Multithreaded HTTPClient

Question

public class test { public static final int nThreads = 2; public static void main(String[] args) throws ExecutionException, InterruptedException{ // Runnable myrunnable = new myRunnable(); ExecutorService execute = Executors.newFixedThreadPool(nThreads); for (int i = 0; i < nThreads; ++i) { execute.execute(new MyTask()); } execute.awaitTermination(1000, TimeUnit.MILLISECONDS); execute.shutdown(); } } class MyTask implements Runnable { public static final int maxCalls = 10; public static final int sleepMillis = 500; private static HttpResponse response; private static HttpClient httpclient; public void run(){ int counter = 0; while (true) { if (counter >= maxCalls) { break; } try { Thread.currentThread().sleep(sleepMillis); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } execHttpRequest(); ++counter; } } private void execHttpRequest() { httpclient = new DefaultHttpClient(); HttpGet httpget = new HttpGet("My URL"); try { response = httpclient.execute(httpget); BufferedReader br = new BufferedReader(new InputStreamReader(response.getEntity().getContent())); String output; while((output=br.readLine())!=null){ System.out.println(Thread.currentThread().getName() +output); } br.close(); httpclient.getConnectionManager().shutdown(); //httpclient.getConnectionManager().shutdown(); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally{ httpclient.getConnectionManager().shutdown(); } } } 

When I run this code, I get the following exception:

 Exception in thread "pool-1-thread-1" java.lang.IllegalStateException: Invalid use of SingleClientConnManager: connection still allocated. Make sure to release the connection before allocating another one. at org.apache.http.impl.conn.SingleClientConnManager.getConnection(SingleClientConnManager.java:216) at org.apache.http.impl.conn.SingleClientConnManager$1.getConnection(SingleClientConnManager.java:190) at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:401) at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:820) at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:754) at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:732) at MyTask.execHttpRequest(test.java:72) at MyTask.run(test.java:60) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:722) java.io.InterruptedIOException: Connection has been shut down at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:543) at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:820) at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:754) at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:732) at MyTask.execHttpRequest(test.java:72) at MyTask.run(test.java:60) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603) at java.lang.Thread.run(Thread.java:722) Caused by: org.apache.http.impl.conn.ConnectionShutdownException at org.apache.http.impl.conn.AbstractPooledConnAdapter.assertValid(AbstractPooledConnAdapter.java:86) at org.apache.http.impl.conn.AbstractPooledConnAdapter.getRoute(AbstractPooledConnAdapter.java:112) at org.apache.http.impl.client.DefaultRequestDirector.establishRoute(DefaultRequestDirector.java:740) at org.apache.http.impl.client.DefaultRequestDirector.tryConnect(DefaultRequestDirector.java:577) at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:425) ... 8 more 

When I execute an HTTP request, I see these Exceptions. It works great for single threaded. I am trying to call a specific URL (which works fine), but when I add multiple threads to it, it throws an exception from an illegal state.

Answer 1

I realized my stupidity! httpClient and httpRequest were both static. After I made them unstatic, it works great! The executor service gives me better control over flow control, and I really wanted to use it.

Answer 2

You need to define a multithreaded HttpConnectionManager, for example.

 MultiThreadedHttpConnectionManager connectionManager = new MultiThreadedHttpConnectionManager(); HttpClient client = new HttpClient(connectionManager); 

For more information, you can see http://hc.apache.org/httpclient-3.x/threading.html

Answer 3

Came here to say that MultiThreadedHttpConnectionManager is deprecated. Currently (HttpClient version 4. *) this is the way: http://hc.apache.org/httpcomponents-client-ga/tutorial/html/connmgmt.html#d5e639

 SchemeRegistry schemeRegistry = new SchemeRegistry(); schemeRegistry.register( new Scheme("http", 80, PlainSocketFactory.getSocketFactory())); ClientConnectionManager cm = new PoolingClientConnectionManager(schemeRegistry); HttpClient httpClient = new DefaultHttpClient(cm); 

Answer 4

In addition to bpgergo's answer, the connection manager has been updated again (from version HttpClient> = 4.3), and now you should use PoolingHttpClientConnectionManager . The default restrictions for PoolingHttpClientConnectionManager are a total of 20 connections and 2 per route, but they can be overridden.

 PoolingHttpClientConnectionManager cm=new PoolingHttpClientConnectionManager(); cm.setDefaultMaxPerRoute(40); cm.setMaxTotal(500); CloseableHttpClient client = HttpClients.createMinimal(cm);