Spring的@Required注释

  • Z时代
  • 2024-01-10
  • 分类：综合

本文内容纲要：Spring的@Required注释

大多数情况下，我们不必为Bean的所有属性设值，如果确保属性必须要设置，就使用@Required注解，标识在set方法上，检查属性是否设置有值。

/**
 ** @Required注解用来检查age属性是否有设置值
 */
public class Student {
  private String name;
  private int age;
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  public int getAge() {
    return age;
  }
  @Required
  public void setAge(int age) {
    this.age = age;
  }
}

仅仅只是使用@Required注解并不能起到依赖检查的效果，还需要注册一个RequiredAnnotationBeanPostProcessor，两种方式：

1.直接将RequiredAnnotationBeanPostProcessor注册成Bean

<bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor"/>

2.引入context:annotation-config配置，该配置包括AutowiredAnnotationBeanPostProcessor、CommonAnnotationBeanPostProcessor、PersistenceAnnotationBeanPostProcessor、RequiredAnnotationBeanPostProcessor

<?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"
  xmlns:aop="http://www.springframework.org/schema/aop"
  xsi:schemaLocation="http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.3.xsd
        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-4.3.xsd">
 <context:annotation-config />
 <bean id="Student" class="org.source.demo.Student">
  <property name="name" value="jack" />
 </bean>
</beans>

如果你的Student Bean中没有设置age属性的值，运行就会出错

Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanInitializationException: Property 'age' is required for bean 'Student'

自定义Required注释

如果你的项目中有自己的Required注释，Spring允许你自定义自己的注解，并可以注册到Spring中，相当于@Required

1.自定义注解

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface MyRequired {
}

2.注解应用到属性

public class Student {
  private String name;
  private int age;
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  public int getAge() {
    return age;
  }
  @MyRequired
  public void setAge(int age) {
    this.age = age;
  }
}

3.将注解注册到RequiredAnnotationBeanPostProcessor

<bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor">
   <property name="requiredAnnotationType" value="org.source.demo.MyRequired" />
 </bean>

这样就完成了自定义注解@MyRequired，相当于@Required

本文内容总结：Spring的@Required注释

原文链接：https://www.cnblogs.com/pzjtian/p/15328499.html

以上是 Spring的@Required注释 的全部内容， 来源链接： utcz.com/z/296251.html

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