[转]BeanUtils.copyProperties()的用法

原文地址： http://blog.youkuaiyun.com/itmyhome/article/details/7011656
BeanUtils提供对Java反射和自省API的包装。其主要目的是利用反射机制对JavaBean的属性进行处理。我们知道，一个JavaBean通常包含了大量的属性，很多情况下，对JavaBean的处理导致大量get/set代码堆积，增加了代码长度和阅读代码的难度。
下面通过代码来理解BeanUtils
首先创建两个类
Person.java

package com.org;  

import java.util.Date;  

public class Person {  
    private String name;  
    private String sex;  
    private int age;  
    private Date birthday;  

    public String getName() {  
        return name;  
    }  

    public void setName(String name) {  
        this.name = name;  
    }  

    public String getSex() {  
        return sex;  
    }  

    public void setSex(String sex) {  
        this.sex = sex;  
    }  

    public int getAge() {  
        return age;  
    }  

    public void setAge(int age) {  
        this.age = age;  
    }  

    public Date getBirthday() {  
        return birthday;  
    }  

    public void setBirthday(Date birthday) {  
        this.birthday = birthday;  
    }  


}  

Student.java

package com.org;  

import java.util.Date;  

public class Student {  
    private String name;  
    private int age;  
    private String address;  
    private Date birthday;  

    public String getName() {  
        return name;  
    }  
    public void setName(String name) {  
        this.name = name;  
    }  
    public int getAge() {  
        return age;  
    }  
    public void setAge(int age) {  
        this.age = age;  
    }  
    public String getAddress() {  
        return address;  
    }  
    public void setAddress(String address) {  
        this.address = address;  
    }  
    public Date getBirthday() {  
        return birthday;  
    }  
    public void setBirthday(Date birthday) {  
        this.birthday = birthday;  
    }  


}  

测试类 BeanUtilTest.java

package com.org;  

import java.lang.reflect.InvocationTargetException;  
import java.util.Date;  

//import com.sun.org.apache.commons.beanutils.BeanUtils;  

import org.apache.commons.beanutils.BeanUtils;  

public class BeanUtilTest {  
    public static void main(String[] args) {  
        Person per = new Person();  
        Student stu = new Student();  

        per.setName("zhangsan");  
        per.setSex("男");  
        per.setAge(20);  
        per.setBirthday(new Date());  

        stu.setName("wuangwu");  
        stu.setAddress("北京市");  
        try {  
            BeanUtils.copyProperties(stu, per);  

        } catch (IllegalAccessException e) {  
            // TODO Auto-generated catch block  
            e.printStackTrace();  
        } catch (InvocationTargetException e) {  
            // TODO Auto-generated catch block  
            e.printStackTrace();  
        }  
        System.out.println(stu.getName());  
        System.out.println(stu.getAge());  
        System.out.println(stu.getAddress());  
        System.out.println(stu.getBirthday());  

    }  
} 

程序输出结果为：

zhangsan  
20  
北京市  
Fri Nov 25 13:03:29 CST 2011 

可见Student自己设置的值都被Person给覆盖了
再做下面两个测试
把Person中的setName和setAge 改为setname setage程序输出结果为

zhangsan  
20  
北京市  
Fri Nov 25 13:08:34 CST 2011  

结果没有改变
而如果改为setNAme, setAGe结果为：

wuangwu  
0  
北京市  
Fri Nov 25 13:10:25 CST 2011  

我们发现结果改变了 内容没有被覆盖
注： 当我们加载BeanUtils类时 可能会报如下错误

Exception in thread "main" java.lang.ExceptionInInitializerError  
    at com.org.BeanUtilTest.main(BeanUtilTest.java:101)  
Caused by: com.sun.org.apache.commons.logging.LogConfigurationException: com.sun.org.apache.commons.logging.LogConfigurationException: java.lang.NullPointerException (Caused by java.lang.NullPointerException) (Caused by com.sun.org.apache.commons.logging.LogConfigurationException: java.lang.NullPointerException (Caused by java.lang.NullPointerException))  
    at com.sun.org.apache.commons.logging.impl.LogFactoryImpl.newInstance(LogFactoryImpl.java:543)  
    at com.sun.org.apache.commons.logging.impl.LogFactoryImpl.getInstance(LogFactoryImpl.java:235)  
    at com.sun.org.apache.commons.logging.impl.LogFactoryImpl.getInstance(LogFactoryImpl.java:209)  
    at com.sun.org.apache.commons.logging.LogFactory.getLog(LogFactory.java:351)  
    at com.sun.org.apache.commons.beanutils.BeanUtils.<clinit>(BeanUtils.java:111)  
    ... 1 more  
Caused by: com.sun.org.apache.commons.logging.LogConfigurationException: java.lang.NullPointerException (Caused by java.lang.NullPointerException)  
    at com.sun.org.apache.commons.logging.impl.LogFactoryImpl.getLogConstructor(LogFactoryImpl.java:397)  
    at com.sun.org.apache.commons.logging.impl.LogFactoryImpl.newInstance(LogFactoryImpl.java:529)  
    ... 5 more  
Caused by: java.lang.NullPointerException  
    at com.sun.org.apache.commons.logging.impl.LogFactoryImpl.getLogConstructor(LogFactoryImpl.java:374)  
    ... 6 more  

产生错误的原因是引入的包不对，应引入import org.apache.commons.beanutils.BeanUtils;
而不应是import com.sun.org.apache.commons.beanutils.BeanUtils;
另外所需jar包为：
commons-beanutils-1.8.3.jar
commons-logging-1.1.1.jar
还有一个很邪门的问题 实在令我不解
就是如果把Person，Student 测试类写在一起的话 会产生问题
类似与这样的结构

class Person{  
    .....  
}  
class Student{  
    .....  
}  

public class BeanUtilTest {  
    public static void main(String[] args) {  
        ......  
    }  
}  

出现不了我们所需要的结果，郁闷中....