SpringFramework｜@Required的使用

@Required的使用

前述

Java: 1.8

Maven: 3

SpringFramework版本以及各组件成员: 5.1.1.RELEASE

• spring-context
• spring-core
• spring-beans

@Required注释适用于bean属性setter方法, 再经过在bean定义或经过自动装配一个明确的属性值:

Required意为"须要", 它代表受影响的 bean 属性在配置时必须放在 XML 配置文件中，不然容器就会抛出一个 BeanInitializationException 异常。

public class SimpleMovieLister {

    private MovieFinder movieFinder;

    @Required
    public void setMovieFinder(MovieFinder movieFinder) {
        this.movieFinder = movieFinder;
    }

    // ...
}

@Required将在之后的版本弃用.

示例

TestBean.java - 一个Bean(这不是一个规范的JavaBean, 顺口而叫的):

package noioo;


import org.springframework.beans.factory.annotation.Required;

public class TestBean {

    private String theValue;

    public String getTheValue() {
        return theValue;
    }

    @Required  // 用在set上面
    public void setTheValue(String theValue) {
        this.theValue = theValue;
    }
}

在spring-beans.xml中启用注解.

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:content="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">

    <content:annotation-config/>

    <bean id="testBean" class="noioo.TestBean">
        <property name="theValue" value="Hello, World"/>
    </bean>
</beans>

执行者 - Runner.java

package noioo;

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

public class Runner {

    public static void main(String[] args){
        ApplicationContext context = new ClassPathXmlApplicationContext("spring-beans.xml");
        TestBean testBean = (TestBean)context.getBean("testBean");
        System.out.println(testBean.getTheValue());
    }
}

执行结果

Hello, World

Process finished with exit code 0