Graphs in the Cloud: Spring + Neo4j on Heroku

Last week I hosted a webinar about running Java apps on Heroku that use the Spring Framework and the Neo4j graph database. Here is the recording of that webinar:

In the webinar I began by deploying a copy of the Spring MVC + Hibernate template app from heroku.com/java on Heroku. Then I made a few modifications to the app to switch the persistence from Hibernate / JPA to Neo4j. You can get the full source code on GitHub.

Here is a quick recap of what I did to switch the template app to use Neo4j:

  1. Added the Neo4j Heroku Add-on:
    heroku addons:add neo4j
  2. Added the Spring Data Neo4j dependencies (optionally you can remove the unused JPA dependencies) to the “pom.xml” Maven build descriptor:
    <dependency>
        <groupId>org.springframework.data</groupId>
        <artifactId>spring-data-neo4j-rest</artifactId>
        <version>2.0.1.RELEASE</version>
    </dependency>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-validator</artifactId>
        <version>4.2.0.Final</version>
    </dependency>
  3. Modified the “src/main/java/com/example/service/PersonService.java” interface to use the Neo4j GraphRepository:
    package com.example.service;
     
    import com.example.model.Person;
    import org.springframework.data.neo4j.repository.GraphRepository;
     
    public interface PersonService extends GraphRepository<Person> {
     
     
    }
  4. Removed the unneeded “src/main/java/com/example/service/PersonServiceImpl.java” DAO.
  5. Modified the “src/main/java/com/example/model/Person.java” POJO to be a @NodeEntity (instead of JPA Entity) and switched the “id” primary key property to be a Long annotated as a @GraphId:
    package com.example.model;
     
    import org.springframework.data.neo4j.annotation.GraphId;
    import org.springframework.data.neo4j.annotation.NodeEntity;
     
    @NodeEntity
    public class Person {
     
        @GraphId
        private Long id;
     
        // the rest is omitted
  6. Modified the “src/main/java/com/example/controller/PersonController.java” Spring MVC controller to use the new “PersonService”, take a Long parameter in the “deletePerson” method, and make the “deletePerson” and “addPerson” methods transactional:
    package com.example.controller;
     
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Controller;
    import org.springframework.transaction.annotation.Transactional;
    import org.springframework.web.bind.annotation.ModelAttribute;
    import org.springframework.web.bind.annotation.PathVariable;
    import org.springframework.web.bind.annotation.RequestMapping;
    import org.springframework.web.bind.annotation.RequestMethod;
     
    import com.example.model.Person;
    import com.example.service.PersonService;
     
    import java.util.Map;
     
    @Controller
    public class PersonController {
     
        @Autowired
        private PersonService personService;
     
        @RequestMapping("/")
        public String listPeople(Map<String, Object> map) {
            map.put("person", new Person());
            map.put("peopleList", personService.findAll().iterator());
            return "people";
        }
     
        @RequestMapping(value = "/add", method = RequestMethod.POST)
        @Transactional
        public String addPerson(@ModelAttribute("person") Person person) {
            personService.save(person);
            return "redirect:/people/";
        }
     
        @RequestMapping("/delete/{personId}")
        @Transactional
        public String deletePerson(@PathVariable("personId") Long personId) {
            personService.delete(personId);
            return "redirect:/people/";
        }
    }
  7. Then I modified the “src/main/resources/applicationContext.xml” Spring config file to use a file for local Neo4j storage in the “default” profile and then in the “prod” profile the “NEO4J_REST_URL”, “NEO4J_LOGIN”, and “NEO4J_PASSWORD” environment variables are used to connect to the Neo4j Heroku add-on service:
    <?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"
           xmlns:tx="http://www.springframework.org/schema/tx"
           xmlns:mvc="http://www.springframework.org/schema/mvc"
           xmlns:neo4j="http://www.springframework.org/schema/data/neo4j"
           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
                               http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd
                               http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
                               http://www.springframework.org/schema/data/neo4j http://www.springframework.org/schema/data/neo4j/spring-neo4j-2.0.xsd">
     
        <context:annotation-config />
        <context:spring-configured />
        <context:component-scan base-package="com.example" />
     
        <neo4j:repositories base-package="com.example.service"/>
     
        <mvc:annotation-driven/>
     
        <bean id="jspViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
            <property name="viewClass" value="org.springframework.web.servlet.view.JstlView" />
            <property name="prefix" value="/WEB-INF/jsp/" />
            <property name="suffix" value=".jsp" />
        </bean>
     
        <tx:annotation-driven />
     
        <beans profile="default">
            <neo4j:config storeDirectory="target/neo4j-db"/>
        </beans>
     
        <beans profile="prod">
            <bean class="org.springframework.data.neo4j.rest.SpringRestGraphDatabase" id="graphDatabaseService">
                <constructor-arg index="0" value="#{systemEnvironment['NEO4J_REST_URL']}"/>
                <constructor-arg index="1" value="#{systemEnvironment['NEO4J_LOGIN']}"/>
                <constructor-arg index="2" value="#{systemEnvironment['NEO4J_PASSWORD']}"/>
            </bean>
     
            <neo4j:config graphDatabaseService="graphDatabaseService"/>
        </beans>
     
    </beans>
  8. After testing my changes locally (which actually didn’t work in my webinar due to a problem with Eclipse) I committed my changes to the git repo and pushed them to Heroku:
    git push heroku master

If you want to just skip to a working example on the cloud, simply follow the instructions in the project README.

Hopefully that helps you get started with Neo4j and Java applications on the cloud!

BTW: If you watched the webinar, you probably noticed that my Maven and Eclipse were misbehaving. Turns out that M2E didn’t read my Maven config and all I had to do was right-click on the project, select Maven, and then Update Project Configuration. That got everything back in sync. My excuse for not being able to figure that out during the demo… I usually use IntelliJ IDEA. :)

This entry was posted in Heroku, Neo4j, Spring. Bookmark the permalink. Post a comment or leave a trackback: Trackback URL.
  • Saraandreson8

    I apply all the instruction of what  you did to switch the template app to use N .Its great and i  got all my expectations.Thanks for sharing.

  • Jon

    Hello James, Thx for the tutorial…

    I’ve been following all these steps, but I’m always getting the exception:

    org.springframework.beans.factory.BeanCreationException: Error creating bean with name ‘personController’: Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private com.example.service.PersonService com.example.controller.PersonController.personService; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name ‘personService’: Cannot resolve reference to bean ‘neo4jTemplate’ while setting bean property ‘neo4jTemplate’; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name ‘org.springframework.data.neo4j.config.Neo4jConfiguration#0′: Cannot resolve reference to bean ‘graphDatabaseService’ while setting bean property ‘graphDatabaseService’; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name ‘graphDatabaseService’ defined in class path resource [applicationContext.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Could not instantiate bean class [org.springframework.data.neo4j.rest.SpringRestGraphDatabase]: Constructor threw exception; nested exception is java.lang.NullPointerException

    I’ve also tried the GitHub tutorial at https://github.com/jamesward/hello-java-spring-neo4j/blob/master/README.md. However I have the same issue.

    Any ideia what is going on?

    • jon

      Actually I’ve realized I have only ‘NEO4J_URL’ Environment Variables in my list after I perform ‘heroku config’. Is there some kind of trick to obtain NEO4J_REST_URL, NEO4J_LOGIN and NEO4J_PASSWORD or these should be available automatically ? Thank you.

    • http://www.jamesward.com James Ward

      Something is getting a null and it shouldn’t be. Perhaps this is something coming from the configuration?



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