Spring之BeanFactory与ApplicationContext区别

定义两个bean分别为Bean1和Bean2

Bean1.java

package com.itmyhome.bean;

public class Bean1 {
	private String name;
	private int age;
	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;
	}
	
}

Bean2.java

package com.itmyhome.bean;

public class Bean2 {
	private String name;
	private String sex;
	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;
	}
	
}

applicationContext.xml配置文件

把Bean1和Bean2配置到xml文件中

 <bean id="bean1" class="com.itmyhome.bean.Bean1">
          <property name="name" value="zhangsan" />
          <property name="age" value="21" />
      </bean>
      <!-- 此处的class路径是错误的，没有Bean3这个类 -->     
      <bean id="bean2" <span style="color: #ff0000;">class="com.itmyhome.bean.Bean3">
</span>           <property name="name" value="lisi" />
           <property name="sex" value="男" />
      </bean>    

进行测试

使用XmlBeanFactory

public class Client {
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		XmlBeanFactory factory = new XmlBeanFactory(new FileSystemResource("src/applicationContext.xml"));
		
		Bean1 bean1 = (Bean1)factory.getBean("bean1");
	    System.out.println("bean1.name: "+bean1.getName());
	    System.out.println("bean1.age: "+bean1.getAge());
	}
}

观察结果 可以运行通过

接下来使用ApplicationContext

public class Client {

	public static void main(String[] args) {
		// TODO Auto-generated method stub	
		ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
		
		Bean1 bean1 = (Bean1)context.getBean("bean1");
	    System.out.println("bean1.name: "+bean1.getName());
	    System.out.println("bean1.age: "+bean1.getAge());
	}

}

结果报异常

Exception in thread "main" org.springframework.beans.factory.CannotLoadBeanClassException: Cannot find class [com.itmyhome.bean.Bean3] for bean with name 'bean2' defined in class path resource 

[applicationContext.xml]; nested exception is java.lang.ClassNotFoundException: com.itmyhome.bean.Bean3

我们在applicationContext.xml中配置了两个Bean,bean1和bean2 虽然bean2中找不到Bean3这个类，但我们getBean()的时候也没有用到bean2啊，为什么会报错呢？

原因是ApplicationContext和BeanFactory提供了不同的加载机制，ApplicationContext和BeanFacotry相比,提供了更多的扩展功能，但其主要区别在于后者是延迟加载,如果Bean的某一个属性没有注入，BeanFacotry加载后，直至第一次使用调用getBean方法才会抛出异常；而ApplicationContext则在初始化自身时检验，这样有利于检查所依赖属性是否注入；所以通常情况下我们选择使用ApplicationContext.

解决延迟加载的办法是在applicationContext.xml中<beans>标签中添加default-lazy-init="true"属性

<beans xmlns="http://www.springframework.org/schema/beans"
	     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	     xmlns:aop="http://www.springframework.org/schema/aop"
	     xmlns:tx="http://www.springframework.org/schema/tx"
	  <a href="http://www.springframework.org/schema/aop">http://www.springframework.org/schema/aop</a> http://www.springframework.org/schema/aop/spring-aop-2.0.xsd
           http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd" <span style="color: #ff0000;">default-lazy-init="true"></span>