Spring DI - Autowired property is null in a REST service

Question

I\'m getting started with Spring DI, but I\'m struggling with dependency injection and the worse part is that I\'m not even sure why as it seems ok to me. Hopefully you guys

Answer 1

Integration Spring with Jersey 2 (org.glassfish.*):

Maven

Some dependencies may be unnecessary, please check & clear it after things got working.

    <properties>
        <jersey.version>2.5</jersey.version>
    </properties>

    <!-- Jersey -->
    <dependency>
        <groupId>org.glassfish.jersey.core</groupId>
        <artifactId>jersey-server</artifactId>
        <version>${jersey.version}</version>
    </dependency>

    <dependency>
        <groupId>org.glassfish.jersey.containers</groupId>
        <!-- if your container implements Servlet API older than 3.0, use "jersey-container-servlet-core" -->
        <artifactId>jersey-container-servlet</artifactId>
        <version>${jersey.version}</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.core</groupId>
        <artifactId>jersey-client</artifactId>
        <version>${jersey.version}</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.test-framework.providers</groupId>
        <artifactId>jersey-test-framework-provider-inmemory</artifactId>
        <version>${jersey.version}</version>
    </dependency>

    <!-- Jersey + Spring -->
    <dependency>
        <groupId>org.glassfish.jersey.ext</groupId>
        <artifactId>jersey-spring3</artifactId>
        <version>${jersey.version}</version>
        <exclusions>
            <exclusion>
                <groupId>org.springframework</groupId>
                <artifactId>spring</artifactId>
            </exclusion>
            <exclusion>
                <groupId>org.springframework</groupId>
                <artifactId>spring-core</artifactId>
            </exclusion>
            <exclusion>
                <groupId>org.springframework</groupId>
                <artifactId>spring-web</artifactId>
            </exclusion>
            <exclusion>
                <groupId>org.springframework</groupId>
                <artifactId>spring-beans</artifactId>
            </exclusion>
            <exclusion>
                <groupId>org.springframework</groupId>
                <artifactId>spring-context</artifactId>
            </exclusion>
        </exclusions>
    </dependency>

web.xml

<servlet>
    <servlet-name>my-rest-service</servlet-name>
    <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
    <init-param>
        <param-name>jersey.config.server.provider.packages</param-name>
        <param-value>my.package.with.rest.services</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>my-rest-service</servlet-name>
    <url-pattern>/api/*</url-pattern>
</servlet-mapping>

applicationContext.xml

During the Spring upgrading I had to move it from /main/webapp/WEB-INF/ to /main/resources/ (details).

<?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:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-2.5.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="my.package.with.rest.services" />
</beans>

Example REST service

public interface MyService
{
    String work(String s);
}

...

@Service
public class MyServiceImpl implements MyService
{
    @Override
    public String work(String s)
    {
        return "Hello, " + s;
    }
}

...

@Path("demo/")
@Component
public class DemoRestService
{
    @Autowired
    private MyService service;

    @GET
    @Path("test")
    public Response test(@FormParam("param") String par)
    {
        try
        {
            String entity = service.work(par);
            return Response.ok(entity).build();
        }
        catch (Exception e)
        {
            e.printStackTrace();
            return Response.status(Status.INTERNAL_SERVER_ERROR).entity("Epic REST Failure").build();
        }
    }
}

Answer 2

Another possible option is to manually invoke autowiring in your jersey resource:

@Context
private ServletContext servletContext;

@PostConstruct
public void init() {
    SpringBeanAutowiringSupport.processInjectionBasedOnServletContext(this, servletContext);
}

Hmm, you get a "manual autowiring"...

Answer 3

or you can simply extend SpringBeanAutoWiringSupport class. Like this: public class DemoRestService extends SpringBeanAutoWiringSupport. By extending this support class, properties of your service class can be auto-wired.

Answer 4

You were right! It seems that the problem is that Jersey is totally unaware of Spring and instantiates its own object. In order to make Jersey aware of Spring object creations (through dependency injection) I had to integrate Spring + Jersey.

To integrate:

1. Add maven dependencies

   <dependency>
       <groupId>com.sun.jersey.contribs</groupId>
       <artifactId>jersey-spring</artifactId>
       <version>1.17.1</version>
       <exclusions>
           <exclusion>
               <groupId>org.springframework</groupId>
               <artifactId>spring-core</artifactId>
           </exclusion>
           <exclusion>
               <groupId>org.springframework</groupId>
               <artifactId>spring-beans</artifactId>
           </exclusion>
           <exclusion>
               <groupId>org.springframework</groupId>
               <artifactId>spring-context</artifactId>
           </exclusion>
           <exclusion>
               <groupId>org.springframework</groupId>
               <artifactId>spring-web</artifactId>
           </exclusion>
       </exclusions>
   </dependency>
   

2. Use SpringServlet for jersey-servlet in web.xml

   <servlet>
       <servlet-name>jersey-servlet</servlet-name>
       <servlet-class>
           com.sun.jersey.spi.spring.container.servlet.SpringServlet
       </servlet-class>
       <load-on-startup>1</load-on-startup>
   </servlet>
   

Now the @Autowired works properly and the object is not null anymore.

I'm a little bit confused about the exclusions I have to use in maven when using jersey-spring dependency, but that's another issue :)

Thank you!