使用httpclient必须知道的参数设置及代码写法、存在的风险

org.apache.http.conn.ConnectionPoolTimeoutException:  Timeout  waiting  for  connection  from  pool
at org. apache. http. impl. conn. PoolingClientConnectionManager. leaseConnection( PoolingClientConnectionManager. java: 232)
at org. apache. http. impl. conn. PoolingClientConnectionManager$ 1. getConnection( PoolingClientConnectionManager. java: 199)
at  org. apache. http. impl. client. DefaultRequestDirector. execute( DefaultRequestDirector. java: 456)

另外通过jstack查看线程，会发现：

“pool-21-thread-3″ prio=10 tid=0x00007f6b7c002800 nid=0x40ff waiting on condition [0x00007f6b37020000]
java.lang.Thread.State: TIMED_WAITING (parking)
at sun.misc.Unsafe.park(Native Method)
- parking to wait for <0x00000000f97918b8> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
at java.util.concurrent.locks.LockSupport.parkUntil(LockSupport.java:239)
at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.awaitUntil(AbstractQueuedSynchronizer.java:2072)
at org.apache.http.pool.PoolEntryFuture.await(PoolEntryFuture.java:129)
at org.apache.http.pool.AbstractConnPool.getPoolEntryBlocking(AbstractConnPool.java:281)
at org.apache.http.pool.AbstractConnPool.access$000(AbstractConnPool.java:62)
at org.apache.http.pool.AbstractConnPool$2.getPoolEntry(AbstractConnPool.java:176)
at org.apache.http.pool.AbstractConnPool$2.getPoolEntry(AbstractConnPool.java:172)
at org.apache.http.pool.PoolEntryFuture.get(PoolEntryFuture.java:100)
at org.apache.http.impl.conn.PoolingClientConnectionManager.leaseConnection(PoolingClientConnectionManager.java:212)

问题：

因为使用了连接池，但连接不够用，造成大量的等待；而且这种等待都有滚雪球的效应（和交易组最近使用的apache common dbcp存在的风险是类似的）。

解决方案

最终我们定了一些合理的参数值，目前来看还没有遇到问题。

思考

其实出问题的原因是我们对一些参数不了解，随意设置其值，不出现问题则好，出现问题很难排查到原因，因此我把使用httpclient必须设置的参数及代码写法及排查方法总结一下，供参考。

参数设置

1、httpclient 4.2.3

2、httpclient 3.1

参数类似 就不多解释了；

代码写法

1、

httpclient 4.2.3
HttpResponse response = null;
HttpEntity entity = null;
try {
  HttpGet get = new HttpGet();
  String url = "http://hc.apache.org/";
  get.setURI(new URI(url));
  response = getHttpClient().execute(get);
/  /处理响应
} catch (Exception e) {
  //处理异常
} finally {
  if(response != null) { 
    EntityUtils.consume(response.getEntity()); //会自动释放连接
  }
  //如下方法也是可以的，但是存在一些风险；不要用
  //InputStream is = response.getEntity().getContent();
  //is.close();
}

2、

httpclient 3.1
PostMethod postMethod = new PostMethod(yxUrl);
try { 
  httpClient.executeMethod(postMethod);
} catch (Exception e) {
  //处理异常
} finally {
  if(postMethod != null) { //不要忘记释放，尽量通过该方法实现，
    postMethod.releaseConnection();
    //存在风险，不要用
    //postMethod.setParameter("Connection", "close");
    //InputStream is = postMethod.getResponseBodyAsStream();
    //is.clsoe();也会关闭并释放连接的
  }
}

存在的风险

1、httpclient 4.2.3 在释放连接时

if (managedConn.isOpen() && !managedConn.isMarkedReusable()) { //如果连接打开的且不可重用（not keepalive） close socket
  try {
    managedConn.shutdown();
  } catch (IOException iox) {
    if (this.log.isDebugEnabled()) {
      this.log.debug("I/O exception shutting down released connection", iox);
    }
  }
}
// Only reusable connections can be kept alive
if (managedConn.isMarkedReusable()) {
  entry.updateExpiry(keepalive, tunit != null ? tunit : TimeUnit.MILLISECONDS);
  if (this.log.isDebugEnabled()) {
    String s;
    if (keepalive > 0) {
      s = "for " + keepalive + " " + tunit;
    } else { 
      s = "indefinitely";
    }
    this.log.debug("Connection " + format(entry) + " can be kept alive " + s);
  }
}

2、httpclient 3.1

其他注意事项：

如有问题，请赐教。