Welcome!

Java IoT Authors: Pat Romanski, Stackify Blog, Elizabeth White, Liz McMillan, Mamoon Yunus

Related Topics: Java IoT, Microservices Expo

Java IoT: Book Excerpt

Book Excerpt | Good Relationships: The Spring Data Neo4j Guide Book

Part 1: Tutorial - the creation of cineasts.net, a complete web application

The Spring Data Neo4j Project
This project is part of the Spring Data project, which brings the convenient programming model of the Spring Framework to modern NOSQL databases. Spring Data Neo4j, as the name alludes to, aims to provide support for the graph database Neo4j.

Tutorial
The first part of the book provides a tutorial that walks through the creation of a complete web application called cineasts.net, built with Spring Data Neo4j. Cineasts are people who love movies, and the site is a gathering place for moviegoers. For cineasts.net we decided to add a social aspect to the rating of movies, allowing friends to share their scores and get recommendations for new friends and movies.

The tutorial takes the reader through the steps necessary to create the application. It provides the configuration and code examples that are needed to understand what's happening in Spring Data Neo4j. The complete source code for the app is available on Github.

Introducing Our Project
Once upon a time we wanted to build a social movie database. At first there was only the name: Cineasts, the movie enthusiasts who have a burning passion for movies. So we went ahead and bought the domain cineasts.net, and so we were off to a good start.

We had some ideas about the domain model too. There would obviously be actors playing roles in movies. We also needed someone to rate the movies - enter the cineast. And cineasts, being the social people they are, they wanted to make friends with other fellow cineasts. Imagine instantly finding someone to watch a movie with, or share movie preferences with. Even better, finding new friends and movies based on what you and your friends like.

When we looked for possible sources of data, IMDB was our first stop. But they're a bit expensive for our taste, charging $15k USD for data access. Fortunately, we found themoviedb.org which provides user-generated data for free. They also have liberal terms and conditions, and a nice API for retrieving the data.

We had many more ideas, but we wanted to get something out there quickly. Here is how we envisioned the final website:

The Spring Stack
Being Spring developers, we naturally chose components from the Spring stack to do all the heavy lifting. After all, we have the concept etched out, so we're already halfway there.

What database would fit both the complex network of cineasts, movies, actors, roles, ratings, and friends, while also being able to support the recommendation algorithms that we had in mind? We had no idea.

But hold your horses, there is this new Spring Data project, started in 2010, that brings the convenience of the Spring programming model to NOSQL databases. That should be in line with what we already know, providing us with a quick start. We had a look at the list of projects supporting the different NOSQL databases out there. Only one of them mentioned the kind of social network we were thinking of - Spring Data Neo4j for the Neo4j graph database. Neo4j's slogan of "value in relationships" plus "Enterprise NOSQL" and the accompanying docs looked like what we needed. We decided to give it a try.

Required Setup
To set up the project we created a public Github account and began setting up the infrastructure for a Spring web project using Maven as the build system. We added the dependencies for the Spring Framework libraries, added the web.xml for the DispatcherServlet, and the applicationContext.xml in the webapp directory.

Example 2.1. Project pom.xml
<properties>
<spring.version>3.0.7.RELEASE</spring.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<!-- abbreviated for all the dependencies -->
<artifactId>spring-(core,context,aop,aspects,tx,webmvc)</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-test</artifactId>
<version>${spring.version}</version>
<scope>test</scope>
</dependency>
</dependencies>

Example 2.2. Project web.xml
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<servlet>
<servlet-name>dispatcherServlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>dispatcherServlet</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>

With this setup in place we were ready for the first spike: creating a simple MovieController showing a static view. See the Spring Framework documentation for information on doing this.

Example 2.3. applicationContext.xml
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd">
<context:annotation-config/>
<context:spring-configured/>
<context:component-scan base-package="org.neo4j.cineasts">
<context:exclude-filter type="annotation"
expression="org.springframework.stereotype.Controller"/>
</context:component-scan>
<tx:annotation-driven mode="proxy"/>
</beans>

Example 2.4. dispatcherServlet-servlet.xml
<mvc:annotation-driven/>
<mvc:resources mapping="/images/**" location="/images/"/>
<mvc:resources mapping="/resources/**" location="/resources/"/>
<context:component-scan base-package="org.neo4j.cineasts.controller"/>
<bean id="viewResolver"
class="org.springframework.web.servlet.view.InternalResourceViewResolver"
p:prefix="/WEB-INF/views/" p:suffix=".jsp"/>

We spun up Tomcat in STS with the App and it worked fine. For completeness we also added Jetty to the maven-config and tested it by invoking mvn jetty:run to see if there were any obvious issues with the config. It all seemed to work just fine.

