BeanUtils.copyProperties()的用法详解编程语言

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….