buzzardo / gs-accessing-gemfire-data-rest

Accessing GemFire Data with REST :: Learn how to work with RESTful, hypermedia-based data persistence using Spring Data REST.

Table of Contents

• What you’ll build
• What you’ll need
• Create a domain object
• Create a Person Repository
• Make the application executable
• Test the application
• Summary
• See Also

This guide walks you through the process of creating an application that accesses Pivotal GemFire data through a hypermedia-based REST-ful frontend.

What you’ll build

You’ll build a Spring Web application that let’s you create and retrieve Person objects stored in the Pivotal GemFire In-Memory Data Grid using Spring Data REST. Spring Data REST takes the features of Spring HATEOAS and Spring Data for Pivotal GemFire and combines them together automatically.

Note	Spring Data REST also supports Spring Data JPA, Spring Data MongoDB and Spring Data Neo4j as backend data stores, but those are not part of this guide.

Tip	For more general knowledge of Pivotal GemFire concepts and accessing data from Pivotal GemFire, read through the guide, Accessing Data with Pivotal GemFire.

What you’ll need

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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[role=include]

The Person has a first and last name. Pivotal GemFire domain objects need an id, so an AtomicLong is being used to increment with each Person object creation.

Create a Person Repository

Next, you need to create a simple Repository to persist/access Person objects stored in Pivotal GemFire.

src/main/java/hello/PersonRepository.java

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

This Repository is an interface and will allow you to perform various data access operations (e.g. basic CRUD and simple queries) involving Person objects. It gets these operations by extending CrudRepository.

At runtime, Spring Data for Pivotal GemFire will create an implementation of this interface automatically. Then, Spring Data REST will use the @RepositoryRestResource annotation to direct Spring MVC to create REST-ful 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 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 servlet container.

src/main/java/hello/Application.java

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The @EnableGemfireRepositories annotation activates Spring Data for Pivotal GemFire Repositories. Spring Data for Pivotal GemFire will create a concrete implementation of the PersonRepository interface and configure it to talk to an embedded instance of Pivotal GemFire.

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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 uses the *nix tool curl.

First you want to see the top level service.

$ curl http://localhost:8080
{
  "_links" : {
    "people" : {
      "href" : "http://localhost:8080/people"
    }
  }
}

Here you get your first glimpse of what this server has to offer. There is a people link located at http://localhost:8080/people. Spring Data for Pivotal GemFire doesn’t support pagination like the other Spring Data REST guides so there are no extra navigational links.

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" : {
    "search" : {
      "href" : "http://localhost:8080/people/search"
    }
  }
}

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/1
Content-Length: 0
Date: Wed, 05 Mar 2014 20:16:11 GMT

• -i ensures you can see the response message including the headers. The URI of the newly created Person is shown

• -X POST issues a POST HTTP request 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" : {
    "search" : {
      "href" : "http://localhost:8080/people/search"
    }
  },
  "_embedded" : {
    "persons" : [ {
      "firstName" : "Frodo",
      "lastName" : "Baggins",
      "_links" : {
        "self" : {
          "href" : "http://localhost:8080/people/1"
        }
      }
    } ]
  }
}

The people collection resource 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/1
{
  "firstName" : "Frodo",
  "lastName" : "Baggins",
  "_links" : {
    "self" : {
      "href" : "http://localhost:8080/people/1"
    }
  }
}

Note	This might appear to be purely web based, but behind the scenes, it is talking to an embedded Pivotal GemFire database.

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" : {
    "persons" : [ {
      "firstName" : "Frodo",
      "lastName" : "Baggins",
      "_links" : {
        "self" : {
          "href" : "http://localhost:8080/people/1"
        }
      }
    } ]
  }
}

Because you defined it to return List<Person> in the code, it will return all of the results. If you had defined it to only return Person, it would 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/1
$ curl http://localhost:8080/people/1
{
  "firstName" : "Bilbo",
  "lastName" : "Baggins",
  "_links" : {
    "self" : {
      "href" : "http://localhost:8080/people/1"
    }
  }
}

$ curl -X PATCH -H "Content-Type:application/json" -d '{ "firstName": "Bilbo Jr." }' http://localhost:8080/people/1
$ curl http://localhost:8080/people/1
{
  "firstName" : "Bilbo Jr.",
  "lastName" : "Baggins",
  "_links" : {
    "self" : {
      "href" : "http://localhost:8080/people/1"
    }
  }
}

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/1
$ curl http://localhost:8080/people
{
  "_links" : {
    "search" : {
      "href" : "http://localhost:8080/people/search"
    }
  }
}

A very convenient aspect of this hypermedia-driven interface is how you can discover all the REST-ful 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 frontend and a Pivotal GemFire-based backend.

See Also

The following guides may also be helpful:

• Accessing JPA Data with REST

• Accessing MongoDB Data with REST

• Accessing data with MySQL

• Accessing Neo4j Data with REST

• Consuming a RESTful Web Service

• Consuming a RESTful Web Service with AngularJS

• Consuming a RESTful Web Service with jQuery

• Consuming a RESTful Web Service with rest.js

• Securing a Web Application

• Building REST services with Spring

• Building an Application with Spring Boot

• Creating API Documentation with Restdocs

• Enabling Cross Origin Requests for a RESTful Web Service

• Building a Hypermedia-Driven RESTful Web Service

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