Check available connections in PoolingClientConnectionManager - httpclient

Question

Is there a way (and how) to know the status of a connection pool? Like, how many connections are being used, how many are available, ...
We are currently facing issues where the application cannot get a connection from the pool (ConnectionPoolTimeoutException: Timeout waiting for connection from pool) so to track down the cause we would like to log some pool stats each time a new connection is requested.
I have been browsing the Apache HTTPClient API but did not find a way to get this information.
We use PoolingClientConnectionManager.

Answer 1

You can use methods of the ConnPoolControl interface to control parameters of the internal pool

Answer 2

You can have a detailed information total and per route with the code below:
public static void main(String[] args) {
PoolingHttpClientConnectionManager connectionManager = HttpClientUtils.getConnectionManager();
System.out.println(createHttpInfo(connectionManager));
}
private static String createHttpInfo(PoolingHttpClientConnectionManager connectionManager) {
StringBuilder sb = new StringBuilder();
sb.append("=========================").append("\n");
sb.append("General Info:").append("\n");
sb.append("-------------------------").append("\n");
sb.append("MaxTotal: ").append(connectionManager.getMaxTotal()).append("\n");
sb.append("DefaultMaxPerRoute: ").append(connectionManager.getDefaultMaxPerRoute()).append("\n");
sb.append("ValidateAfterInactivity: ").append(connectionManager.getValidateAfterInactivity()).append("\n");
sb.append("=========================").append("\n");
PoolStats totalStats = connectionManager.getTotalStats();
sb.append(createPoolStatsInfo("Total Stats", totalStats));
Set<HttpRoute> routes = connectionManager.getRoutes();
if (routes != null) {
for (HttpRoute route : routes) {
sb.append(createRouteInfo(connectionManager, route));
}
}
return sb.toString();
}
private static String createRouteInfo(PoolingHttpClientConnectionManager connectionManager, HttpRoute route) {
PoolStats routeStats = connectionManager.getStats(route);
String info = createPoolStatsInfo(route.getTargetHost().toURI(), routeStats);
return info;
}
private static String createPoolStatsInfo(String title, PoolStats poolStats) {
StringBuilder sb = new StringBuilder();
sb.append(title + ":").append("\n");
sb.append("-------------------------").append("\n");
if (poolStats != null) {
sb.append("Available: ").append(poolStats.getAvailable()).append("\n");
sb.append("Leased: ").append(poolStats.getLeased()).append("\n");
sb.append("Max: ").append(poolStats.getMax()).append("\n");
sb.append("Pending: ").append(poolStats.getPending()).append("\n");
}
sb.append("=========================").append("\n");
return sb.toString();
}
Update (2019-01-07)
The connection manager is retrieved from an utilitarian class I've created (you can create it differently):
public class HttpClientUtils {
private static final PoolingHttpClientConnectionManager connectionManager = createConnectionManager();
private static PoolingHttpClientConnectionManager createConnectionManager() {
try {
SSLConnectionSocketFactory socketFactory = new SSLConnectionSocketFactory(
SSLContext.getDefault(),
new String[] {"TLSv1", "TLSv1.1", "TLSv1.2"},
null,
SSLConnectionSocketFactory.getDefaultHostnameVerifier());
Registry<ConnectionSocketFactory> registry = RegistryBuilder.<ConnectionSocketFactory>create()
.register("http", PlainConnectionSocketFactory.INSTANCE)
.register("https", socketFactory)
.build();
PoolingHttpClientConnectionManager cm = new PoolingHttpClientConnectionManager(registry);
cm.setMaxTotal(200);
cm.setDefaultMaxPerRoute(20);
return cm;
} catch (NoSuchAlgorithmException | RuntimeException ex) {
Logger.getLogger(HttpClientUtils.class.getName()).log(Level.SEVERE, null, ex);
return null;
}
}
public static PoolingHttpClientConnectionManager getConnectionManager() {
return connectionManager;
}
}