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. :)