Spring 实例化Bean的基本方法

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三种基本实例化Bean方法

  • 构造器实例化
  • 静态工厂实例化
  • 实例化工厂实例化
测试用业务类
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package com.example.service;

public class UserService {
    public void test(){
        System.out.println("UserService ...");
    }
}
测试
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package com.example;

import com.example.service.UserService;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class App 
{
    public static void main( String[] args )
    {

        ApplicationContext ac = new ClassPathXmlApplicationContext("application.xml");
        UserService userService = ac.getBean("userService", UserService.class);
        userService.test();
    }
}

构造器实例化Bean

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<?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
        https://www.springframework.org/schema/beans/spring-beans.xsd">

  <bean id="userService" class="com.example.service.UserService"/>
</beans>

静态工厂实例化Bean

  • 要有工厂类和工厂方法，工厂方法负责创建实体类
  • 工厂方法为静态方法
静态工厂
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package com.example.factory;

import com.example.service.UserService;

/**
 * 静态工厂类
 */
public class StaticFactory {

    // 创建Bean的静态方法
    public static UserService createUserService(){
        return new UserService();
    }
}

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<?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
        https://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="userService" class="com.example.factory.StaticFactory" factory-method="createUserService"/>
</beans>

实例化工厂创建Bean

  • 工厂方法为非静态方法
  • 需要配置工厂Bean，并在业务bean中配置 factory-bean， factory-method 属性
实例化工厂
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package com.example.factory;

import com.example.service.UserService;

/**
 * 实例化工厂类
 */
public class InstanceFactory {
    public UserService createUserService(){
        return new UserService();
    }
}
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<?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
        https://www.springframework.org/schema/beans/spring-beans.xsd">


    <bean id="instanceFactory" class="com.example.factory.InstanceFactory"/>
    <bean id="userService" factory-bean="instanceFactory" factory-method="createUserService"/>
</beans>