HTTP长连接与短连接使用方法及测试详解

客户端设置的有效期大于服务端的，那么实际连接的有效期呢？三分钟之后再次请求，从连接池中lease连接的时候，提示Connection expired @ Wed Apr 26 14:08:05，即在上一次请求之后的5s失效，说明是服务端的设置生效了。

[2017-04-26 14:11:00 DEBUG] (org.apache.http.impl.conn.PoolingHttpClientConnectionManager:?) - Connection request: [route: {}->http://bizdomain:80][total kept alive: 1; route allocated: 1 of 32; total allocated: 1 of 200]

[2017-04-26 14:11:00 DEBUG] (org.apache.http.impl.conn.CPool:?) - Connection [id:2][route:{}->http://bizdomain:80][state:null] expired @ Wed Apr 26 14:08:05 GMT+08:00 2017

源码分析

通过源代码了解一下连接失效时间的设置过程。

//org.apache.http.impl.execchain.MainClientExec#execute
......
//从连接池中lease connection
final HttpClientConnectionmanagedConn = connRequest.get(timeout > 0 ? timeout : 0, TimeUnit.MILLISECONDS);
......
//将conenction封装在ConnectionHolder中
final ConnectionHolder connHolder = new ConnectionHolder(this.log, this.connManager, managedConn);
......
// The connection is in or can be brought to a re-usable state.
//如果返回值消息头中connection设置为close，则返回false
if (reuseStrategy.keepAlive(response, context)) {
  // Set the idle duration of this connection
  //取出response消息头中，keep-alive的timeout值
  final long duration = keepAliveStrategy.getKeepAliveDuration(response, context);
  if (this.log.isDebugEnabled()) {
    final String s;
    if (duration > 0) {
      s = "for " + duration + " " + TimeUnit.MILLISECONDS;
    } else {
      s = "indefinitely";
    }
    this.log.debug("Connection can be kept alive " + s);
  }
  //设置失效时间
  connHolder.setValidFor(duration, TimeUnit.MILLISECONDS);
  connHolder.markReusable();
} else {
  connHolder.markNonReusable();
}

待读取响应之后，释放连接，即：connHolder.releaseConnection()。调用org.apache.http.impl.conn.PoolingHttpClientConnectionManager#releaseConnection方法。

  @Override
  public void releaseConnection(final HttpClientConnection managedConn, 
      final Object state,final long keepalive, final TimeUnit tunit) {
    Args.notNull(managedConn, "Managed connection");
    synchronized (managedConn) {
      final CPoolEntry entry = CPoolProxy.detach(managedConn);
      if (entry == null) {
        return;
      }
      final ManagedHttpClientConnection conn = entry.getConnection();
      try {
        if (conn.isOpen()) {
          final TimeUnit effectiveUnit = tunit != null ? tunit : TimeUnit.MILLISECONDS;
          entry.setState(state);
          //设置失效时间
          entry.updateExpiry(keepalive, effectiveUnit);
        }
      } finally {
      。。。。。。
        }
      }
    }
  }

然后再下一次HTTP操作，从连接池中获取连接时

//org.apache.http.impl.conn.PoolingHttpClientConnectionManager#requestConnection调用org.apache.http.pool.AbstractConnPool#lease，
//调用getPoolEntryBlocking,调用org.apache.http.impl.conn.CPoolEntry#isExpired
@Override
public boolean isExpired(final long now) {
  final boolean expired = super.isExpired(now);
  if (expired && this.log.isDebugEnabled()) {
  //日志中看到的内容
    this.log.debug("Connection " + this + " expired @ " + new Date(getExpiry()));
  }
  return expired;
}
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