Question

I am getting null pointer exception while trying to add anything in my solrQueue. I checked in debugger and it is because solrQueue is null. But I have autowired it in my application context then why this error?

public class Check {
    @Autowired
    public LinkedBlockingQueue<SolrInputDocument> solrQueue;
    public SolrInputDocument solrDoc;   
    public void solradd(){
        solrDoc=new SolrInputDocument();
        solrDoc.addField("title", "abc");
        solrQueue.add(solrDoc);//solrQueue is null 
    }
}

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:aop="http://www.springframework.org/schema/aop"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
        http://www.springframework.org/schema/aop 
        http://www.springframework.org/schema/aop/spring-aop-2.0.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-2.5.xsd">

    <context:annotation-config />
    <!--<context:component-scan base-package="com/abc" />   -->

    <bean id="solrQueue" class="java.util.concurrent.LinkedBlockingQueue" />
    <bean id="check" class="com.abc.Check" scope="prototype" />

</beans>

Answer 1

You are creating an instance of Check class manually rather than asking Spring to create/return one for you:

Check c=new Check();
c.solradd();

This will never* work since Spring has no knowledge about you created Check class. Depending on how do you start you Spring context, you must either explicitly ask the application context:

Check check = applicationContext.getBean(Check.class)

or inject the check bean into some other compoent like controller:

@Autowired
private Check check;

See also:

• Spring Dependency Injection Autowiring Null

^{* AspectJ weaving will do the trick, but this is like using a cannon to kill a fly}