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：
测试工程：https://github.com/easonjim/5_java_example/tree/master/springtest/test12/testannotationrequired
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