Accessing Neo4j Data with REST :: Learn how to work with RESTful, hypermedia-based data persistence using Spring Data REST.
Shell Batchfile Java
Latest commit 83da25a Dec 24, 2016 @gregturn gregturn Add neo4j to CI testing

README.adoc

tags projects
spring-data
neo4j
rest
hateoas
spring-data-rest

This guide walks you through the process of creating an application that accesses graph-based data through a hypermedia-based RESTful front end.

What you’ll build

You’ll build a Spring application that let’s you create and retrieve Person objects stored in a Neo4j NoSQL database using Spring Data REST. Spring Data REST takes the features of Spring HATEOAS and Spring Data Neo4j and combines them together automatically.

Note
Spring Data REST also supports Spring Data JPA, Spring Data Gemfire and Spring Data MongoDB as backend data stores, but those are not part of this guide.

Standing up a Neo4j server

Before you can build a this application, you need to set up a Neo4j server.

Neo4j has an open source server you can install for free:

On a Mac, just type:

$ brew install neo4j

Once you installed, launch it with it’s default settings:

$ neo4j start

You should see a message like this:

Starting Neo4j.
Started neo4j (pid 96416). By default, it is available at http://localhost:7474/
There may be a short delay until the server is ready.
See /usr/local/Cellar/neo4j/3.0.6/libexec/logs/neo4j.log for current status.

By default, Neo4j has a username/password of neo4j/neo4j. However, it requires that the new account password be changed. To do so, execute the following command:

$ curl -v -u neo4j:neo4j -X POST localhost:7474/user/neo4j/password -H 'Content-type:application/json' -d '{"password":"secret"}'

This changes the password from neo4j to secret (something to NOT DO in production!) With that completed, you should be ready to run this guide.

Create a domain object

Create a new domain object to present a person.

src/main/java/hello/Person.java

link:complete/src/main/java/hello/Person.java[]

The Person has a first name and a last name. There is also an id object that is configured to be automatically generated so you don’t have to deal with that.

Permissions to access Neo4j

Neo4j Community Edition requires credentials to access it. This can be configured with a couple properties.

include complete/src/main/resources/application.properties[]

This includes the default username neo4j and the newly set password secret we picked earlier.

Warning
Do NOT store real credentials in your source repository. Instead, configure them in your runtime using Spring Boot’s property overrides.

With this in place, let’s wire this up and see what it looks like!

Create a Person repository

Next you need to create a simple repository.

src/main/java/hello/PersonRepository.java

link:complete/src/main/java/hello/PersonRepository.java[]

This repository is an interface and will allow you to perform various operations involving Person objects. It gets these operations by extending the PagingAndSortingRepositry interface defined in Spring Data Commons.

At runtime, Spring Data REST will create an implementation of this interface automatically. Then it will use the @RepositoryRestResource annotation to direct Spring MVC to create RESTful endpoints at /people.

Note
@RepositoryRestResource is not required for a repository to be exported. It is only used to change the export details, such as using /people instead of the default value of /persons.

Here you have also defined a custom query to retrieve a list of Person objects based on the lastName. You’ll see how to invoke it further down in this guide.

Make the application executable

Although it is possible to package this service as a traditional WAR file for deployment to an external application server, the simpler approach demonstrated below creates a standalone application. You package everything in a single, executable JAR file, driven by a good old Java main() method. Along the way, you use Spring’s support for embedding the Tomcat servlet container as the HTTP runtime, instead of deploying to an external instance.

src/main/java/hello/Application.java

link:complete/src/main/java/hello/Application.java[]

The @EnableNeo4jRepositories annotation activates Spring Data Neo4j. Spring Data Neo4j will create a concrete implementation of the PersonRepository and configure it to talk to an embedded Neo4j database using the Cypher query language.

Logging output is displayed. The service should be up and running within a few seconds.

Test the application

Now that the application is running, you can test it. You can use any REST client you wish. The following examples use the *nix tool curl.

First you want to see the top level service.

$ curl http://localhost:8080
{
  "_links" : {
    "people" : {
      "href" : "http://localhost:8080/people{?page,size,sort}",
      "templated" : true
    }
  }
}

Here you get a first glimpse of what this server has to offer. There is a people link located at http://localhost:8080/people. It has some options such as ?page, ?size, and ?sort.

Note
Spring Data REST uses the HAL format for JSON output. It is flexible and offers a convenient way to supply links adjacent to the data that is served.
$ curl http://localhost:8080/people
{
  "_links" : {
    "self" : {
      "href" : "http://localhost:8080/people{?page,size,sort}",
      "templated" : true
    },
    "search" : {
      "href" : "http://localhost:8080/people/search"
    }
  },
  "page" : {
    "size" : 20,
    "totalElements" : 0,
    "totalPages" : 0,
    "number" : 0
  }
}

There are currently no elements and hence no pages. Time to create a new Person!