Setting the Stage
We wanted to outline the domain model before diving into library details. We also looked at the data model of the themoviedb.org data to confirm that it matched our expectations. In Java code this looks pretty straightforward: The domain model:

Example 3.1. Domain model
class
Movie {
String id;
String title;
int
year;
Set<Role> cast;
}
class
Actor {
String id;
String name;
Set<Movie> filmography;
Role playedIn(Movie movie, String role) { ... }
}
class
Role {
Movie movie;
Actor actor;
String role;
}
class
User {
String login;
String name;
String password;
Set<Rating> ratings;
Set<User> friends;
Rating rate(Movie movie, int stars, String comment) { ... }
void
befriend(User user) { ... }
}
class
Rating {
User user;
Movie movie;
int
stars;
String comment;
}

Then we wrote some simple tests to show that the basic design of the domain is good enough so far. Just creating a movie, populating it with actors, and allowing users to rate it.

Learning Neo4j
Graphs Ahead

Now we needed to figure out how to store our chosen domain model in the chosen database. First we read up on graph databases, in particular our chosen one, Neo4j. The Neo4j data model consists of nodes and relationships, both of which can have key/value-style properties. What does that mean, exactly? Nodes are the graph database name for records, with property keys instead of column names.

That's normal enough. Relationships are the special part. In Neo4j, relationships are first-class citizens, meaning they are more than a simple foreign-key reference to another record; relationships carry information. So we can link together nodes into semantically rich networks. This really appealed to us. Then we found that we were also able to index nodes and relationships by {key, value} pairs. We also found that we could traverse relationships both imperatively using the core API and declaratively using a query-like Traversal Description. Besides those programmatic traversals there was the powerful graph query language called Cypher and an interesting looking DSL named Gremlin. So there was lots of ways of working with the graph.

We also learned that Neo4j is fully transactional and therefore upholds ACID guarantees for our data. Durability is actually a good thing and we didn't have to scale to trillions of users and movies yet.

This is unusual for NOSQL databases, but easier for us to get our head around than non-transactional eventual consistency. It also made us feel safe, though it also meant that we had to manage transactions. Something to keep in mind later.

We started out by doing some prototyping with the Neo4j core API to get a feeling for how it works. And also to see what the domain might look like when it's saved in the graph database. After adding the Maven dependency for Neo4j, we were ready to go.

Example 4.1. Neo4j Maven dependency
<dependency>
<groupId>org.neo4j</groupId>
<artifactId>neo4j</artifactId>
<version>1.6.M02</version>
</dependency>
Learning Neo4j

Example 4.2. Neo4j core API (transaction code omitted)
enum RelationshipTypes implements RelationshipType { ACTS_IN };
GraphDatabaseService gds = new EmbeddedGraphDatabase("/path/to/store");
Node forrest=gds.createNode();
forrest.setProperty("title","Forrest Gump");
forrest.setProperty("year",1994);
gds.index().forNodes("movies").add(forrest,"id",1);
Node tom=gds.createNode();
tom.setProperty("name","Tom Hanks");
Relationship role=tom.createRelationshipTo(forrest,ACTS_IN);
role.setProperty("role","Forrest");
Node movie=gds.index().forNodes("movies").get("id",1).getSingle();
assertEquals("Forrest Gump", movie.getProperty("title"));
for
(Relationship role : movie.getRelationships(ACTS_IN,INCOMING)) {
Node actor=role.getOtherNode(movie);
assertEquals("Tom Hanks", actor.getProperty("name"));
assertEquals("Forrest", role.getProperty("role"));
}

Spring Data Neo4j
Conjuring magic

So far it had all been pure Spring Framework and Neo4j. However, using the Neo4j code in our domain classes polluted them with graph database details. For this application, we wanted to keep the domain classes clean. Spring Data Neo4j promised to do the heavy lifting for us, so we continued investigating it.

