Spring @Required 注解

Spring 基于注释的配置

@Required 注释适用于 bean 属性设置器方法，它表明受影响的 bean 属性必须在配置时填充到 XML 配置文件中。 否则，容器会抛出 BeanInitializationException 异常。 下面是一个例子来展示@Required 注解的使用。

示例

在 com.jiyik 包下创建 Java 类 Student 和 MainApp。

这是 Student.java 文件的内容

Student.java

package com.jiyik;

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 age;
   }
   
   @Required
   public void setName(String name) {
      this.name = name;
   }
   public String getName() {
      return name;
   }
}

以下是 MainApp.java 文件的内容

MainApp.java

package com.jiyik;

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

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");
      
      Student student = (Student) context.getBean("student");
      System.out.println("Name : " + student.getName() );
      System.out.println("Age : " + student.getAge() );
   }
}

以下是配置文件Beans.xml的内容

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-3.0.xsd
   http://www.springframework.org/schema/context
   http://www.springframework.org/schema/context/spring-context-3.0.xsd">

   <context:annotation-config/>

   <!-- Definition for student bean -->
   <bean id = "student" class = "com.jiyik.Student">
      <property name = "name" value = "Zara" />

      <!-- try without passing age and check the result -->
      <!-- property name = "age"  value = "11"-->
   </bean>

</beans>

完成源代码和 bean 配置文件后，让我们运行应用程序。 如果应用程序一切正常，它将引发 BeanInitializationException 异常并打印以下错误以及其他日志消息

Property 'age' is required for bean 'student'

接下来，可以在从 'age' 属性中删除评论后尝试上面的示例，如下所示

<?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-3.0.xsd
   http://www.springframework.org/schema/context
   http://www.springframework.org/schema/context/spring-context-3.0.xsd">

   <context:annotation-config/>

   <!-- Definition for student bean -->
   <bean id = "student" class = "com.jiyik.Student">
      <property name = "name" value = "Zara" />
      <property name = "age"  value = "11"/>
   </bean>

</beans>

打印结果如下所示

Name : Zara
Age : 11

Spring 基于注释的配置