Stateful interactions are based on the concept of explicit state transfer.
Several techniques exist to exchange state, such as URI rewriting, cookies, and hidden form fields. State can be embedded in response messages to point to valid future states of the interaction. The Java EE 6 Tutorial. The following principles encourage RESTful applications to be simple, lightweight, and fast: Getting Started with Web Applications 4.
JavaServer Faces Technology 5. Introduction to Facelets 6. Using Converters, Listeners, and Validators 9. Developing with JavaServer Faces Technology Advanced Topics and Example Configuring JavaServer Faces Applications Java Servlet Technology Uploading Files with Java Servlet Technology Introduction to Web Services Getting Started with Enterprise Beans Running the Enterprise Bean Examples In a true REST web service, we would decide on the best database or persistence framework that supports our domain model and design a persistence layer interface to use to interact with this database.
For example, we could select a Neo4j database if our data was well-suited for a graph domain model, or MongoDB if our domain model fits nicely into collections. In the case of our system, for simplicity, we will use an in-memory persistence layer. Although there are various useful in-memory databases, our model is simple enough to create the in-memory database ourselves.
In doing so, we will see the basic functionality of a database attached to a REST service, as well as understand the simple interfaces that are common among repositories in RESTful services. At this point in our design, we have three discrete sections of our system: This set of three sections is so common, it has its own name: Whatsmore, Martin Fowler has written an entire book, Patterns of Enterprise Architecture , on the patterns that surround this application architecture.
The three tiers in this architecture are 1 presentation, 2 domain, and 3 data source used interchangeably with persistence layer. In our case, our REST endpoints map to the presentation layer, our order domain model maps to the domain layer, and our in-memory database maps to the data source layer.
Getting Started · Building a RESTful Web Service
Although these three layers are usually depicted with one stacked on top of the other, with the presentation layer at the top, closest to the user, the domain layer in the middle, and the data source layer on the bottom, it can be more helpful to look at this architecture in terms of its interactions, as illustrated in the following diagram.
There is an important addition that is made to our architecture: Domain objects are not sent directly to the user. Instead, they are wrapped in resources and the resources are provided to the user. This provides a level of indirection between the domain object and how we present the domain object to the user.
For example, if we wish to present the user with a different name for a field in our domain model say orderName instead of simply name , we can do so using a resource. Although this level of indirection is very useful in decoupling our presentation from the domain model, it does allow duplication to sneak in. In most cases, the resource will resemble the interface of the domain object, with a few minor additions. This issue is addressed later when we implement our presentation layer. The resource object also provides an apt place for us to introduce our hypermedia links.
According to the Richardson model for REST web services , hypermedia-driven services are the highest capability level of a REST application and provide important information associated with the resource data. For example, we can provide links for deleting or updating the resource, which removes the need for the client consuming our REST web service to know the REST endpoints for these actions. In practice, the returned resource deserialized to JSON may resemble the following:.
Instead, it can simply use the links provided in our hypermedia-driven response. Not only does this reduces the logic necessary for interacting with our REST web service no longer do the URLs need to be built , but it also encapsulates the logic for the construction of the URLs. For example, suppose we change our REST service to require a query parameter, such as sorting: Although generating these links could be tedious and subject to a large number of bugs i. This topic will be explored further when we delve into the implementation of our presentation layer.
Before moving to the implementation of our web service, we must pull our design together and devise a plan of action to create it. At the moment, we have a single domain object, Order, instances of whom will be persisted in an in-memory database and served up within a resource to clients using our REST endpoints. This design leaves us with four main steps:. In Part 2 , we will work on implementing the data source and domain layers, which will lay the foundation for implementing the RESTful interface of our web service. Asynchronous and Event-Based Application Design.
What you’ll need
Over a million developers have joined DZone. In the first part of this series, we take a look at how the design of the web service we'll be creating, and the tech we'll be using to there.
The resource is never changed via a GET request, e. The operations are idempotent. They can get repeated without leading to different results. Download the Jersey distribution as zip file from the Jersey download site. The zip contains the Jersey implementation JAR and its core dependencies. This is required for the following tutorials. Make also sure that you followed the Eclipse Buildship Tutorial to enable Gradle support for Eclipse.
If you have not yet created a Gradle project, you can follow the Buildship tutorial to create one. Since we want to create a web application, we want a war file and not a jar file which would be created by Gradle with the Java plugin. The eclipse-wtp plugin helps you to generate the Eclipse WTP project files. Now, add a new folder with the name WebContent to your projects root. The next step is to add a xml file with the name web.
Creating a REST Web Service With Java and Spring (Part 1)
To do so menu: Now the newly created folders with the web. This will add various new tasks to your Gradle Tasks view. The following description assumes that you are familiar with creating web applications in Eclipse. Create a new Gradle project named com. You can follow Required setup for Gradle and Eclipse web projects to get started. This class register itself as a get resource via the GET annotation. It also defines via the Path annotation that its service is available under the hello URL. To see the text version, you can use tool like curl.
This property must point to your resources classes. To run your web application in Eclipse, make sure to run the gradle task eclipseWtp first. This URL is derived from the context root value in the projects properties Web Project Settings by default, this is your application name , augmented with the servlet-mapping URL-pattern and the hello Path annotation from your class file. You should get the message "Hello Jersey". As we are using Gradle, if you want to update the context root include the following in your build. The browser requests the HTML representation of your resource.
In the next chapter we are going to write a client which will read the XML representation. Jersey contains a REST client library which can be used for testing or to build a real client in Java.
The usage of this library is demonstrated in the following tutorial. Create a new Java gradle project with com. You can continue this tutorial without reading these tutorials, but they contain more background information. To enable JSON support, add the following dependency to your build.
Create the following resource class. This class simply returns an instance of the Todo class. Run you web application in Eclipse and validate that you can access your service. Your application should be available under the following URL.