Null pointer exception while getting datasource from autowired bean

Question

I have just created a spring mvc project, there is nothing inside it except web.xml, spring-servlet.xml and ListnerClass.java.
I want to initialize system property during server startup. For this I created a servlet context

public class ListnerClass implements ServletContextListener{

    @Autowired
    private DataSource dataSource;

    @Override
    public void contextDestroyed(ServletContextEvent arg0) {

    }

    @Override
    public void contextInitialized(ServletContextEvent arg0) {

        /* code for initializing system properties */
    Connection conn=dataSource.getConnection();

}

I get NullPointerExceptin at this line Connection conn=dataSource.getConnection();

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    id="WebApp_ID" version="3.0">

    <servlet>
        <servlet-name>spring</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>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>
            /WEB-INF/spring-servlet.xml
        </param-value>
    </context-param>
    <listener>
        <listener-class>com.infocentercache.manager.ListnerClass</listener-class>
    </listener>

</webapp>

spring-servlet.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:context="http://www.springframework.org/schema/context"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xsi:schemaLocation="http://www.springframework.org/schema/mvc 
      http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
      http://www.springframework.org/schema/beans 
      http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
      http://www.springframework.org/schema/context 
      http://www.springframework.org/schema/context/spring-context-3.0.xsd">

<context:annotation-config/>

    <bean id="dataSource" class="org.apache.tomcat.jdbc.pool.DataSource">

        <property name="driverClassName" value="com.mysql.jdbc.Driver" />
        <property name="url"    value="jdbc:mysql://localhost:3306/infocenter" />
        <property name="username"   value="root" />
        <property name="password" value="gaurav" />
    </bean>
</beans>

Answer 1

A ServletContextListener object registered in a deployment descriptor is not managed by Spring, it is managed by the Servlet Container. As such, Spring has no business injecting any bean into it.

The rule of thumb is, if you have an @Autowired field target and it is null, Spring was not involved. Spring will throw all sorts of exceptions if it can't resolve the @Autowired target.

There are workarounds:

• Spring - Injecting a dependency into a ServletContextListener