$ curl -i -X POST -H "Content-Type:application/json" -d '{  "firstName" : "Frodo",  "lastName" : "Baggins" }' http://localhost:8080/people
HTTP/1.1 201 Created
Server: Apache-Coyote/1.1
Location: http://localhost:8080/people/0
Content-Length: 0
Date: Wed, 26 Feb 2014 20:26:55 GMT
  • -i ensures you can see the response message including the headers. The URI of the newly created Person is shown

  • -X POST signals this a POST used to create a new entry

  • -H "Content-Type:application/json" sets the content type so the application knows the payload contains a JSON object

  • -d '{ "firstName" : "Frodo", "lastName" : "Baggins" }' is the data being sent

Note
Notice how the previous POST operation includes a Location header. This contains the URI of the newly created resource. Spring Data REST also has two methods on RepositoryRestConfiguration.setReturnBodyOnCreate(…) and setReturnBodyOnCreate(…) which you can use to configure the framework to immediately return the representation of the resource just created.

From this you can query for all people:

$ curl http://localhost:8080/people
{
  "_links" : {
    "self" : {
      "href" : "http://localhost:8080/people{?page,size,sort}",
      "templated" : true
    },
    "search" : {
      "href" : "http://localhost:8080/people/search"
    }
  },
  "_embedded" : {
    "people" : [ {
      "firstName" : "Frodo",
      "lastName" : "Baggins",
      "_links" : {
        "self" : {
          "href" : "http://localhost:8080/people/0"
        }
      }
    } ]
  },
  "page" : {
    "size" : 20,
    "totalElements" : 1,
    "totalPages" : 1,
    "number" : 0
  }
}

The people object contains a list with Frodo. Notice how it includes a self link. Spring Data REST also uses Evo Inflector to pluralize the name of the entity for groupings.

You can query directly for the individual record:

$ curl http://localhost:8080/people/0
{
  "firstName" : "Frodo",
  "lastName" : "Baggins",
  "_links" : {
    "self" : {
      "href" : "http://localhost:8080/people/0"
    }
  }
}
Note
This might appear to be purely web based, but behind the scenes, there is an embedded Neo4j graph database. In production, you would probably connect to a stand alone Neo4j server.

In this guide, there is only one domain object. With a more complex system where domain objects are related to each other, Spring Data REST will render additional links to help navigate to connected records.

Find all the custom queries:

$ curl http://localhost:8080/people/search
{
  "_links" : {
    "findByLastName" : {
      "href" : "http://localhost:8080/people/search/findByLastName{?name}",
      "templated" : true
    }
  }
}

You can see the URL for the query including the HTTP query parameter name. If you’ll notice, this matches the @Param("name") annotation embedded in the interface.

To use the findByLastName query, do this:

$ curl http://localhost:8080/people/search/findByLastName?name=Baggins
{
  "_embedded" : {
    "people" : [ {
      "firstName" : "Frodo",
      "lastName" : "Baggins",
      "_links" : {
        "self" : {
          "href" : "http://localhost:8080/people/0"
        },
        "person" : {
          "href" : "http://localhost:8080/people/0"
        }
      }
    } ]
  },
  "_links" : {
    "self" : {
      "href" : "http://localhost:8080/people/search/findByLastName?name=Baggins"
    }
  }
}

Because you defined it to return List<Person> in the code, it will return all of the results. If you had defined it only return Person, it will pick one of the Person objects to return. Since this can be unpredictable, you probably don’t want to do that for queries that can return multiple entries.

You can also issue PUT, PATCH, and DELETE REST calls to either replace, update, or delete existing records.

$ curl -X PUT -H "Content-Type:application/json" -d '{ "firstName": "Bilbo", "lastName": "Baggins" }' http://localhost:8080/people/0
$ curl http://localhost:8080/people/0
{
  "firstName" : "Bilbo",
  "lastName" : "Baggins",
  "_links" : {
    "self" : {
      "href" : "http://localhost:8080/people/0"
    }
  }
}
$ curl -X PATCH -H "Content-Type:application/json" -d '{ "firstName": "Bilbo Jr." }' http://localhost:8080/people/0
$ curl http://localhost:8080/people/0
{
  "firstName" : "Bilbo Jr.",
  "lastName" : "Baggins",
  "_links" : {
    "self" : {
      "href" : "http://localhost:8080/people/0"
    }
  }
}
Note
PUT replaces an entire record. Fields not supplied will be replaced with null. PATCH can be used to update a subset of items.

You can delete records:

$ curl -X DELETE http://localhost:8080/people/0
$ curl http://localhost:8080/people
{
  "_links" : {
    "self" : {
      "href" : "http://localhost:8080/people{?page,size,sort}",
      "templated" : true
    },
    "search" : {
      "href" : "http://localhost:8080/people/search"
    }
  },
  "page" : {
    "size" : 20,
    "totalElements" : 0,
    "totalPages" : 0,
    "number" : 0
  }
}

A very convenient aspect of this hypermedia-driven interface is how you can discover all the RESTful endpoints using curl (or whatever REST client you are using). There is no need to exchange a formal contract or interface document with your customers.

Summary

Congratulations! You’ve just developed an application with a hypermedia-based RESTful front end and a Neo4j-based back end.