Spring Data Neo4j comes with two mapping modes. The more powerful one depends heavily on AspectJ, so we ignored it for the time being. The simple direct POJO-mapping copies the data out of the graph and into our entities. Good enough for a web-application like ours.

The first step was to configure Maven:

Example 5.1. Spring Data Neo4j Maven configuration
<dependency>
<groupId>org.springframework.data</groupId>
<artifactId>spring-data-neo4j</artifactId>
<version>2.0.0.RELEASE</version>
</dependency>

The Spring context configuration was even easier, thanks to a provided namespace:

Example 5.2. Spring Data Neo4j context configuration
<beans xmlns="http://www.springframework.org/schema/beans" ...
xmlns:neo4j="http://www.springframework.org/schema/data/neo4j"
xsi:schemaLocation="... http://www.springframework.org/schema/data/neo4j
http://www.springframework.org/schema/data/neo4j/spring-neo4j-2.0.xsd">

...
<neo4j:config storeDirectory="data/graph.db"/>

...
</beans>

Annotating the Domain
Decorations

Looking at the Spring Data Neo4j documentation, we found a simple Hello World example and tried to understand it. We also spotted a compact reference card that helped us a lot. The entity classes were annotated with @NodeEntity. That was simple, so we added the annotation to our domain classes too.

Entity classes representing relationships were instead annotated with @RelationshipEntity. Property fields were taken care of automatically. The only additional field we had to provide for all entities was an id-field to store the node- and relationship-ids.

Example 6.1. Movie class with annotation
@NodeEntity
class
Movie {
@GraphId Long nodeId;
String id;
String title;
int
year;
Set<Role> cast;
}

It was time to put our entities to the test. How could we now be assured that an attribute really was persisted to the graph store? We wanted to load the entity and check the attribute. Either we could have a Neo4jTemplate injected and use its findOne(id,type) method to load the entity. Or use a more versatile Repository. The same goes for persisting entities, both Neo4jTemplate or the Repository could be used. We decided to keep things simple for now. Here's what our test ended up looking like:

Example 6.2. First test case
@Autowired Neo4jTemplate template;
@Test @Transactional public void persistedMovieShouldBeRetrievableFromGraphDb() {
Movie forrestGump = template.save(new Movie("Forrest Gump", 1994));
Movie retrievedMovie = template.findOne(forrestGump.getNodeId(), Movie.class);
assertEqual("retrieved movie matches persisted one", forrestGump, retrievedMovie);
assertEqual("retrieved movie title matches", "Forrest Gump", retrievedMovie.getTitle());
}

As Neo4j is transactional, we have to provide the transactional boundaries for mutating operations.

Indexing
Do I Know You?

There is an @Indexed annotation for fields. We wanted to try this out, and use it to guide the next test. We added @Indexed to the id field of the Movie class. This field is intended to represent the external ID that will be used in URIs and will be stable across database imports and updates. This time we went with a simple GraphRepository to retrieve the indexed movie.

Example 7.1. Exact Indexing for Movie id
@NodeEntity class Movie {
@Indexed String id;
String title;
int
year;
}
@Autowired Neo4jTemplate template;
@Test @Transactional
public void
persistedMovieShouldBeRetrievableFromGraphDb() {
int
id = 1;
Movie forrestGump = template.save(new Movie(id, "Forrest Gump", 1994));
GraphRepository<Movie> movieRepository =
template.repositoryFor(Movie.class);
Movie retrievedMovie = movieRepository.findByPropertyValue("id", id);
assertEqual("retrieved movie matches persisted one", forrestGump, retrievedMovie);
assertEqual("retrieved movie title matches", "Forrest Gump", retrievedMovie.getTitle());
}

Repositories
Serving a Good Cause

We wanted to add repositories with domain-specific operations. Interestingly there was support for a very advanced repository infrastructure. Just declare an entity-specific repository interface and get all commonly used methods for free without implementing any of the boilerplate code. We started by creating a movie-related repository, simply by creating an empty interface.

