HTTP Client API is a Java based framework for communication with Web Services.

Description

HTTP Client provides the following capabilities:

• easy way of creating and configuring of HTTP requests,
• synchronous and asynchronous executing of request,
• performing request pre-processing and response post-processing.

Creating and configuring HTTP request

The following code illustrates typical scheme of creating and configuring a client request:

        // default client builder
        HttpClientBuilder clientBuilder = HttpClientBuilder.getInstance();

        // additional configuration of client builder
        clientBuilder.addRequestFilter(new UserRequestFilter());
        clientBuilder.addResponseFilter(new UserResponseFilter());

        // additional connection option
        ConnectionOption<Integer> timeoutOption = new ConnectionOption<>("Timeout", 2000);
        clientBuilder.addConnectionOptions(timeoutOption);

        // configured client instance
        // client instance is the main entry point which is used for preparing client requests.
        HttpClient client = clientBuilder.build();

        // construct request builder
        HttpRequestBuilder requestBuilder = client.build("http://example.org");
        requestBuilder.setHeader(HttpHeader.ACCEPT, "text/plain");
        requestBuilder.setMethod(HttpMethod.GET);

        // prepared client request is ready for execution
        HttpRequest request = requestBuilder.build();
        

HTTP Client API supports fluent API model. The above code can be written as follows:

        HttpClient client = HttpClientBuilder.getInstance()
                .addRequestFilter(new UserRequestFilter())
                .addResponseFilter(new UserResponseFilter())
                .addConnectionOptions(new ConnectionOption<>("Timeout", 2000))
                .build();

        HttpRequest request = client.build("http://example.org")
                .setHeader(HttpHeader.ACCEPT, "text/plain")
                .setMethod(HttpMethod.GET)
                .build();
        

Request invocation

HTTP Client API allows to use synchronous or asynchronous execution of a client request. The following example illustrates the synchronous(blocking) execution of a request:

        HttpResponse response = clientRequest.invoke();
        if (HttpResponse.OK == response.getResponseCode()) {
            // handle the response
        }
        

Client application must provide a HttpResponseListener implementation in case of asynchronous execution of a request:

        clientRequest.invoke(
                new HttpResponseListener() {
                    @Override
                    public void handle(HttpResponse response) {
                        // handle the response
                    }
                    @Override
                    public void failed(HttpClientException cause) {
                        // handle the exception
                    }
        });
        

Filters

Filters are used in order to provide capabilities as logging, authentication, etc. Filters can be registered the following manner:

        public class UserAgentFilter implements HttpRequestFilter {
            private final String userAgent;

            public UserAgentFilter() {
                userAgent = "Profile/" + System.getProperty("microedition.profiles") +
                            " Configuration/" + System.getProperty("microedition.configuration");
            }

            @Override
            public void filter(ProcessedHttpRequest request, HttpRequestProcessingContext processingContext) {
                if (!request.getHeaders().contains(HttpHeader.USER_AGENT)) {
                    request.getHeaders().setHeaderValue(HttpHeader.USER_AGENT, userAgent);
                }
            }
        }

        HttpClientBuilder clientBuilder = HttpClientBuilder.getInstance()
                .addRequestFilter(new UserAgentFilter());
        

References:

• [RFC2616] Hypertext Transfer Protocol -- HTTP/1.1. Available at: http://www.ietf.org/rfc/rfc2616.txt
• [RFC3986] Uniform Resource Identifier (URI): Generic Syntax. Available at: http://www.ietf.org/rfc/rfc3986.txt
• [GCF8] Generic Connection Framework.