Spring依赖检查bean 配置文件用于确定的特定类型(基本，集合或对象)的所有属性被设置。在大多数情况下，你只需要确保特定属性已经设置但不是所有属性..

对于这种情况，你需要 @Required 注解，请参见下面的例子：

@Required示例

Customer对象，适用@Required在 setPerson()方法，以确保 person 属性已设置。

package com.gp6.dependencyCheck.required;

import org.springframework.beans.factory.annotation.Required;

public class Customer {
    private Person person;
    
    private String action;
    
    private int type;


    public String getAction() {
        return action;
    }

    public void setAction(String action) {
        this.action = action;
    }

    public int getType() {
        return type;
    }

    public void setType(int type) {
        this.type = type;
    }

    public Person getPerson() {
        return person;
    }

    @Required
    public void setPerson(Person person) {
        this.person = person;
    }
}

简单地套用@Required注解不会强制执行该属性的检查，还需要注册一个RequiredAnnotationBeanPostProcessor以了解在bean配置文件@Required注解。

RequiredAnnotationBeanPostProcessor可以用两种方式来启用。

1. 包函 <context:annotation-config />

添加 Spring 上下文和 <context:annotation-config />在bean配置文件。

<beans 
    ...
    xmlns:context="http://www.springframework.org/schema/context"
    ...
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-2.5.xsd">
    ...
    <context:annotation-config />
    ...
</beans>

完整的实例,

<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-2.5.xsd
    http://www.springframework.org/schema/context
    http://www.springframework.org/schema/context/spring-context-2.5.xsd">

    <context:annotation-config />

    <bean id="CustomerBean" class="com.gp6.dependencyCheck.required.Customer">
        <property name="action" value="buy" />
        <property name="type" value="1" />
        <property name="person" ref="PersonBean" />
    </bean>

    <bean id="PersonBean" class="com.gp6.dependencyCheck.required.Person">
        <property name="name" value="gp6" />
        <property name="age" value="29" />
    </bean>
    
</beans>

2. 包函 RequiredAnnotationBeanPostProcessor

直接在 bean 配置文件包函“RequiredAnnotationBeanPostProcessor”。

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
    
<bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor"/>
    
    <bean id="CustomerBean" class="com.gp6.dependencyCheck.required.Customer">
        <property name="action" value="buy" />
        <property name="type" value="1" />
        <!-- <property name="person" ref="PersonBean" /> -->
    </bean>

    <bean id="PersonBean" class="com.gp6.dependencyCheck.required.Person">
        <property name="name" value="gp6" />
        <property name="age" value="29" />
    </bean>
    
</beans>

如果你运行它，下面的错误信息会丢的，因为 person 的属性未设置。

org.springframework.beans.factory.BeanInitializationException:  
    Property 'person' is required for bean 'CustomerBean'

结论

尝试@Required注解，它比依赖检查XML文件中更加灵活，因为它可以适用于只有一个特定属性。

Spring自定义@Required-style注解

@Required注解是用来确保特定属性已设置。如果您迁移现有项目到Spring框架或有自己的@Required-style注解，Spring允许您定义自定义@Required-style注解，相当于@Required注解。

在这个例子中，您将创建一个名为 @Mandatory 定制 @Required-style 注解，相当于@Required注解。

1.创建@MyRequired接口

package com.gp6.dependencyCheck.myRequired;

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.应用它到属性

package com.gp6.dependencyCheck.myRequired;

public class Customer {
    private Person person;
    
    private String action;
    
    private int type;


    public String getAction() {
        return action;
    }

    public void setAction(String action) {
        this.action = action;
    }

    public int getType() {
        return type;
    }

    public void setType(int type) {
        this.type = type;
    }

    public Person getPerson() {
        return person;
    }

    @MyRequired
    public void setPerson(Person person) {
        this.person = person;
    }
}

3.注册它

包函新@Mandatory注释到“RequiredAnnotationBeanPostProcessor' 类。

<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

    <bean class="org.springframework.beans.factory.annotation.RequiredAnnotationBeanPostProcessor">
        <property name="requiredAnnotationType" value="com.gp6.dependencyCheck.myRequired.MyRequired"/>
    </bean>
    
    <bean id="CustomerBean" class="com.gp6.dependencyCheck.myRequired.Customer">
        <property name="action" value="buy" />
        <property name="type" value="1" />
        <property name="person" ref="PersonBean" />
    </bean>
    
    <bean id="PersonBean" class="com.gp6.dependencyCheck.myRequired.Person">
        <property name="name" value="gp6" />
        <property name="age" value="29" />
    </bean>
    
</beans>

4. 完成

这样做，创建了一个新的自定义命名 @Required-style的@MyRequired 注解，相当于 @Required 注解