Null Pointer Exception while Autowiring LinkedBlockingQueue

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>

How do you obtain an instance of `Check` class? You are **not** calling `new Check()`, aren't you? — Tomasz Nurkiewicz, Jan 29 '12 at 14:57
I am calling this function throvy groovy class where I have included the following code — sparkle, Jan 29 '12 at 15:01
Can we do autowiring in groovy class because I tried it also and getting NPE in the autowired Check class in my groovy file.. — sparkle, Jan 29 '12 at 15:07

score 7 · Accepted Answer · edited May 23 '17 at 11:43

7

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;

Thanks for the reply.. but I didn't get u..I have explicitly included LinkedBlockingqueue bean..so I commented line..but I am also getting the similar error if I include the component scan line also.. :( – sparkle Jan 29 '12 at 14:49
@ŁukaszBachman: the `solrQueue` bean is defined in XML, no context scanning is needed. – Tomasz Nurkiewicz Jan 29 '12 at 14:56
yup..but how to remove null pointer exception..It is simple autowiring code – sparkle Jan 29 '12 at 14:58
@TomaszNurkiewicz, how in hell have I missed that? :D – ŁukaszBachman Jan 30 '12 at 07:22

score 0 · Answer 3 · answered Jan 29 '12 at 17:56

I don't think that you can mix annotation and XML based config. 2 solutions here :

Remove the declaration of the Check bean in your XML file and add a @Component annotation on your Check class.
Inject the solrQueue property to your bean in the XML :

<bean id="check" class="com.abc.Check" scope="prototype"> <property name="solrQueue" ref="solrQueue"/> </bean>

Null Pointer Exception while Autowiring LinkedBlockingQueue

3 Answers3

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