How do you create a REST client for Java?

With JSR 311 and its implementations we have a powerful standard for exposing Java objects via REST. However on the client side there seems to be something missing that is comparable to Apache Axis for SOAP - something that hides the web service and marshals the data transparently back to Java objects.

How do you create Java RESTful clients? Using HTTPConnection and manual parsing of the result? Or specialized clients for e.g. Jersey or Apache CXR?

This is an old question (2008) so there are many more options now than there were then:

• Apache CXF has three different REST Client options
• Jersey (mentioned above).
• Spring RestTemplate superceded by Spring WebClient
• Commons HTTP Client build your own for older Java projects.

UPDATES (projects still active in 2020):

• Apache HTTP Components (4.2) Fluent adapter - Basic replacement for JDK, used by several other candidates in this list. Better than old Commons HTTP Client 3 and easier to use for building your own REST client. You'll have to use something like Jackson for JSON parsing support and you can use HTTP components URIBuilder to construct resource URIs similar to Jersey/JAX-RS Rest client. HTTP components also supports NIO but I doubt you will get better performance than BIO given the short requestnature of REST. Apache HttpComponents 5 has HTTP/2 support.
• OkHttp - Basic replacement for JDK, similar to http components, used by several other candidates in this list. Supports newer HTTP protocols (SPDY and HTTP2). Works on Android. Unfortunately it does not offer a true reactor-loop based async option (see Ning and HTTP components above). However if you use the newer HTTP2 protocol this is less of a problem (assuming connection count is problem).
• Ning Async-http-client - provides NIO support. Previously known as Async-http-client by Sonatype.
• Feign wrapper for lower level http clients (okhttp, apache httpcomponents). Auto-creates clients based on interface stubs similar to some Jersey and CXF extensions. Strong spring integration.
• Retrofit - wrapper for lower level http clients (okhttp). Auto-creates clients based on interface stubs similar to some Jersey and CXF extensions.
• Volley wrapper for jdk http client, by google
• google-http wrapper for jdk http client, or apache httpcomponents, by google
• Unirest wrapper for jdk http client, by kong
• Resteasy JakartaEE wrapper for jdk http client, by jboss, part of jboss framework
• jcabi-http wrapper for apache httpcomponents, part of jcabi collection
• restlet wrapper for apache httpcomponents, part of restlet framework
• rest-assured wrapper with asserts for easy testing

A caveat on picking HTTP/REST clients. Make sure to check what your framework stack is using for an HTTP client, how it does threading, and ideally use the same client if it offers one. That is if your using something like Vert.x or Play you may want to try to use its backing client to participate in whatever bus or reactor loop the framework provides... otherwise be prepared for possibly interesting threading issues.

As I mentioned in this thread I tend to use Jersey which implements JAX-RS and comes with a nice REST client. The nice thing is if you implement your RESTful resources using JAX-RS then the Jersey client can reuse the entity providers such as for JAXB/XML/JSON/Atom and so forth - so you can reuse the same objects on the server side as you use on the client side unit test.

For example here is a unit test case from the Apache Camel project which looks up XML payloads from a RESTful resource (using the JAXB object Endpoints). The resource(uri) method is defined in this base class which just uses the Jersey client API.

e.g.

    clientConfig = new DefaultClientConfig();
    client = Client.create(clientConfig);

    resource = client.resource("http://localhost:8080");
    // lets get the XML as a String
    String text = resource("foo").accept("application/xml").get(String.class);        

BTW I hope that future version of JAX-RS add a nice client side API along the lines of the one in Jersey

You can use the standard Java SE APIs:

private void updateCustomer(Customer customer) { 
    try { 
        URL url = new URL("http://www.example.com/customers"); 
        HttpURLConnection connection = (HttpURLConnection) url.openConnection(); 
        connection.setDoOutput(true); 
        connection.setInstanceFollowRedirects(false); 
        connection.setRequestMethod("PUT"); 
        connection.setRequestProperty("Content-Type", "application/xml"); 
 
        OutputStream os = connection.getOutputStream(); 
        jaxbContext.createMarshaller().marshal(customer, os); 
        os.flush(); 
 
        connection.getResponseCode(); 
        connection.disconnect(); 
    } catch(Exception e) { 
        throw new RuntimeException(e); 
    } 
} 

Or you can use the REST client APIs provided by JAX-RS implementations such as Jersey. These APIs are easier to use, but require additional jars on your class path.

WebResource resource = client.resource("http://www.example.com/customers"); 
ClientResponse response = resource.type("application/xml");).put(ClientResponse.class, "<customer>...</customer."); 
System.out.println(response); 

For more information see:

• http://bdoughan.blogspot.com/2010/08/creating-restful-web-service-part-55.html

If you only wish to invoke a REST service and parse the response you can try out Rest Assured

// Make a GET request to "/lotto"
String json = get("/lotto").asString()
// Parse the JSON response
List<String> winnderIds = with(json).get("lotto.winners.winnerId");

// Make a POST request to "/shopping"
String xml = post("/shopping").andReturn().body().asString()
// Parse the XML
Node category = with(xml).get("shopping.category[0]");

You can also check Restlet which has full client-side capabilities, more REST oriented that lower-level libraries such as HttpURLConnection or Apache HTTP Client (which we can leverage as connectors).

Best regards, Jerome Louvel

You could try Rapa. Let us know your feedback about the same. And feel free to log issues or expected features.

I'd like to point out 2 more options:

• Restfulie, based on the VRaptor web framework, has both server and client side implementations with very good Hypermedia support.
• RESTEasy has a JAX-RS proxy based client implementation.

