基于Xml方法的Bean的配置-实例化Bean的方法-构造方法

news2024/11/17 2:46:55

SpringBean的配置详解

Bean的实例化配置

Spring的实例化方法主要由以下两种

构造方法实例化：底层通过构造方法对bean进行实例化

构造方法实例化bean又分为无参方法实例化和有参方法实例化，在Spring中配置的<bean>几乎都是无参构造该方式，在此处不赘述。下面讲解有参构造方法实例化Bean

在配置文件中为有参构造方法中的参数指定值

<?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="userService" class="com.example.Service.Impl.UserServiceImpl">
        <constructor-arg name="name" value="hahaha"></constructor-arg>
        <property name="userDAO" ref="userDAO"></property>
    </bean>
    <bean id="userDAO" class="com.example.DAO.UserDAO"></bean>
</beans>

package com.example.Service.Impl;

import com.example.DAO.UserDAO;
import com.example.Service.UserService;


public class UserServiceImpl implements UserService {
    // todo 无参构造方法
    public UserServiceImpl() {
        System.out.println("无参构造方法");
    }

    // todo 有参构造方法
    public UserServiceImpl(String name) {
        System.out.println("有参构造方法");
        System.out.println(name);
    }

    private UserDAO userDAO;

    public void setUserDAO(UserDAO userDAO) {
    }

}

测试类运行结果

package com.example.Test;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class TestApplicationContext {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("application.xml");
        Object userService1 = context.getBean("userService");
        System.out.println(userService1);
        context.close();

    }
}