BeanUtils.copyProperties()的用法

原文出处：http://blog.csdn.net/itmyhome1990/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....

 

 

 

读者回复：刚debug完，原因我知道了，主要是属性copy时候，会判断这个方法是否可读，如果方法不可读则不进行属性拷贝，java中如果类不是public的，那么方法就是readable的，所以copy不了，这个你debug一下就会发现。的确挺恶心。