How to @Autowire objects in Validator classes?

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有刺的猬
有刺的猬 2021-02-14 06:36

Is it possible to Autowire an object in a Validation class? I keep getting null for the object that is supposed to be Autowired...

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  • 2021-02-14 06:46

    Are your Validation class an enabled Spring bean ??? If not, you always will get null for your object autowired. Make sure you have enabled your Validation class.

    And do not forget enable The Annotation config bean post-processor (see <context:annotation-config /> element)

    <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 />
    </beans>
    

    How to enable your Validation class as a managed Spring bean. Either

    By using xml (As shown above)

    <beans ...>
        <bean class="AccessRequestValidator"/>
        <context:annotation-config />
    </beans>
    

    By using annotation instead (Notice @Component just above class)

    @Component
    public class AccessRequestValidator implements Validator {
    
    }
    

    But to enable Spring annotated component scanning, you must enable a bean-post processor (notice <context:component-scan element)

    <beans ...>
        <context:annotation-config />
        <context:component-scan base-package="<PUT_RIGHT_HERE_WHICH_ROOT_PACKAGE_SHOULD_SPRING_LOOK_FOR_ANY_ANNOTATED_BEAN>"/>
    </beans>
    

    Inside your Controller, just do it (Do not use new operator)

    Choose one of the following strategies

    public class MyController implements Controller {
    
        /**
          * You can use FIELD @Autowired
          */
        @Autowired
        private AccessRequestValidator accessRequestValidator;
    
        /**
          * You can use PROPERTY @Autowired
          */
        private AccessRequestValidator accessRequestValidator;
        private @Autowired void setAccessRequestValidator(AccessRequestValidator accessRequestValidator) {
            this.accessRequestValidator = accessRequestValidator;
        }
    
        /**
          * You can use CONSTRUCTOR @Autowired
          */
        private AccessRequestValidator accessRequestValidator;
    
        @Autowired
        public MyController(AccessRequestValidator accessRequestValidator) {
            this.accessRequestValidator = accessRequestValidator;
        }   
    
    }
    

    UPDATE

    Your web app structure should looks like

    <CONTEXT-NAME>/
           WEB-INF/
               web.xml
               <SPRING-SERVLET-NAME>-servlet.xml
               business-context.xml
               classes/
                   /com
                       /wuntee
                           /taac
                               /validator
                                   AccessRequestValidator.class
               lib/
                   /**
                     * libraries needed by your project goes here
                     */
    

    Your web.xml should looks like (NOTICE contextConfigLocation context-param and ContextLoaderListener)

    <web-app version="2.4" 
        xmlns="http://java.sun.com/xml/ns/j2ee" 
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
                           http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
        <context-param>
            <param-name>contextConfigLocation</param-name>
            <!--If your business-context.xml lives in the root of classpath-->
            <!--replace by classpath:business-context.xml-->
            <param-value>
                /WEB-INF/business-context.xml
            </param-value>
        </context-param>
        <listener>
            <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
        </listener>
        <servlet>
            <servlet-name><SPRING-SERVLET-NAME></servlet-name>
            <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
            <load-on-startup>1</load-on-startup>
        </servlet>
        <servlet-mapping>
            <servlet-name><SPRING-SERVLET-NAME></servlet-name>
            <url-pattern>*.htm</url-pattern>
        </servlet-mapping>
    </web-app>
    

    Your <SPRING-SERVLET-NAME>-servlet.xml should looks like (Notice i am using Spring 2.5 - replace if you are using 3.0)

     <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">
        <!--ANY HANDLER MAPPING-->
        <!--ANY VIEW RESOLVER-->
        <context:component-scan base-package="com.wuntee.taac"/>
        <context:annotation-config/>
    </beans>
    
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  • 2021-02-14 06:53

    Trying to follow what you show above, I am still getting a null pointer:

    context.xml:

    <context:annotation-config />
    <context:component-scan base-package="com.wuntee.taac"/>
    

    AccessRequestValidator.java

    package com.wuntee.taac.validator;
    
    @Component
    public class AccessRequestValidator implements Validator {
    
        @Autowired
        private UserAccessCache userAccessCache;
    ...
    }
    

    business-context.xml:

       <bean id="userAccessCache" class="com.wuntee.taac.controller.UserAccessCache">
            <property name="cadaDao" ref="cadaDao" />
            <property name="adDao" ref="adDao" />
       </bean>
    

    Does the scanner recursively scan the tree?

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