Java Http连接池中的连接收回策略

Question

I am trying to implement a http connection pooling in java for a web service. The service will receive a request and then call other http services.

public final class HttpClientPool {
 private static HttpClientPool instance = null;
 private PoolingHttpClientConnectionManager manager;
 private IdleConnectionMonitorThread monitorThread;
 private final CloseableHttpClient client;

 public static HttpClientPool getInstance() {
  if (instance == null) {
   synchronized(HttpClientPool.class) {
    if (instance == null) {
     instance = new HttpClientPool();
    }
   }
  }
  return instance;
 }

 private HttpClientPool() {
  manager = new PoolingHttpClientConnectionManager();
  client = HttpClients.custom().setConnectionManager(manager).build();
  monitorThread = new IdleConnectionMonitorThread(manager);
  monitorThread.setDaemon(true);
  monitorThread.start();
 }

 public CloseableHttpClient getClient() {
  return client;
 }
}


class IdleConnectionMonitorThread extends Thread {
 private final HttpClientConnectionManager connMgr;
 private volatile boolean shutdown;

 IdleConnectionMonitorThread(HttpClientConnectionManager connMgr) {
  super();
  this.connMgr = connMgr;
 }

 @Override
 public void run() {
  try {
   while (!shutdown) {
    synchronized(this) {
     wait(5000);
     // Close expired connections
     connMgr.closeExpiredConnections();
     // Optionally, close connections
     // that have been idle longer than 30 sec
     connMgr.closeIdleConnections(60, TimeUnit.SECONDS);
    }
   }
  } catch (InterruptedException ex) {
   //
  }
 }

 void shutdown() {
  shutdown = true;
  synchronized(this) {
   notifyAll();
  }
 }
}

1. As mentioned in Connection Management doc for Connection Eviction strategy instead of using a IdleConnectionMonitorThread what if I use manager.setValidateAfterInactivity . What are the pros & cons of the above two approach?

2. Is the above Http Connection Pool implementation correct?

Answer 1

With #setValidateAfterInactivity set to a positive value persistent connections will get validated upon lease request. That is, stale and non-reusable connections will not get automatically evicted from the pool until an attempt is made to re-use them.

Running a dedicated thread that iterates over persistent connections at the specified time interval and removes expired or idle connections from the pool ensures proactive connection eviction at the cost of an extra thread and slightly higher pool lock contention.

Answer 2

In HttpClient 4.5.3, manager.setValidateAfterInactivity has a defult value of 2000 which is 2 seconds. So I would suggest not to use a IdleConnectionMonitorThread unless you want the application to validate inactive connections and clean up at the same time.