Spring的@Required注解

该@Required注解适用于bean属性setter方法，并表示受影响的bean属性必须在XML配置文件在配置时进行填充。否则，容器会抛出一个BeanInitializationException异常。

例子：

pom.xml：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

  <modelVersion>4.0.0</modelVersion>

  <groupId>com.jsoft.testspring</groupId>

  <artifactId>testannotationrequired</artifactId>

  <version>0.0.1-SNAPSHOT</version>

  <packaging>jar</packaging>

  <name>testannotationrequired</name>

  <url>http://maven.apache.org</url>

  <properties>

    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

  </properties>

  <dependencies>

    <dependency>

      <groupId>junit</groupId>

      <artifactId>junit</artifactId>

      <version>3.8.1</version>

      <scope>test</scope>

    </dependency>

    <!-- Spring Core -->

    <!-- http://mvnrepository.com/artifact/org.springframework/spring-core -->

    <dependency>

        <groupId>org.springframework</groupId>

        <artifactId>spring-core</artifactId>

        <version>4.1.4.RELEASE</version>

    </dependency>

    <!-- Spring Context -->

    <!-- http://mvnrepository.com/artifact/org.springframework/spring-context -->

    <dependency>

        <groupId>org.springframework</groupId>

        <artifactId>spring-context</artifactId>

        <version>4.1.4.RELEASE</version>

    </dependency>

  </dependencies>

</project>

Student.java：

package com.jsoft.testspring.testannotationrequired;

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

public class Student {

    private Integer age;

    private String name;

    @Required

    public void setAge(Integer age){

        this.age = age;

    }

    public Integer getAge(){

        return this.age;

    }

    public void setName(String name){

        this.name = name;

    }

    public String getName(){

        return this.name;

    }

}

beans.xml：

<?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: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">

   <context:annotation-config/>

   <bean id="student" class="com.jsoft.testspring.testannotationrequired.Student">

        <property name="name" value="Jim"/>

   </bean>

</beans>

App.java：

package com.jsoft.testspring.testannotationrequired;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

/**

 * Hello world!

 *

 */

public class App

{

    public static void main( String[] args )

    {

           ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");

           Student student = (Student)applicationContext.getBean("student");

           System.out.println(student.getAge());

           System.out.println(student.getName());

    }

}

而此时的运行结果是出现了错误的，因为age的setter方法没有在bean中注入，而age的setter方法标记了@Required，也就是必须要输入，抛出的异常为：BeanInitializationException。

那么我们将beans.xml补全之后：

<?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: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">

   <context:annotation-config/>

   <bean id="student" class="com.jsoft.testspring.testannotationrequired.Student">

        <property name="name" value="Jim"/>

        <property name="age" value="27"/>

   </bean>

</beans>

此时的运行结果一切正常：

巴特西

Spring的@Required注解

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