RESTful Requests

As a review, the four types of HTTP methods called by REST requests are

• GET - retrieve a resource
• PUT - replace a resource
• POST - create a new resource
• DELETE - delete a resource

REST Objects

The Apache HttpComponents library allows for the creation of different REST requests. The basic structure for all the requests it to create an HTTPClient object, an appropriate URI

// Create HTTP client
HttpClient client = new DefaultHttpClient();

// Create URI
URI uri;
uri = URIUtils.createURI("http", host , -1, service, 
            URLEncodedUtils.format(params, "UTF-8"), null);

Once the client and URI are created, an appropriate REST object can be instantiated along with an HTTPEntity payload if necessary.

HTTPGet

The HTTPGet class produces GET requests with optional payload

// Create HTTP GET request from URI
HttpGet request = new HttpGet(uri);

// TODO: Create reqEntity payload object for request as needed  

// Set payload in request
// request.setEntity(reqEntity);

// Execute request and get response
HttpResponse response;
response = client.execute(request);

// Get payload from response
HttpEntity respEntity = response.getEntity();

// TODO: Process response payload as appropriate

HTTPPut

The HTTPPut class produces PUT requests with optional payload

// Create HTTP PUT request from URI
HttpPut request = new HttpPut(uri);

// TODO: Create reqEntity payload object for request as needed  

// Set payload in request
// request.setEntity(reqEntity);

// Execute request and get response
HttpResponse response;
response = client.execute(request);

// Get payload from response
HttpEntity respEntity = response.getEntity();

// TODO: Process response payload as appropriate

HTTPPost

The HTTPPost class produces POST requests with optional payload

// Create HTTP POST request from URI
HttpPost request = new HttpPost(uri);

// TODO: Create reqEntity payload object for request as needed  

// Set payload in request
// request.setEntity(reqEntity);

// Execute request and get response
HttpResponse response;
response = client.execute(request);

// Get payload from response
HttpEntity respEntity = response.getEntity();

// TODO: Process response payload as appropriate

HTTPDelete

The HTTPDelete class produces DELETE requests (note no payload can be sent with a DELETE request)

// Create HTTP DELETE request from URI
HttpDelete request = new HttpDelete(uri);

// Execute request and get response
HttpResponse response;
response = client.execute(request);

// Get payload from response
HttpEntity respEntity = response.getEntity();

// TODO: Process response payload as appropriate

HttpEntity

The HTTPEntity class is used with the GET, PUT, and POST classes to send additional information in the requests and responses. In particular, the getContent() method can be used on an entity object to retrieve the data which can then be converted as needed. For example, if the contents is a input stream,

// Get payload from response
HttpEntity respEntity = response.getEntity();

// Process response payload if non-empty
if (respEntity != null) {
   // Get stream from entity
   InputStream s = respEntity.getContent();

   // Parse stream
   BufferedReader r = new BufferedReader(new InputStreamReader(s));
   StringBuider str = new StringBuilder();
   String line = null;
   while ((line = reader.readLine()) != null) {
      str.append(line + "\n");
   }
   s.close();
   String text = str.toString();
}

Often the HTTPEntity object may contain XML that we can subsequently parse which we will see later in the course.