Example 8.1. Movie repository
package
org.neo4j.cineasts.repository;
public interface
MovieRepository extends GraphRepository<Movie> {}

Then we enabled repository support in the Spring context configuration by simply adding:

Example 8.2. Repository context configuration
<neo4j:repositories base-package="org.neo4j.cineasts.repository"/>

Besides the existing repository operations (like CRUD, and many standard queries) it was possible to declare custom methods, which we explored later. Those methods' names could be more domain-centric and expressive than the generic operations. For simple use-cases like finding by ids this is good enough. We first let Spring autowire our MovieController with the MovieRepository. That way we could perform simple persistence operations.

Example 8.3. Usage of a repository
@Autowired MovieRepository repo;

...
Movie movie = repo.findByPropertyValue("id",movieId);

We went on exploring the repository infrastructure. A very cool feature was something that we so far only heard about from Grails developers. Deriving queries from method names. Impressive! We had a more explicit method for the id lookup.

Example 8.4. Derived movie-repository query method
public interface
MovieRepository extends GraphRepository<Movie> {
Movie getMovieById(String id);
}

In our wildest dreams we imagined the method names we would come up with, and what kinds of queries those could generate. But some more complex queries would be cumbersome to read and write. In those cases it is better to just annotate the finder method. We did this much later, and just wanted to give you a peek into the future. There is much more, you can do with repositories; it is worthwhile to explore.

Example 8.5. Annotated movie-repository query method
public interface
MovieRepository extends GraphRepository<Movie> {
@Query("start user=node:User({0}) match user-[r:RATED]->movie return movie order by r.stars desc limit Iterable<Movie> getTopRatedMovies(User uer);
}

•   •   •

Republished from the Good Relationships: The Spring Data Neo4j Guide Book.

More Stories By Mike Hunger

Mike Hunger has been passionate about software development for a long time. He is particularly interested in the people who develop software, software craftsmanship, programming languages, and improving code. For the last two years he has been working with Neo Technology on the Neo4j graph database. As the project lead of Spring Data Neo4j he helped developing the idea to become a convenient and complete solution for object graph mapping. He is also taking care of Neo4j cloud hosting efforts.

