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This repository contains the guide documentation source. To view the guide in published form, view it on the Open Liberty website. |
Learn how to create a REST service with JAX-RS, JSON-B, and Open Liberty.
You will learn how to build and test a simple REST service with JAX-RS and JSON-B, which will expose
the JVM’s system properties. The REST service will respond to GET requests made to the http://localhost:9080/LibertyProject/System/properties URL.
The service responds to a GET request with a JSON representation of the system properties, where
each property is a field in a JSON object like this:
{
"os.name":"Mac",
"java.version": "1.8"
}The design of an HTTP API is essential when creating a web application. The REST API has become the go-to architectural style for building an HTTP API. The JAX-RS API offers functionality for creating, reading, updating, and deleting exposed resources. The JAX-RS API supports the creation of RESTful web services that come with desirable properties, such as performance, scalability, and modifiability.
Check out the service at the http://localhost:9080/LibertyProject/System/properties URL.
Navigate to the start directory to begin.
JAX-RS has two key concepts for creating REST APIs. The most obvious one is the resource itself, which is modelled as a class. The second is a JAX-RS application, which groups all exposed resources under a common path. You can think of the JAX-RS application as a wrapper for all of your resources.
Replace theSystemApplicationclass.src/main/java/io/openliberty/guides/rest/SystemApplication.java
The SystemApplication class extends the Application class, which associates all JAX-RS resource classes in the WAR file with this JAX-RS application. These resources become available under the common path that’s specified with the @ApplicationPath
annotation. The @ApplicationPath annotation has a value that indicates the path in the WAR file that
the JAX-RS application accepts requests from.
SystemApplication.java
link:finish/src/main/java/io/openliberty/guides/rest/SystemApplication.java[role=include]In JAX-RS, a single class should represent a single resource, or a group of resources of the same type. In this application, a resource might be a system property, or a set of system properties. It is easy to have a single class handle multiple different resources, but keeping a clean separation between types of resources helps with maintainability in the long run.
Create thePropertiesResourceclass.src/main/java/io/openliberty/guides/rest/PropertiesResource.java
This resource class has quite a bit of code in it, so let’s break it down into manageable chunks.
The @Path annotation on the class indicates that this resource responds to the properties path
in the JAX-RS application. The @ApplicationPath annotation in the SystemApplication class together with
the @Path annotation in this class indicates that the resource is available at the System/properties
path.
JAX-RS maps the HTTP methods on the URL to the methods of the class by using annotations.
Your application uses the GET annotation to map an HTTP GET request
to the System/properties path.
The @GET annotation on the method indicates that this method is to be called for the HTTP GET
method. The @Produces annotation indicates the format of the content that will be returned. The
value of the @Produces annotation will be specified in the HTTP Content-Type response header.
For this application, a JSON structure is to be returned. The desired Content-Type for a JSON
response is application/json with MediaType.APPLICATION_JSON instead of the String content type. Using a constant such as MediaType.APPLICATION_JSON is better because if there’s a spelling error, a compile failure occurs.
JAX-RS supports a number of ways to marshal JSON. The JAX-RS 2.1 specification mandates JSON-Binding
(JSON-B). The method body returns the result of System.getProperties(), which is of type java.util.Properties. Since the method
is annotated with @Produces(MediaType.APPLICATION_JSON), JAX-RS uses JSON-B to automatically convert the returned object
to JSON data in the HTTP response.
PropertiesResource.java
link:finish/src/main/java/io/openliberty/guides/rest/PropertiesResource.java[role=include]SystemApplication.java
link:finish/src/main/java/io/openliberty/guides/rest/SystemApplication.java[role=include]To get the service running, the Liberty server needs to be correctly configured.
Replace the server configuration file.
src/main/liberty/config/server.xml
server.xml
link:finish/src/main/liberty/config/server.xml[role=include]The configuration does the following actions:
-
Configures the server to enable JAX-RS. This is specified in the
featureManagerelement. -
Configures the server to resolve the HTTP port numbers from variables, which are then specified in the Maven
pom.xmlfile. This is specified in the<httpEndpoint/>element. Variables use the${variableName}syntax. -
Configures the server to run the produced web application on a context root specified in the
pom.xmlfile. This is specified in the<webApplication/>element.
pom.xml
link:finish/pom.xml[role=include]The variables that are being used in the server.xml file are provided by the properties set in the Maven pom.xml file. The properties must be formatted as liberty.var.variableName.
Check out the service that you created at the http://localhost:9080/LibertyProject/System/properties URL.
You can test this service manually by starting a server and pointing a web browser at the http://localhost:9080/LibertyProject/System/properties URL. However, automated tests are a much better approach because they trigger a failure if a change introduces a bug. JUnit and the JAX-RS Client API provide a simple environment to test the application.
You can write tests for the individual units of code outside of a running application server, or they can be written to call the application server directly. In this example, you will create a test that does the latter.
Create theEndpointITclass.src/test/java/it/io/openliberty/guides/rest/EndpointIT.java
EndpointIT.java
link:finish/src/test/java/it/io/openliberty/guides/rest/EndpointIT.java[role=include]This test class has more lines of code than the resource implementation. This situation is common.
The test method is indicated with the @Test annotation.
pom.xml
link:finish/pom.xml[role=include]The test code needs to know some information about the application to make requests. The server port and the application context root are key, and are dictated by the server configuration. While this information can be hardcoded, it is better to specify it in a single place like the Maven pom.xml file. Refer to the pom.xml file to see how the application information such as the default.http.port, default.https.port and app.context.root elements are provided in the file.
These Maven properties are then passed to the Java test program as the <systemPropertyVariables/> element in the pom.xml file.
Getting the values to create a representation of the URL is simple. The test class uses the getProperty method
to get the application details.
To call the JAX-RS service using the JAX-RS client, first create a WebTarget object by calling
the target method that provides the URL. To cause the HTTP request to occur, the request().get() method
is called on the WebTarget object. The get method
call is a synchronous call that blocks until a response is received. This call returns a Response
object, which can be inspected to determine whether the request was successful.
The first thing to check is that a 200 response was received. The JUnit assertEquals method can be used for this check.
Check the response body to ensure it returned the right information. Since the client and the server
are running on the same machine, it is reasonable to expect that the system properties for the local
and remote JVM would be the same. In this case, an assertEquals assertion is made so that the os.name system property
for both JVMs is the same. You can write additional assertions to check for more values.
You will see the following output:
-------------------------------------------------------
T E S T S
-------------------------------------------------------
Running it.io.openliberty.guides.rest.EndpointIT
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 2.884 sec - in it.io.openliberty.guides.rest.EndpointIT
Results :
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0To see whether the tests detect a failure, add an assertion that you know fails, or change the existing
assertion to a constant value that doesn’t match the os.name system property.
You just developed a REST service in Open Liberty by using JAX-RS and JSON-B.