Java中反射和内省代码实例

反射

我们建立一个Person类，对此进行反射操作。

package myReflection;

public class Person {
    private String name;
    private String id;
    Person(){}
    /**
     * @param name
     * @param id
     */
    public Person(String name, String id) {
        super();
        this.name = name;
        this.id = id;
    }
    /**
     * @return the name
     */
    public String getName() {
        return name;
    }
    /**
     * @param name the name to set
     */
    public void setName(String name) {
        this.name = name;
    }
    /**
     * @return the id
     */
    public String getId() {
        return id;
    }
    /**
     * @param id the id to set
     */
    public void setId(String id) {
        this.id = id;
    }
    
}

分别对constructor‘、属性和方法反射

test1====无参数构造函数

test2 ====有参数构造函数

test3=====属性

test4=====方法

package myReflection;

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

import org.junit.Test;

public class useReflection {

    public static void main(String[] args) throws ClassNotFoundException {
        // TODO Auto-generated method stub
        Class c1=Person.class;
        Class c2=new Person().getClass();
        Class c3=Class.forName("myReflection.Person");
        
    }
    @Test
    public void test4() throws Exception{
        Class c=Class.forName("myReflection.Person");
        Person p=(Person) c.newInstance();
        Method m=c.getDeclaredMethod("setName", String.class);
        
        m.invoke(p, "Lannister");
        System.out.println(p.getName());
    }
    @Test
    public void test3() throws Exception{
        try {
            Class c=Class.forName("myReflection.Person");
            Person p=(Person) c.newInstance();
            Field f1=c.getDeclaredField("name");
            f1.setAccessible(true);
            f1.set(p, "Stark");
            System.out.println(f1.get(p));
            
        } catch (Exception e) {
            // TODO: handle exception
        }
    }
    @Test
    public void test2() throws Exception
    {
        Class c=Class.forName("myReflection.Person");
        Constructor cs=c.getConstructor(String.class,String.class);
        Person p1=(Person)cs.newInstance("Jon","Snow");
        System.out.println(p1.getId()+" "+p1.getName());
    }
    @Test
    public void test1() throws Exception{
        Class cl3=Class.forName("myReflection.Person");
        Person p =(Person)cl3.newInstance();
        p.setName("Tully");
        System.out.println(p.getName());
    }
}

 内省

目的：将Map中的数据封装到一个JavaBean对象中去。

class User {
    private String username;
    private String password;

    public User(String username, String password) {
        this.username = username;
        this.password = password;
    }

    public User() {
    }

    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 toString() {
        return "User [username=" + username + ", password=" + password + "]";
    }

}



Map<String,String> map=new HashMap<String,String>();
        map.put("username", "admin");
        map.put("password", "admin123");
        BeanInfo bi=Introspector.getBeanInfo(User.class);
        PropertyDescriptor[] pds=bi.getPropertyDescriptors();
        User user=new User();
        for(PropertyDescriptor pd:pds) {
            String name=pd.getName();
            String value=map.get(name);
            System.out.println("name value pair "+name +": "+value);
            if(value!=null) {
                //wm write method
                Method wm=pd.getWriteMethod();
                wm.invoke(user, value);
            }
        }
        System.out.println(user.toString());

输出

name value pair class: null
name value pair password: admin123
name value pair username: admin
User [username=admin, password=admin123]

每个PropertyDescriptor对象对应一个JavaBean属性：

l  String getName()：获取JavaBean属性名称；

l  Method getReadMethod：获取属性的读方法；

l  Method getWriteMethod：获取属性的写方法。

使用commons-beanutils可以简化内省的操作

例子

设置属性

User user=new User();

BeanUtils.setProperty(user,"username","admin");

获取JavaBean属性

User user=new User("admin","12334");

String username=BeanUtils.getProperty(user,"username");

把Map数据封装到JavaBean对象中

Map<String,String> map=new HashMap<String,String>();
        map.put("username", "admin");
        map.put("password", "admin123");
User user=new User();
BeanUtils.populate(user,map);

等等