public class User { private String name; public User(){ System.out.println("User的无参构造"); } public String getName() { return name; } public void setName(String name) { this.name = name; } public void show(){ System.out.println("name:"+name); } }
<?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.xsd"> <bean id="user" class="com.xxc.pojo.User"> <property name="name" value="江南"/> </bean> </beans>
public class MyTest { @Test public void test(){ ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml"); User user = (User) context.getBean("user"); user.show(); } }
说明:结果可以发现,在调用show方法之前,User对象已经通过无参构造初始化了。
public class UserT { private String name; public UserT(){ System.out.println("UserT的无参构造"); } public UserT(String name){ this.name = name; System.out.println("UserT的有参构造"); } public String getName() { return name; } public void setName(String name) { this.name = name; } public void show(){ System.out.println("name:"+name); } }
<!-- 第一种根据index参数下标设置 --> <bean id="userT" class="com.xxc.pojo.UserT"> <!-- index指构造方法 , 下标从0开始 --> <constructor-arg index="0" value="江南1"/> </bean>
<!-- 第二种根据参数类型设置 --> <bean id="userT" class="com.xxc.pojo.UserT"> <constructor-arg type="java.lang.String" value="江南2"/> </bean>
<!-- 第三种根据参数名字设置 --> <bean id="userT" class="com.xxc.pojo.UserT"> <!-- name指参数名 --> <constructor-arg name="name" value="江南3"/> </bean>
public class MyTest { @Test public void test(){ ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml"); UserT user = (UserT) context.getBean("userT"); user.show(); } }
结论:这里对于无参构造的user一直存在,说明在配置文件加载的时候。其中管理的对象都已经初始化了!就好比spring是一个婚介所,只要注册,那么信息就在婚介所中了,别人想看,只需要调取就可以。