As a developer he loves to work with many aspects of programming languages, learning new things every day, participating in exciting and ambitious open source projects and contributing to different programming related books. Michael is also an active editor and interviewer at InfoQ.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
Internet-of-Things discussions can end up either going down the consumer gadget rabbit hole or focused on the sort of data logging that industrial manufacturers have been doing forever. However, in fact, companies today are already using IoT data both to optimize their operational technology and to improve the experience of customer interactions in novel ways. In his session at @ThingsExpo, Gordon Haff, Red Hat Technology Evangelist, shared examples from a wide range of industries – including en...
Detecting internal user threats in the Big Data eco-system is challenging and cumbersome. Many organizations monitor internal usage of the Big Data eco-system using a set of alerts. This is not a scalable process given the increase in the number of alerts with the accelerating growth in data volume and user base. Organizations are increasingly leveraging machine learning to monitor only those data elements that are sensitive and critical, autonomously establish monitoring policies, and to detect...
"We're a cybersecurity firm that specializes in engineering security solutions both at the software and hardware level. Security cannot be an after-the-fact afterthought, which is what it's become," stated Richard Blech, Chief Executive Officer at Secure Channels, in this SYS-CON.tv interview at @ThingsExpo, held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA.
To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. Jack Norris reviews best practices to show how companies develop, deploy, and dynamically update these applications and how this data-first...
Intelligent Automation is now one of the key business imperatives for CIOs and CISOs impacting all areas of business today. In his session at 21st Cloud Expo, Brian Boeggeman, VP Alliances & Partnerships at Ayehu, will talk about how business value is created and delivered through intelligent automation to today’s enterprises. The open ecosystem platform approach toward Intelligent Automation that Ayehu delivers to the market is core to enabling the creation of the self-driving enterprise.
The question before companies today is not whether to become intelligent, it’s a question of how and how fast. The key is to adopt and deploy an intelligent application strategy while simultaneously preparing to scale that intelligence. In her session at 21st Cloud Expo, Sangeeta Chakraborty, Chief Customer Officer at Ayasdi, will provide a tactical framework to become a truly intelligent enterprise, including how to identify the right applications for AI, how to build a Center of Excellence to ...
SYS-CON Events announced today that Massive Networks will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Massive Networks mission is simple. To help your business operate seamlessly with fast, reliable, and secure internet and network solutions. Improve your customer's experience with outstanding connections to your cloud.
Everything run by electricity will eventually be connected to the Internet. Get ahead of the Internet of Things revolution and join Akvelon expert and IoT industry leader, Sergey Grebnov, in his session at @ThingsExpo, for an educational dive into the world of managing your home, workplace and all the devices they contain with the power of machine-based AI and intelligent Bot services for a completely streamlined experience.
Because IoT devices are deployed in mission-critical environments more than ever before, it’s increasingly imperative they be truly smart. IoT sensors simply stockpiling data isn’t useful. IoT must be artificially and naturally intelligent in order to provide more value In his session at @ThingsExpo, John Crupi, Vice President and Engineering System Architect at Greenwave Systems, will discuss how IoT artificial intelligence (AI) can be carried out via edge analytics and machine learning techn...
SYS-CON Events announced today that Datera, that offers a radically new data management architecture, has been named "Exhibitor" of SYS-CON's 21st International Cloud Expo ®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Datera is transforming the traditional datacenter model through modern cloud simplicity. The technology industry is at another major inflection point. The rise of mobile, the Internet of Things, data storage and Big...
Consumers increasingly expect their electronic "things" to be connected to smart phones, tablets and the Internet. When that thing happens to be a medical device, the risks and benefits of connectivity must be carefully weighed. Once the decision is made that connecting the device is beneficial, medical device manufacturers must design their products to maintain patient safety and prevent compromised personal health information in the face of cybersecurity threats. In his session at @ThingsExpo...
In his session at @ThingsExpo, Arvind Radhakrishnen discussed how IoT offers new business models in banking and financial services organizations with the capability to revolutionize products, payments, channels, business processes and asset management built on strong architectural foundation. The following topics were covered: How IoT stands to impact various business parameters including customer experience, cost and risk management within BFS organizations.
SYS-CON Events announced today that CA Technologies has been named "Platinum Sponsor" of SYS-CON's 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. CA Technologies helps customers succeed in a future where every business - from apparel to energy - is being rewritten by software. From planning to development to management to security, CA creates software that fuels transformation for companies in the applic...
From 2013, NTT Communications has been providing cPaaS service, SkyWay. Its customer’s expectations for leveraging WebRTC technology are not only typical real-time communication use cases such as Web conference, remote education, but also IoT use cases such as remote camera monitoring, smart-glass, and robotic. Because of this, NTT Communications has numerous IoT business use-cases that its customers are developing on top of PaaS. WebRTC will lead IoT businesses to be more innovative and address...
An increasing number of companies are creating products that combine data with analytical capabilities. Running interactive queries on Big Data requires complex architectures to store and query data effectively, typically involving data streams, an choosing efficient file format/database and multiple independent systems that are tied together through custom-engineered pipelines. In his session at @BigDataExpo at @ThingsExpo, Tomer Levi, a senior software engineer at Intel’s Advanced Analytics ...
SYS-CON Events announced today that App2Cloud will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct. 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. App2Cloud is an online Platform, specializing in migrating legacy applications to any Cloud Providers (AWS, Azure, Google Cloud).
Recently, IoT seems emerging as a solution vehicle for data analytics on real-world scenarios from setting a room temperature setting to predicting a component failure of an aircraft. Compared with developing an application or deploying a cloud service, is an IoT solution unique? If so, how? How does a typical IoT solution architecture consist? And what are the essential components and how are they relevant to each other? How does the security play out? What are the best practices in formulating...
SYS-CON Events announced today that MobiDev, a client-oriented software development company, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MobiDev is a software company that develops and delivers turn-key mobile apps, websites, web services, and complex software systems for startups and enterprises. Since 2009 it has grown from a small group of passionate engineers and business...
Internet of @ThingsExpo, taking place October 31 - November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 21st Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devic...
SYS-CON Events announced today that Dasher Technologies will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Dasher Technologies, Inc. ® is a premier IT solution provider that delivers expert technical resources along with trusted account executives to architect and deliver complete IT solutions and services to help our clients execute their goals, plans and objectives. Since 1999, we'v...