其实注入null空值很简单，但偏偏总有人写不对，下面写一个简单的小实例
实体类：
public class PersonServiceBean {
	private String name;
	private String sex;
	private Integer age;
	private Date birth;
	public PersonServiceBean() {
		super();
		// TODO Auto-generated constructor stub
		System.out.println("构造器初始化对象");
	}
	public PersonServiceBean(String name,String sex,Integer age,Date birth) {
		super();
		this.name = name;
		this.sex = sex;
		this.age = age;
		this.birth = birth;
	}
	public void setName(String name) {
		System.out.println("name的set方法------------"+name);
		this.name = name;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	public void setAge(Integer age) {
		this.age = age;
	}
	public void setBirth(Date birth) {
		this.birth = birth;
	}
	@Override
	public String toString() {
		return "PersonServiceBean [name=" + name + ",sex=" + sex + ",age="
				+ age + ",birth=" + birth + "]";
	}
}
Xml文件
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
	<bean id="personServiceBean" class="cn.csdn.hr.service.PersonServiceBean">
		<property name="birth">
			<null></null>
		</property>
	</bean>
</beans>
这样就可以了，但是偏偏有人总是在<property name="birth">
中加上一个value=”null”，就是想不起来有一个null标签，要说的是如果不写<property name="XXX"></property>，注入的也会是空值哟
测试方法
	@Test
	public void test() {
		//第一步：获取应用程序上下文对象
		ApplicationContext ac=new ClassPathXmlApplicationContext("classpath:beanNull.xml");
		//第二步：根据应用程序上下文对象的getBean(id名称)方法获取实例bean对象
		PersonServiceBean p=(PersonServiceBean) ac.getBean("personServiceBean");
		System.out.println(p.toString());
	}
结果:
构造器初始化对象
PersonServiceBean [name=null,sex=null,age=null,birth=null]