Spring 创建bean的几种方式

在XML配置文件中，通过bean标签创建bean，然后再通过spring容器进行管理

创建xml配置文件定义bean

一、通过构造函数创建

1 <?xml version="1.0" encoding="UTF-8"?>
2 <beans xmlns="http://www.springframework.org/schema/beans"
3        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
4        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
5 
6     <bean id="User" class="com.example.springioc.User"/>
7 </beans>

创建bean类

1 public class User {
2     public void test(){
3         System.out.println("我是bean");
4     }
5 }

通过创建容器对象来读取配置文件，这部分代码与后面的代码一样。

ApplicationContext context = new ClassPathXmlApplicationContext("appContext.xml");
        User user = (User) context.getBean("User");
        user.test();

二、通过静态工厂创建

创建静态工厂

public class UserFactory {
    private static final User user = new User();
    public static User getUser(){
        return user;
    }
}

创建工厂bean，这里的factory-method就是获取User的对象的静态方法

<?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="UserFactory" class="com.example.springioc.UserFactory" factory-method="getUser"/>
</beans>

三、通过实例工厂创建

使用实例方法创建对象

1 public class UserFactory {
2     private static  User user = new User();
3     public  User getUser(){
4         return user;
5     }
6 }

XML创建工厂bean。然后调用工厂非静态方法创建新的bean

1 <?xml version="1.0" encoding="UTF-8"?>
2 <beans xmlns="http://www.springframework.org/schema/beans"
3        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
4        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
5 
6     <bean id="UserFactory" class="com.example.springioc.UserFactory" />
7     <bean id="User" factory-bean="UserFactory" factory-method="getUser"></bean>
8 </beans>