Question

I am attempting to autowire a WebApplicationContext into a class ImageCreatorUtil that I have created, within my Spring MVC project. Upon execution of a method in the class, which utilizes the application context, I always receive an NPE. It is important to note that this method is called by an ApplicationListener defined in another config file. I am not sure why the autowiring is not working. Can anyone provide any suggestions?

servlet-context.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.1.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-3.1.xsd">

    <!-- DispatcherServlet Context: defines this servlet's request-processing 
        infrastructure -->

    <!-- Enables the Spring MVC @Controller programming model -->
    <mvc:annotation-driven>
        <mvc:argument-resolvers>
            <bean class="org.springframework.data.web.PageableArgumentResolver" />
        </mvc:argument-resolvers>
    </mvc:annotation-driven>

    <!-- Intercept request to blog to add paging params -->
    <mvc:interceptors>
        <mvc:interceptor>
            <mvc:mapping path="/blog/**"/>
            <bean class="org.tothought.spring.interceptors.PageableRequestHandlerInterceptor" />
        </mvc:interceptor>
        <mvc:interceptor>
            <mvc:mapping path="/**"/>
            <bean class="org.tothought.spring.interceptors.LookupHandlerInterceptor" />
        </mvc:interceptor>
    </mvc:interceptors>

    <!-- Handles HTTP GET requests for /resources/** by efficiently serving 
        up static resources in the ${webappRoot}/resources directory -->
    <mvc:resources location="/resources/" mapping="/resources/**" />

    <!-- Resolves views selected for rendering by @Controllers to .jsp resources 
        in the /WEB-INF/views directory -->
    <bean
        class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/views/" />
        <property name="suffix" value=".jsp" />
    </bean>

    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <property name="maxUploadSize" value="5000000"/>
    </bean>

    <context:component-scan base-package="org.tothought.spring.**" />

</beans>

ImageCreatorUtil.java

@Component
public class ImageCreatorUtil {

    static Logger logger = LoggerFactory.getLogger(ImageCreatorUtil.class);
    static final String IMAGE_PATH_FRAGMENT = "/resources/images/resume/skills/uploaded-icons/";

    @Autowired
    private WebApplicationContext context;

    /**
     * Creates the provided file in the resources directory for access by the
     * web application.
     * 
     * @param appContext
     * @param image
     */
    public void storeImage(Image image) {
        if (image != null) {
            String realPath = ((WebApplicationContext)context).getServletContext().getRealPath("/");
            File tmpFile = new File(realPath + IMAGE_PATH_FRAGMENT + image.getName());

            try {
                logger.info("Saving image to :" + tmpFile.getAbsolutePath());
                FileUtils.writeByteArrayToFile(tmpFile, image.getFile());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

}

application-context.xml

<?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:jpa="http://www.springframework.org/schema/data/jpa"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/data/jpa http://www.springframework.org/schema/data/jpa/spring-jpa-1.1.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd">

    <context:property-placeholder location="classpath:META-INF/db/db.properties" />
    <context:annotation-config/>

    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
        destroy-method="close">
        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url" value="jdbc:mysql://localhost:3306/to_thought" />
        <property name="username" value="${db.user}" />
        <property name="password" value="${db.password}" />
    </bean>

    <bean id="entityManagerFactory"
        class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="persistenceUnitName" value="toThought" />
    </bean>

    <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
        <property name="entityManagerFactory" ref="entityManagerFactory" />
    </bean>

    <jpa:repositories base-package="org.tothought.repositories"/>

    <!-- Application Listeners -->
    <bean id="lookupLoader" class="org.tothought.spring.listeners.LookupLoaderApplicationListener" /> 
    <bean id="imageLoader" class="org.tothought.spring.listeners.ImageLoaderApplicationListener" /> 
</beans>

Console Error

SEVERE: Exception sending context initialized event to listener instance of class org.springframework.web.context.ContextLoaderListener
java.lang.NullPointerException
    at org.tothought.spring.utilities.ImageCreatorUtil.storeImage(ImageCreatorUtil.java:34)
    at org.tothought.spring.listeners.ImageLoaderApplicationListener.onApplicationEvent(ImageLoaderApplicationListener.java:29)
    at org.tothought.spring.listeners.ImageLoaderApplicationListener.onApplicationEvent(ImageLoaderApplicationListener.java:1)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:97)
    at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:324)

Answer 1

I have tried your code. The Autowiring for context works fines for context in any controller class but its not working when i am calling a method using object of a class. So if you do something like :

Your Controller :

@Autowired
private ImageCreatorUtil icu;

public String controllerMethod(....) {
    icu.storeImage();
}

Your application-context.xml :

<bean id="icu" class="****.controller.ImageCreatorUtil"/>

Then the Autowiring would work fine. I would try and update you the reason for such a behavior.