@Autowired vs @Required on setter [英] @Autowired vs @Required on setter

问题描述

我很想知道这样的代码有什么区别：

I'm curious to know what's the difference between code like this:

class MyClass {
   @Autowired
   MyService myService;
}

和这样的代码：

class MyClass {
   MyService myService;

   @Required
   public void setMyService(MyService val) {
       this.myService = val;
   }
}

推荐答案

<当您想要自动装配bean时，使用code> @Autowired 注释。 @Autowired 不限于setter。它也可以与构造函数和字段一起使用。如果您在字段上使用 @Autowired 注释，该字段将使用具有匹配数据类型的bean自动装配。

@Autowired annotation is used when you want to autowire a bean. @Autowired is not limited to setter. It can be used with a constructor and a field as well. If you use @Autowired annotation on a field, that field will be autowired with bean having matching data type.

@Required 检查是否已设置特定属性。如果字段已使用 @Required 注释进行注释，并且未设置该字段，则将获得 org.springframework.beans.factory.BeanInitializationException 。

@Required checks if a particular property has been set or not. If a field has been annotated with @Required annotation and that field is not set, you will get org.springframework.beans.factory.BeanInitializationException.

参考：

Spring @Autowired usage

Spring的@Required注释的推荐用法

编辑：正如'kryger'指出：用 @Autowired 注释的字段实际上也是 @Required （除非你明确地将其参数设置为false）。
例如：

As pointed by 'kryger': field annotated with @Autowired is effectively also @Required (unless you explicitly set its parameter required to false). eg:

@Autowired(required=false)
private ObjectType objectType;

对于已注释的字段 @Autowired ，如果具有匹配数据类型的bean不可用，则抛出 org.springframework.beans.factory.BeanCreationException 。

For a field that has been annotated @Autowired, if bean with matching data type in not available, org.springframework.beans.factory.BeanCreationException is thrown.

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