尚学堂 212反射机制（动态操作、构造器、方法、属性、合并文件）

package com.bjsxt.test.bean;

public class User {
    
    private int id;
    private int age;
    private String uname;
    
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getUname() {
        return uname;
    }
    
    public void setUname(String uname) {
        this.uname = uname;
    }
    
    public void setUname() {
        this.uname = "高淇";
    }
    
    public User(int id, int age, String uname) {
        super();
        this.id = id;
        this.age = age;
        this.uname = uname;
    }
    
    //javabean必须要有无参的构造方法！
    public User() {
    }
}

package com.bjsxt.test;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

/**
 * 应用反射的API，获取类的信息(类的名字、属性、方法、构造器等)
 * @author 尚学堂高淇  www.sxt.cn
 *
 */
public class Demo02 {
    public static void main(String[] args) {
        String path = "com.bjsxt.test.bean.User";
        
        try {
            Class clazz = Class.forName(path);
            
            //获取类的名字
            System.out.println(clazz.getName());//获得包名+类名：com.bjsxt.test.bean.User
            System.out.println(clazz.getSimpleName());    //获的类名：User
            
            //获取属性信息
//            Field[] fields = clazz.getFields(); //只能获得public的field
            Field[] fields = clazz.getDeclaredFields();//获得所有的field
            Field f = clazz.getDeclaredField("uname");
            System.out.println(fields.length);
            for(Field temp:fields){
                System.out.println("属性："+temp);
            }
            //获取方法信息
            Method[] methods = clazz.getDeclaredMethods();
            Method m01 = clazz.getDeclaredMethod("getUname", null);
            //如果方法有参，则必须传递参数类型对应的class对象
            Method m02 = clazz.getDeclaredMethod("setUname", String.class); 
            for(Method m:methods){
                System.out.println("方法："+m);
            }
            
            //获得构造器信息
            Constructor[] constructors = clazz.getDeclaredConstructors();
            Constructor c = clazz.getDeclaredConstructor(int.class,int.class,String.class);
            System.out.println("获得构造器："+c);
            for(Constructor temp:constructors){
                System.out.println("构造器："+temp);
            }
            
            
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

程序的运行结果是：

com.bjsxt.test.bean.User
User
3
属性：private int com.bjsxt.test.bean.User.id
属性：private int com.bjsxt.test.bean.User.age
属性：private java.lang.String com.bjsxt.test.bean.User.uname
方法：public int com.bjsxt.test.bean.User.getId()
方法：public java.lang.String com.bjsxt.test.bean.User.getUname()
方法：public void com.bjsxt.test.bean.User.setUname()
方法：public void com.bjsxt.test.bean.User.setUname(java.lang.String)
方法：public void com.bjsxt.test.bean.User.setId(int)
方法：public void com.bjsxt.test.bean.User.setAge(int)
方法：public int com.bjsxt.test.bean.User.getAge()
获得构造器：public com.bjsxt.test.bean.User(int,int,java.lang.String)
构造器：public com.bjsxt.test.bean.User()
构造器：public com.bjsxt.test.bean.User(int,int,java.lang.String)

package com.bjsxt.test;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;

import com.bjsxt.test.bean.User;

/**
 * 通过反射API动态的操作：构造器、方法、属性
 * @author 尚学堂高淇 www.sxt.cn
 *
 */
public class Demo03 {
    public static void main(String[] args) {

        String path = "com.bjsxt.test.bean.User";
        
        try {
            Class<User> clazz = (Class<User>) Class.forName(path);
            
            //通过反射API调用构造方法，构造对象
            User u = clazz.newInstance();    //其实是调用了User的无参构造方法
            System.out.println(u);
            
            Constructor<User> c = clazz.getDeclaredConstructor(int.class,int.class,String.class);
            User u2 = c.newInstance(1001,18,"高淇二");
            System.out.println(u2.getUname());
            
            //通过反射API调用普通方法
            User u3 = clazz.newInstance();
            Method method = clazz.getDeclaredMethod("setUname", String.class);
            method.invoke(u3, "高淇三");   //u3.setUname("高淇三");
            System.out.println(u3.getUname());
            
            //通过反射API操作属性
            User u4 = clazz.newInstance();
            Field f = clazz.getDeclaredField("uname");
            f.setAccessible(true); //这个属性不需要做安全检查了，可以直接访问
            f.set(u4, "高淇四");        //通过反射直接写属性
            System.out.println(u4.getUname());    //通过反射直接读属性的值
            System.out.println(f.get(u4));
            
            
        } catch (Exception e) {
            e.printStackTrace();
        }
    
        
    }
}

程序的运行结果是：

com.bjsxt.test.bean.User@5cb08ba7
高淇二
高淇三
高淇四
高淇四

注意对应User类的private属性的成员变量和方法，外部进行反射需要赋值的时候需要f.setAccessible(true); 设置成true，表示允许外部进行访问