Spring入门——IOC

Posted 2020-11-24 Howlet

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1. IOC定义

Inversion of Control，减低计算机代码间的耦合度，对象的创建交给外部容器完成，不用再new了

2. 流程

2.1 创建Bean对象

package bean;

public class User {
    
    private String name;
    private String email;
    private String password;
    
    /**
    * 省略了getters/setters
    * @author Howl
    */
    
    //构造函数
    public User(String name, String email, String password) {
        super();
        this.name = name;
        this.email = email;
        this.password = password;
    }
}

2.2 配置applicationContext.xml

<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"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
    <!-- 上面是约束的固定写法 -->
    
    
    <!-- 配置Bean对象给Spring容器 -->
    <!-- id 唯一表示 -->
    <!-- class 对应的Bean对象 -->
    <!-- scope 作用域，单例和多例 -->
    <bean id="User" class="bean.User" scope="singleton"></bean>
    
</beans> 

2.3 通过容器获取Bean对象

//通过配置文件获取上下文
applicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
//通过上下文获取Bean对象，不用通过new方式了
User user = ac.getBean("User");

3. 其他细节

3.1 带参构造函数创建对象

<bean id="User" class="bean.User" scope="singleton">
    
    <!--constructor指定构造函数的参数类型、名称、第几个-->
    <constructor-arg index="0" name="name" type="String" value="Howl"></constructor-arg>
    <!--参数为对象时，value改为ref="" -->
</bean>

3.2 装载集合

<bean id="userService" class="bb.UserService" >
    <constructor-arg >
        <list>
            //普通类型
            <value></value>
            //引用类型
            <ref></ref>
        </list>
    </constructor-arg>
</bean>

3.3 注解

1.先引入context名称空间
xmlns:context="http://www.springframework.org/schema/context"

2.开启注解扫描器
<context:component-scan base-package=""></context:component-scan>

3.在Bean对象中添加@Component(name ="User"),就不用在配置文件中写<Bean>标签了