Spring @Required注释

@Required注解适用于bean属性的setter方法并且它指示，受影响的bean属性必须在配置时被填充在XML配置文件中，否则容器将抛出BeanInitializationException例外。下面是一个例子，说明使用@ Required注解。

例子:

我们使用Eclipse IDE，然后按照下面的步骤来创建一个Spring应用程序：

步骤描述1Create a project with a name SpringExample and create a package com.yiibai under the src folder in the created project.2Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter.3Create Java classes Student and MainApp under the com.yiibai package.4Create Beans configuration file Beans.xml under the src folder.5The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below.

这里是Student.java文件的内容：

package com.yiibai;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：

package com.yiibai;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中的内容：

<?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.yiibai.Student">      <property name="name"  value="Zara" />      <!-- try without passing age and check the result -->      <!-- property name="age"  value="11"-->   </bean></beans>

一旦创建源代码和bean配置文件完成后，让我们运行应用程序。如果一切顺利，这将抛出BeanInitializationException异常，并与其他日志信息打印以下错误：

Property 'age' is required for bean 'student'

接下来，可以从“age”属性中删除注释如下尝试后，上面的例子：

<?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.yiibai.Student">      <property name="name"  value="Zara" />      <property name="age"  value="11"/>   </bean></beans>

现在，上面的例子会产生以下结果：

Name : ZaraAge : 11

标签：Spring    @Required    注释    @Required        

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