Spring and null pointer exception - spring

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?

Answer 1

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();
}

Answer 2

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.