Java反射

Java的反射非常强大，传递class， 可以动态的生成该类、取得这个类的所有信息，包括里面的属性、方法以及构造函数等，甚至可以取得其父类或父接口里面的内容。

  obj.getClass().getDeclaredMethods();//取得obj类中自己定义的方法， 包括私有的方法。

  obj.getClass().getMethods();//取得obj类中自己定义的方法及继承过来的方法， 但私有方法得不到。

  同样， 对field也是一样，obj.getClass().getDeclaredFields();取得的是这个类中所有的属性，包括私有的field; 对obj.getClass().getFields();//取得是自己以及接继承来的属性， 但不能取得自己的私有属性。

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();
  }

 

评论

2 楼 ynstudio 2010-02-10  

再来一个

package com.yuqiaotech.simplejee.javase.reflect;

import java.beans.BeanInfo;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
/**
 * 使用BeanInfo来设置和读取对象的属性。
 */
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);
		}
	}
}

1 楼 ynstudio 2010-02-10  

呵呵，来个狗尾

package com.yuqiaotech.simplejee.javase.reflect;

import java.lang.reflect.*;
/**
 * 1、获取类的相关信息
 * 2、知道类名，实例化出对象
 * 3、动态调用实例的方法
 * 
 *
 */
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("常规方式:");
		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("获取Point类的构造函数对象，使用该对象得到一个Point类的实例");
		//获取代表这个构造函数的对象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("调用上述代码得到的实例的public double getDistant()方法，并执行它");
		//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("调用上述代码得到的实例的public double getDistant(int x, int y)方法，" +
				"并执行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);
	}
}