Using the FutureRequestExecutionService Based on classic (blocking) I/O handle a great number of concurrent connections is more important than performance in terms of a raw data throughput

Chapter 7. Advanced topics http://hc.apache.org/httpcomponents-client-ga/tutorial/html/advanced.html

7.3. Using the FutureRequestExecutionService

Using the FutureRequestExecutionService, you can schedule http calls and treat the response as a Future. This is useful when e.g. making multiple calls to a web service. The advantage of using the FutureRequestExecutionService is that you can use multiple threads to schedule requests concurrently, set timeouts on the tasks, or cancel them when a response is no longer necessary.

FutureRequestExecutionService wraps the request with a HttpRequestFutureTask, which extends FutureTask. This class allows you to cancel the task as well as keep track of various metrics such as request duration.

7.3.1. Creating the FutureRequestExecutionService

The constructor for the futureRequestExecutionService takes any existing httpClient instance and an ExecutorService instance. When configuring both, it is important to align the maximum number of connections with the number of threads you are going to use. When there are more threads than connections, the connections may start timing out because there are no available connections. When there are more connections than threads, the futureRequestExecutionService will not use all of them

HttpClient httpClient = HttpClientBuilder.create().setMaxConnPerRoute(5).build();
ExecutorService executorService = Executors.newFixedThreadPool(5);
FutureRequestExecutionService futureRequestExecutionService =
    new FutureRequestExecutionService(httpClient, executorService);

7.3.2. Scheduling requests

To schedule a request, simply provide a HttpUriRequest, HttpContext, and a ResponseHandler. Because the request is processed by the executor service, a ResponseHandler is mandatory.

private final class OkidokiHandler implements ResponseHandler<Boolean> {
    public Boolean handleResponse(
            final HttpResponse response) throws ClientProtocolException, IOException {
        return response.getStatusLine().getStatusCode() == 200;
    }
}

HttpRequestFutureTask<Boolean> task = futureRequestExecutionService.execute(
    new HttpGet("http://www.google.com"), HttpClientContext.create(),
    new OkidokiHandler());
// blocks until the request complete and then returns true if you can connect to Google
boolean ok=task.get();

7.3.3. Canceling tasks

Scheduled tasks may be cancelled. If the task is not yet executing but merely queued for execution, it simply will never execute. If it is executing and the mayInterruptIfRunning parameter is set to true, abort() will be called on the request; otherwise the response will simply be ignored but the request will be allowed to complete normally. Any subsequent calls to task.get() will fail with an IllegalStateException. It should be noticed that canceling tasks merely frees up the client side resources. The request may actually be handled normally on the server side.

task.cancel(true)
task.get() // throws an Exception

7.3.4. Callbacks

Instead of manually calling task.get(), you can also use a FutureCallback instance that gets callbacks when the request completes. This is the same interface as is used in HttpAsyncClient

private final class MyCallback implements FutureCallback<Boolean> {

    public void failed(final Exception ex) {
        // do something
    }

    public void completed(final Boolean result) {
        // do something
    }

    public void cancelled() {
        // do something
    }
}

HttpRequestFutureTask<Boolean> task = futureRequestExecutionService.execute(
    new HttpGet("http://www.google.com"), HttpClientContext.create(),
    new OkidokiHandler(), new MyCallback());

7.3.5. Metrics

FutureRequestExecutionService is typically used in applications that make large amounts of web service calls. To facilitate e.g. monitoring or configuration tuning, the FutureRequestExecutionService keeps track of several metrics.

