Spring beans created but not autowired

Question

I know there are so many similar questions about this. I looked through a lot of them but the problem still remains.

I have a service that gets created but is not autowired. There is no(!) manual initiation, neither in the project nor in tests (like in this question)

Both beans are found and created, says Tomcat output. At least the first service is not injected where it should be. I don't know about the second one.

Service (Interface):

public interface SchoolService {
  public School getSchool(String id);
}

Service (Implementation):

@Service
@Transactional
public class SchoolServiceImpl implements SchoolService {

  @Autowired
  private SchoolDAO schoolDAO;

  public School getSchool(String id) {
    //database things
    return school;
  }

}

Where it gets "called"

public class SchoolMenu implements Serializable {

  @Autowired
  private SchoolService schoolService;

  public SchoolMenu () {
    //here schoolService is null
    School school = schoolService.getSchool("id");
  }

}

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:p="http://www.springframework.org/schema/p"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
       http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd
       http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd">


    <bean id="SchoolServiceImpl" class="content_management.School.service.SchoolServiceImpl"/>
    <bean id="SchoolDAOImpl" class="content_management.School.dao.SchoolDAOImpl"/>
</beans>

Tomcat Output:

org.springframework.beans.factory.support.DefaultListableBeanFactory: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@57003970: defining beans [SchoolServiceImpl,SchoolDAOImpl]; root of factory hierarchy
org.springframework.beans.factory.support.DefaultListableBeanFactory: Creating shared instance of singleton bean 'SchoolServiceImpl'
org.springframework.beans.factory.support.DefaultListableBeanFactory: Creating instance of bean 'SchoolServiceImpl'
org.springframework.beans.factory.support.DefaultListableBeanFactory: Eagerly caching bean 'SchoolServiceImpl' to allow for resolving potential circular references
org.springframework.beans.factory.support.DefaultListableBeanFactory: Finished creating instance of bean 'SchoolServiceImpl'
org.springframework.beans.factory.support.DefaultListableBeanFactory: Creating shared instance of singleton bean 'SchoolDAOImpl'
org.springframework.beans.factory.support.DefaultListableBeanFactory: Creating instance of bean 'SchoolDAOImpl'
org.springframework.beans.factory.support.DefaultListableBeanFactory: Eagerly caching bean 'SchoolDAOImpl' to allow for resolving potential circular references
org.springframework.beans.factory.support.DefaultListableBeanFactory: Finished creating instance of bean 'SchoolDAOImpl'

Where is my error?

You're attempting to use the field from the constructor, before Spring has had a chance to do anything. — chrylis -cautiouslyoptimistic-, Apr 22 '15 at 13:50

score 2 · Answer 1 · answered Apr 22 '15 at 13:35

In order for @Autowired to work, SchoolMenu also has to be a Spring bean. If it is not, you can get schoolService from application context. Something like this

ApplicationContext appContext = new ClassPathXmlApplicationContext("application-context.xml");
SchoolService schoolService = (SchoolService) appContext.getBean(SchoolService.class);

score 2 · Answer 2 · answered Apr 22 '15 at 13:41

2

You're accessing schoolService in the constructor of SchoolMenu:

public SchoolMenu () {
    //here schoolService is null
    School school = schoolService.getSchool("id");
}

At that point, schoolService is not yet injected. It couldn't be - nothing can happen before the constructor has been invoked.

You can declare a method to be invoked after the bean is initialized, by annotating it with the javax.annotation.PostConstruct annotation. Perform actions that need the injected dependencies in that method, not in the constructor.

(There are a few other ways to achieve the same, such as implementing the InitializingBean interface, but these are a bit outdated)

Example:

public SchoolMenu () {
}

@PostConstruct
public void init() {
    // schoolService is NOT null here
    School school = schoolService.getSchool("id");
}

answered Apr 22 '15 at 13:41

Erwin Bolwidt

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1

Even more preferable is to use constructor injection in the first place. – chrylis -cautiouslyoptimistic- Apr 22 '15 at 13:51
Constructor injection has many advantages, but one big disadvantage: it can't resolve cycles in dependencies (two services referring to each other using constructor injection cannot be initialized - at least one of them needs setter or field injection) – Erwin Bolwidt Apr 22 '15 at 13:55
1

Yes, but (1) that's not the case here as far as I can tell and (2) cyclic dependencies are nearly always a sign of a design problem. – chrylis -cautiouslyoptimistic- Apr 22 '15 at 14:04
Citation for (2)? I have never encountered a situation in which constructor injection provides a dependency that isn't "constructed" per CDI. – chrylis -cautiouslyoptimistic- Apr 23 '15 at 02:28
You're right about initialization, constructor arguments are fully initialized. I guess that's why you get cyclic dependency errors more often than you would expect if this wasn't a requirement. – Erwin Bolwidt Apr 23 '15 at 02:45

Tony Vu · Answer 3 · 2015-04-23T07:02:50.947

Instead of defining beans in xml, you can use component scan by adding this config to your application-context and Spring will scan and detect the bean automatically for you.

<context:component-scan base-package="content_management.School" />

Also you need to add in the context namespace so the application-context.xml will look like this:

<?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:p="http://www.springframework.org/schema/p"
   xmlns:aop="http://www.springframework.org/schema/aop"
   xmlns:tx="http://www.springframework.org/schema/tx"
   xmlns:context="http://www.springframework.org/schema/context"
   xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
   http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.0.xsd
   http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-4.0.xsd
    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

 <context:component-scan base-package="content_management.School" />

 </beans>

I added both namespace and scan snippet, but I get `XmlBeanDefinitionStoreException: Line 26 in XML document from ServletContext resource [/WEB-INF/applicationContext.xml] is invalid; nested exception is org.xml.sax.SAXParseException; lineNumber: 26; columnNumber: 78; cvc-complex-type.2.4.c: ` — sebastian, Apr 22 '15 at 15:02
Can you show line 26 of your applicationContext.xml or even better the whole file? Seems like syntax error — Tony Vu, Apr 23 '15 at 01:28
Sorry I miss out the schemaLocation for context. I have updated my answer. Also verify that the base-package is correct. It must point to the package which contains both your SchoolDAO and SchoolService. — Tony Vu, Apr 23 '15 at 07:05

Spring beans created but not autowired

3 Answers3