Spring ClassPathXmlApplicationContext getBean创建实例

之前接触的项目大都是以spring注解来进行开发，用到的配置文件加载完也没太过在意spring bean的创建。测试代码如下：

@Test
public void testD(){
ApplicationContext context = new ClassPathXmlApplicationContext("test/extendbean/applicationContext.xml");
ParentBean parentBean = (ParentBean)context.getBean("parentBean");
System.out.println(parentBean.getStr());
ParentBean parentBean2 = (ParentBean)context.getBean("parentBean");
}

ParentBean.java如下：

package test.extendbean;

public class ParentBean {

private static String str;

private int intNum;

/**
*
*/
public ParentBean() {
System.out.println("-----------------------");
}

public int getIntNum() {
return intNum;
}

public void setIntNum(int intNum) {
this.intNum = intNum;
}

public String getStr() {
return str;
}

public void setStr(String str) {
this.str = str;
}

public void init(){
System.out.println("---------------");
}

}

applicationContext.xml代码：

<pre name="code" class="html"><?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:aop="http://www.springframework.org/schema/aop"
default-lazy-init="true"
xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.0.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
">

<bean id="config"
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="locations">
<list>
<value>file:/app/config/test.properties</value>
</list>
</property>
</bean>

<bean id="parentBean" class="test.extendbean.ParentBean">
<property name="str" value="${ParentBean.str}" />
<property name="intNum" value="${ParentBean.intNum}"/>
</bean>

</beans>

在ParentBean的无参构造器，和set方法中均打上断点，debug运行Test方法，此时就会发现，在

new ClassPathXmlApplicationContext("test/extendbean/applicationContext.xml")的时候并未进入debug视图，在getBean()时才进入，debug跟了getBean()发现如下截图，spring管理的bean均被放在一个ConcurrentHashMap中，所以在getBean()时才进行了初始化，再次执行getBean()则不会再创建实例。



另外，之所以是在getBean()时创建实例，是因为在配置文件中有default-lazy-init="true"这个属性，默认为false，即在加载配置文件的时候创建实例