Each HttpRequestFutureTask provides methods to get the time the task was scheduled, started, and ended. Additionally, request and task duration are available as well. These metrics are aggregated in the FutureRequestExecutionService in a FutureRequestExecutionMetrics instance that may be accessed through FutureRequestExecutionService.metrics().

task.scheduledTime() // returns the timestamp the task was scheduled
task.startedTime() // returns the timestamp when the task was started
task.endedTime() // returns the timestamp when the task was done executing
task.requestDuration // returns the duration of the http request
task.taskDuration // returns the duration of the task from the moment it was scheduled

FutureRequestExecutionMetrics metrics = futureRequestExecutionService.metrics()
metrics.getActiveConnectionCount() // currently active connections
metrics.getScheduledConnectionCount(); // currently scheduled connections
metrics.getSuccessfulConnectionCount(); // total number of successful requests
metrics.getSuccessfulConnectionAverageDuration(); // average request duration
metrics.getFailedConnectionCount(); // total number of failed tasks
metrics.getFailedConnectionAverageDuration(); // average duration of failed tasks
metrics.getTaskCount(); // total number of tasks scheduled
metrics.getRequestCount(); // total number of requests
metrics.getRequestAverageDuration(); // average request duration
metrics.getTaskAverageDuration(); // average task duration

Preface http://hc.apache.org/httpcomponents-client-ga/tutorial/html/preface.html

The Hyper-Text Transfer Protocol (HTTP) is perhaps the most significant protocol used on the Internet today. Web services, network-enabled appliances and the growth of network computing continue to expand the role of the HTTP protocol beyond user-driven web browsers, while increasing the number of applications that require HTTP support.

Although the java.net package provides basic functionality for accessing resources via HTTP, it doesn't provide the full flexibility or functionality needed by many applications. HttpClient seeks to fill this void by providing an efficient, up-to-date, and feature-rich package implementing the client side of the most recent HTTP standards and recommendations.

Designed for extension while providing robust support for the base HTTP protocol, HttpClient may be of interest to anyone building HTTP-aware client applications such as web browsers, web service clients, or systems that leverage or extend the HTTP protocol for distributed communication.

1. HttpClient scope

• Client-side HTTP transport library based on HttpCore

• Based on classic (blocking) I/O

• Content agnostic

2. What HttpClient is NOT

• HttpClient is NOT a browser. It is a client side HTTP transport library. HttpClient's purpose is to transmit and receive HTTP messages. HttpClient will not attempt to process content, execute javascript embedded in HTML pages, try to guess content type, if not explicitly set, or reformat request / rewrite location URIs, or other functionality unrelated to the HTTP transport.

Apache HttpComponents – HttpComponents HttpAsyncClient Examples http://hc.apache.org/httpcomponents-asyncclient-dev/examples.html

http://hc.apache.org/httpcomponents-asyncclient-dev/httpasyncclient/examples/org/apache/http/examples/nio/client/AsyncClientHttpExchange.java http://hc.apache.org/httpcomponents-asyncclient-dev/httpasyncclient/examples/org/apache/http/examples/nio/client/AsyncClientHttpExchange.java

package org.apache.http.examples.nio.client;

import java.util.concurrent.Future;

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.nio.client.CloseableHttpAsyncClient;
import org.apache.http.impl.nio.client.HttpAsyncClients;

/**
 * This example demonstrates a basic asynchronous HTTP request / response exchange.
 * Response content is buffered in memory for simplicity.
 */
public class AsyncClientHttpExchange {

    public static void main(final String[] args) throws Exception {
        CloseableHttpAsyncClient httpclient = HttpAsyncClients.createDefault();
        try {
            httpclient.start();
            HttpGet request = new HttpGet("http://httpbin.org/get");
            Future<HttpResponse> future = httpclient.execute(request, null);
            HttpResponse response = future.get();
            System.out.println("Response: " + response.getStatusLine());
            System.out.println("Shutting down");
        } finally {
            httpclient.close();
        }
        System.out.println("Done");
    }

}

Apache HttpComponents – Apache HttpComponents http://hc.apache.org/

HttpComponents AsyncClient

Asynch HttpClient is a HTTP/1.1 compliant HTTP agent implementation based on HttpCore NIO and HttpClient components. It is a complementary module to Apache HttpClient intended for special cases where ability to handle a great number of concurrent connections is more important than performance in terms of a raw data throughput.

• HttpAsyncClient Samples

【nio与性能的关系】