Spring DI - Autowired property is null in a REST service

spring dependency-injection nullpointerexception jersey autowired
diegosasw picture diegosasw · Nov 2, 2013 · Viewed 23.3k times · Source

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 can help me out!

The problem is that a property annotated as @Autowired is always null

I've got a few projects with Maven structure:

  • com.diegotutor.lessondeliver
  • com.diegotutor.utility

I'm running the examples over Tomcat 7

I'm using the following dependencies in my pom.xml:

  • spring-context 3.2.4
  • spring-web 3.2.4
  • jersey-server 1.17.1
  • jersey-core 1.17.1
  • jersey-servlet 1.17.1

The simple idea is to have a RESTful service that through Dependency Injection is able to print out the value of a property located in a config file located at: D:\configuracion.conf.

At com.diegotutor.utility I have the following interface:

package com.diegotutor.utility;

public interface ConfigService {

    public String getProperty(final String propertyName);
}

Implemented by:

package com.diegotutor.utility.impl;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.util.Properties;

import com.diegotutor.utility.ConfigService;

public class PropertyFileConfigService implements ConfigService{

Properties prop;

public PropertyFileConfigService (final InputStream input) throws IOException {
    if(input == null) {
        throw new IllegalArgumentException("Input stream can't be null");
    }
    prop = new Properties();
    prop.load(input);
}

public PropertyFileConfigService (final String fileName) throws IOException {
    final FileInputStream input = new FileInputStream(fileName);
    prop = new Properties();
    prop.load(input);
}

public PropertyFileConfigService(final Reader input) throws IOException {
    prop = new Properties();
    prop.load(input);
}

public String getProperty(final String propertyName) {
    return prop.getProperty(propertyName);
}

}

And at com.diegotutor.lessondeliver I have the RESTful service where I would like to use an injected instance of the ConfigService:

package com.diegotutor.lessondeliver;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import com.diegotutor.utility.ConfigService;

@Path("/")
@Component
public class HelloWorld {

private static final Log log = LogFactory.getLog(HelloWorld.class);

@Autowired
private ConfigService configService;

@Path("/helloworld")
@GET
@Produces(MediaType.TEXT_PLAIN)
public String getHello() {
    String host = configService.getProperty("host");
    return "Hello World! HOST" + host;
            // configService IS NULL!! 
            //SO IT THROWS A NULLPOINTER EXCEPTION WHEN INVOKING getProperty ON IT
}
}

Finally at /com.diegotutor.lessondeliver/src/main/webapp/WEB-INF/service-beans.xml I have the following XML application context file, where I use the implementation of ConfigService (PropertyFileConfigService) injecting on it the path for the configuration file to read:

<?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.xsd
   http://www.springframework.org/schema/context
   http://www.springframework.org/schema/context/spring-context.xsd">

<bean id="configService" class="com.diegotutor.utility.impl.PropertyFileConfigService">
    <constructor-arg type="java.lang.String"
        value="D:\configuracion.conf" />
</bean>

<context:component-scan base-package="com.diegotutor" />

</beans>

Obviously I have specified in the web.xml of this com.diegotutor.lessondeliver web app that I want service-beans.xml as ConfigLocation and a listener ContextLoaderListener, and the RESTful service relies on ServletContainer

If I'm specifying context:component-scan to look for Components in com.diegotutor as suggested here and I'm forcing object creation through Spring by not using any new Statement as suggested here, Why am I getting the annotated configService as null? Why Spring is unable to inject an instance of com.diegotutor.utility.impl.PropertyFileConfigService?

Any help will be much appreciated!

Thank you

EDITED:

As requested, my web.xml is as follows:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xmlns="http://java.sun.com/xml/ns/javaee" 
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" 
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee     http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" 
id="WebApp_ID" version="3.0">

 <display-name>com.diegotutor.lessondeliver</display-name>

 <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/service-beans.xml</param-value>
 </context-param>

 <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
 </listener>

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

 <servlet-mapping>
  <servlet-name>jersey-servlet</servlet-name>
  <url-pattern>/rest/*</url-pattern>
 </servlet-mapping>
</web-app>

Answer

diegosasw picture diegosasw · Nov 3, 2013

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!

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