Spring and null pointer exception

Question

I'm trying to do this:

@Controller    
public class HomeController {

        @Autowired
        private TemplatesService templatesService;    

        public final String TEST = templatesService.getUri();

The getUri:

@SuppressWarnings("unchecked")
    public String getUri() {

        return (String) sessionFactory.getCurrentSession()
                .createQuery("select uri from Templates WHERE state=1")
                .uniqueResult();
    }

It will work correctly, if I'll declare TEST in any method. But now I'm having this:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'homeController' defined in file [C:\Users\anton\springsource\vfabric-tc-server-developer-2.8.2.RELEASE\base-instance\wtpwebapps\blog\WEB-INF\classes\net\babobka\blog\controller\HomeController.class]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [net.babobka.blog.controller.HomeController]: Constructor threw exception; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:997)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:943)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:485)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:291)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:585)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:913)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:464)
    at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:385)
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:284)
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:111)

My root-context(I don't think it's helpful):

    <context:annotation-config />


    <context:component-scan base-package="net.babobka.blog" />
    <mvc:resources mapping="/resources/**" location="/resources/" />
    <cache:annotation-driven />

    <bean id="cacheManager" class="org.springframework.cache.support.SimpleCacheManager">
        <property name="caches">
            <set>
                <bean
                    class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean"
                    p:name="template" />
                <bean
                    class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean"
                    p:name="headHunter" />

            </set>
        </property>
    </bean>

    <bean id="converter" class="net.babobka.blog.headHunter.Converter" />


    <bean id="propertyConfigurer"
        class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"
        p:location="/WEB-INF/db/jdbc.properties" />

    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
        destroy-method="close" p:driverClassName="${jdbc.driverClassName}"
        p:url="${jdbc.databaseurl}" p:username="${jdbc.username}" p:password="${jdbc.password}" />
    <bean id="sessionFactory"
        class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="configLocation">
            <value>/WEB-INF/db/hibernate.cfg.xml</value>
        </property>
        <property name="configurationClass">
            <value>org.hibernate.cfg.AnnotationConfiguration</value>
        </property>
        <property name="hibernateProperties">
            <props>
                <prop key="hibernate.dialect">${jdbc.dialect}</prop>
                <prop key="hibernate.show_sql">${jdbc.show_sql}</prop>
                <prop key="hibernate.connection.useUnicode">true</prop>
                <prop key="hibernate.connection.characterEncoding">UTF-8</prop>
                <prop key="hibernate.connection.charSet">UTF-8</prop>
            </props>
        </property>
    </bean>




    <bean id="transactionManager"
        class="org.springframework.orm.hibernate3.HibernateTransactionManager">
        <property name="sessionFactory" ref="sessionFactory" />
    </bean>
    <mvc:annotation-driven />
    <tx:annotation-driven />
    <task:annotation-driven />



    <bean id="Backupper" class="net.babobka.blog.backupper.Backupper"></bean>

    <bean id="OldDataRemoval" class="net.babobka.blog.termination.OldDataRemoval"></bean>

    <bean id="HeadHunterImport" class="net.babobka.blog.headHunter.HeadHunterImport"></bean>

    <bean id="urlForwardController"
        class="org.springframework.web.servlet.mvc.UrlFilenameViewController" />

    <bean id="tilesConfigurer"
        class="org.springframework.web.servlet.view.tiles2.TilesConfigurer">
        <property name="definitions">
            <list>
                <value>/WEB-INF/tiles.xml</value>
            </list>
        </property>
    </bean>

    <bean id="viewResolver"
        class="org.springframework.web.servlet.view.UrlBasedViewResolver">
        <property name="viewClass"
            value="org.springframework.web.servlet.view.tiles2.TilesView" />
    </bean>





</beans>

What's wrong?

Provide spring configuration and also the annotated part of the controller class — Abhijith Nagarajan
– Abhijith Nagarajan, Commented Sep 24, 2013 at 16:29

Caesar Ralf · Accepted Answer · 2013-09-24 16:41:57Z

3

It's not working because templatesService is not yet injected when you reference it to set TEST. Fields injection will only work after the instantiation of your Object. What you need to solve this is use @PostConstruct to set test.

@Controller    
public class HomeController {

    @Autowired
    private TemplatesService templatesService;    

    public String test;

    @PostConstruct
    public void init() {
       this.test = templatesService.getUri();
    }

if you still want to use final, you can use injection by constructor and set TEST then.

  @Controller    
  public class HomeController {

    private TemplatesService templatesService;    

    public final String TEST;

    @Autowired
    public HomeController(TemplatesService templatesService) {
        this.templatesService = templatesService;
        this.TEST = templatesService.getUri();
    }

answered Sep 24, 2013 at 16:41

Caesar Ralf

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3 Comments

Tony Over a year ago

Seems nice. Could you tell me about PostConstruct in three words?

Caesar Ralf Over a year ago

@Tony PostConstruct is from JSR250. There's lot of material in the internet: docs.oracle.com/javaee/6/tutorial/doc/gmgkd.html

Caesar Ralf Over a year ago

@Tony basically is a way to declare that your bean have some computing to do after it's created. There's @PreDestroy for you to use when you need to something before destroying your bean. It's important to understand the lifecycle of creation/destruction of your beans. If you need anything else, just let me know.

meriton · Accepted Answer · 2013-09-24 16:38:40Z

This is a problem of initialization order. Spring will inject dependencies into @Autowired fields after it has invoked a bean's constructor, but a field initializer is executed during object construction - and therefore before the field has been autowired. The field is therefore still null, which is why attempting to invoke a method throws a NullPointerException.

Alternatives:

pass the TemplatesService by constructor injection, and assign the final field from the constructor rather than the field initializer
continue to inject the TemplatesService by field injection, but move initialization of the bean into a @PostConstruct method. You will have to remove final to pacify the compiler.
inject the TemplatesService by setter injection, and perform the necessary initialization in the setter. You will have to remove final to pacify the compiler.

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