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：

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....

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原文地址：https://www.cnblogs.com/skiwnchqhh/p/10156017.html