password = password;
        }
        public String getGender() {
            return gender;
        }
        public void setGender(String gender) {
            this.gender = gender;
        }
    }
    public static void main(String[] args) throws Exception {
        User u = new User();
        u.setUsername("Tom");
        u.setPassword("123");
        u.setGender("male");

        BeanInfo beanInfo = Introspector.getBeanInfo(User.class);
        PropertyDescriptor[] propertyDescriptors = beanInfo.getPropertyDescriptors();
        for (PropertyDescriptor pd : propertyDescriptors) {
            String proName = pd.getName();
            Object v = pd.getReadMethod().invoke(u, null);
            System.out.println(proName+"="+v);
        }
    }
}
package com.yuqiaotech.simplejee.javase.reflect;

import java.lang.reflect.*;
/**
 * 1、獲取類的相關信息
 * 2、知道類名，實例化出對象
 * 3、動態調用實例的方法
 *
 *
 */
public class ReflectSample {
    public static void main(String[] args) throws Exception {
        classInfo("com.yuqiaotech.simplejee.dao.BaseDao");
        newInstanceAndIncokeMethod();
    }
    private static void classInfo(String className) throws ClassNotFoundException{
        Class clazz = Class.forName(className);

        System.out.println("all implemented interfaces");
        Class[] allInterfaces = clazz.getInterfaces();
        for (int i = 0; i < allInterfaces.length; i++) {
            System.out.println(i+"."+allInterfaces[i]);
        }
        System.out.println("all super classes");
        Class superClass = clazz.getSuperclass();
        int i = 0;
        while(superClass != null){
            System.out.println(++i+"."+superClass);
            superClass = superClass.getSuperclass();
        }
        System.out.println("methods");
        Method[] methods = clazz.getMethods();
        for (int j = 0; j < methods.length; j++) {
            Method m = methods[j];
            System.out.println(j+"."+m.getName());
        }
        System.out.println("getConstructors");
        int k = 0;
        Constructor[] cs = String.class.getConstructors();
        for (Constructor c : cs) {
            System.out.println(++k+"."+c);
        }
    }
    private static void newInstanceAndIncokeMethod() throws SecurityException, NoSuchMethodException, IllegalArgumentException, InstantiationException, IllegalAccessException, InvocationTargetException, ClassNotFoundException{
        class Point{
            int x;
            int y;
            public Point(int x, int y){
                this.x = x;
                this.y = y;
            }
            public Point(){
            }
            public int getX() {
                return x;
            }
            public void setX(int x) {
                this.x = x;
            }
            public int getY() {
                return y;
            }
            public void setY(int y) {
                this.y = y;
            }
            public double getDistant(){
                return getDistant(0,0);
            }
            public double getDistant(int x, int y){
                int x1 = this.x-x;
                int y1 = this.y - y;
                return Math.sqrt(x1*x1 + y1*y1);
            }
            public String toString(){
                return "x="+x+",y="+y;
            }
        }

        System.out.println("常規方式:");
        Point ox = new Point(3,4);
        System.out.println(ox);
        System.out.println("1111result="+ox.getDistant());
        System.out.println("1111result="+ox.getDistant(5,8));

        System.out.println("反射方式:");
        //Class clazz = Point.class;
        Class clazz = Class.forName("com.yuqiaotech.simplejee.javase.reflect.ReflectSample$1Point");
        System.out.println("獲取Point類的構造函數對象，使用該對象得到一個Point類的實例");
        //獲取代表這個構造函數的對象public Point(int x, int y)
        Constructor c = clazz.getConstructor(int.class, int.class);
        Object[] args = new Object[] {3, 4};
        //Point o = new Point(3,4);
        Object o = c.newInstance(args);
        System.out.println(o);
        System.out.println("調用上述代碼得到的實例的public double getDistant()方法，並執行它");
        //public double getDistant()
        Method m = clazz.getMethod("getDistant", null);
        //Double result = o.getDistant();
        Double result = (Double)m.invoke(o, null);
        System.out.println("result="+result);
        System.out.println("調用上述代碼得到的實例的public double getDistant(int x, int y)方法，" +
                "並執行getDistant(5,8)");
        //public double getDistant(int x, int y)
        Method m2 = clazz.getMethod("getDistant", new Class[]{int.class,int.class});
        //Double result2 = o.getDistant(5,8);
        Double result2 = (Double)m2.invoke(o, new Integer[]{5,8});
        System.out.println("result2="+result2);
    }
}