HttpClient(4.3.5) - HTTP Protocol Interceptors

標籤：

The HTTP protocol interceptor is a routine that implements a specific aspect of the HTTP protocol. Usually protocol interceptors are expected to act upon one specific header or a group of related headers of the incoming message, or populate the outgoing message with one specific header or a group of related headers. Protocol interceptors can also manipulate content entities enclosed with messages - transparent content compression / decompression being a good example. Usually this is accomplished by using the ‘Decorator‘ pattern where a wrapper entity class is used to decorate the original entity. Several protocol interceptors can be combined to form one logical unit.

Protocol interceptors can collaborate by sharing information - such as a processing state - through the HTTP execution context. Protocol interceptors can use HTTP context to store a processing state for one request or several consecutive requests.

Usually the order in which interceptors are executed should not matter as long as they do not depend on a particular state of the execution context. If protocol interceptors have interdependencies and therefore must be executed in a particular order, they should be added to the protocol processor in the same sequence as their expected execution order.

Protocol interceptors must be implemented as thread-safe. Similarly to servlets, protocol interceptors should not use instance variables unless access to those variables is synchronized.

This is an example of how local context can be used to persist a processing state between consecutive requests:

CloseableHttpClient httpclient = HttpClients.custom()        .addInterceptorLast(new HttpRequestInterceptor() {            public void process(                    final HttpRequest request,                    final HttpContext context) throws HttpException, IOException {                AtomicInteger count = (AtomicInteger) context.getAttribute("count");                request.addHeader("Count", Integer.toString(count.getAndIncrement()));            }        })        .build();AtomicInteger count = new AtomicInteger(1);HttpClientContext localContext = HttpClientContext.create();localContext.setAttribute("count", count);HttpGet httpget = new HttpGet("http://localhost/");for (int i = 0; i < 10; i++) {    CloseableHttpResponse response = httpclient.execute(httpget, localContext);    try {        HttpEntity entity = response.getEntity();    } finally {        response.close();    }}

 

HttpClient(4.3.5) - HTTP Protocol Interceptors