BeanUtils copyProperties 的用法

               

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：

zhangsan20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

zhangsan20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：

wuangwu0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 moreCaused 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 moreCaused 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....