Try JdkRequest from jcabi-http (I'm a developer). This is how it works:

String body = new JdkRequest("http://www.google.com")
  .header("User-Agent", "it's me")
  .fetch()
  .body()

Check this blog post for more details: http://www.yegor256.com/2014/04/11/jcabi-http-intro.html

I've recently tried Retrofit Library from square, Its great and you can call your rest API very easily. Annotation based configuration allows us to get rid of lot of boiler plate coding.

OkHttp is lightweight and powerful when combined with Retrofit as well. This works well for general Java use as well as on Android.

OkHttp: http://square.github.io/okhttp/

public static final MediaType JSON
    = MediaType.parse("application/json; charset=utf-8");

OkHttpClient client = new OkHttpClient();

String post(String url, String json) throws IOException {
  RequestBody body = RequestBody.create(JSON, json);
  Request request = new Request.Builder()
      .url(url)
      .post(body)
      .build();
  Response response = client.newCall(request).execute();
  return response.body().string();
}

Retrofit: http://square.github.io/retrofit/

public interface GitHubService {
  @GET("/users/{user}/repos")
  Call<List<Repo>> listRepos(@Path("user") String user);
}

I use Apache HTTPClient to handle all the HTTP side of things.

I write XML SAX parsers for the XML content that parses the XML into your object model. I believe that Axis2 also exposes XML -> Model methods (Axis 1 hid this part, annoyingly). XML generators are trivially simple.

It doesn't take long to code, and is quite efficient, in my opinion.

Since no one mentioned, here is another one: Feign, which is used by Spring Cloud.

Though its simple to create a HTTP client and make a reuest. But if you want to make use of some auto generated clients, You can make use of WADL to describe and generate code.

You can use RestDescribe to generate and compile WSDL, you can generate clients in php, ruby, python, java and C# using this. It generates clean code and there is a good change that you have to tweak it a bit after code generation, you can find good documentation and underlying thoughts behind the tool here.

There are few interesting and useful WADL tools mentioned on wintermute.

I wrote a library that maps a java interface to a remote JSON REST service:

https://github.com/ggeorgovassilis/spring-rest-invoker

public interface BookService {
   @RequestMapping("/volumes")
   QueryResult findBooksByTitle(@RequestParam("q") String q);

   @RequestMapping("/volumes/{id}")
   Item findBookById(@PathVariable("id") String id);
}

Examples of jersey Rest client :
Adding dependency :

         <!-- jersey -->
	<dependency>
		<groupId>com.sun.jersey</groupId>
		<artifactId>jersey-json</artifactId>
		<version>1.8</version>
	</dependency>
   <dependency>
		<groupId>com.sun.jersey</groupId>
		<artifactId>jersey-server</artifactId>
		<version>1.8</version>
	</dependency>
	
<dependency>
	<groupId>com.sun.jersey</groupId>
	<artifactId>jersey-client</artifactId>
	<version>1.8</version>
</dependency>

  	<dependency>
	<groupId>org.json</groupId>
	<artifactId>json</artifactId>
	<version>20090211</version>
</dependency>

ForGetMethod and passing two parameter :

          Client client = Client.create();
           WebResource webResource1 = client
						.resource("http://localhost:10102/NewsTickerServices/AddGroup/"
								+ userN + "/" + groupName);

				ClientResponse response1 = webResource1.get(ClientResponse.class);
				System.out.println("responser is" + response1);

GetMethod passing one parameter and Getting a Respone of List :

       Client client = Client.create();

        WebResource webResource1 = client
			        .resource("http://localhost:10102/NewsTickerServices/GetAssignedUser/"+grpName);	
	//value changed
	String response1 = webResource1.type(MediaType.APPLICATION_JSON).get(String.class);
 
    List <String > Assignedlist =new ArrayList<String>();
     JSONArray jsonArr2 =new JSONArray(response1);
    for (int i =0;i<jsonArr2.length();i++){
    	
    	Assignedlist.add(jsonArr2.getString(i));	
    }

In Above It Returns a List which we are accepting as a List and then converting it to Json Array and then Json Array to List .

If Post Request passing Json Object as Parameter :

   Client client = Client.create();
	WebResource webResource = client
			.resource("http://localhost:10102/NewsTickerServices/CreateJUser");
	// value added

	ClientResponse response = webResource.type(MediaType.APPLICATION_JSON).post(ClientResponse.class,mapper.writeValueAsString(user));

	if (response.getStatus() == 500) {

		context.addMessage(null, new FacesMessage("User already exist "));
	}

I used RestAssured most of the time to parse rest service response and test the services. Apart from Rest Assured, I used below libraries too to communicate with Resful services.

a. Jersey Rest Client

b. Spring RestTemplate

c. Apache HTTP Client

Try looking at http-rest-client

https://github.com/g00dnatur3/http-rest-client

Here is a simple example:

RestClient client = RestClient.builder().build();
String geocoderUrl = "http://maps.googleapis.com/maps/api/geocode/json"
Map<String, String> params = Maps.newHashMap();
params.put("address", "beverly hills 90210");
params.put("sensor", "false");
JsonNode node = client.get(geocoderUrl, params, JsonNode.class);

The library takes care of json serialization and binding for you.

Here is another example,

RestClient client = RestClient.builder().build();
String url = ...
Person person = ...
Header header = client.create(url, person);
if (header != null) System.out.println("Location header is:" + header.value());

And one last example,

RestClient client = RestClient.builder().build();
String url = ...
Person person = client.get(url, null, Person.class); //no queryParams

Cheers!

I am currently using https://github.com/kevinsawicki/http-request I like their simplicity and the way examples are shown, but mostly I was sold when I read:

> What are the dependencies? > > None. The goal of this library is to be a single class class with some inner static classes. The test project does require Jetty in order to test requests against an actual HTTP server implementation.

which sorted out some problems on a java 1.6 project. As for decoding json into objects gson is just invincible :)