当应用服务器提示address already in use 时，可考虑http客户端的连接问题，如下http rfc描述。此时需要设置http header
Connection为close
14.10
Connection
The Connection general-header field allows the sender to specify
options that are desired for that particular connection and MUST NOT
be communicated by proxies over further connections.
The Connection header has the following grammar:
Connection = "Connection" ":" 1#(connection-token)
connection-token = token
HTTP/1.1 proxies MUST parse the Connection header field before a
message is forwarded and, for each connection-token in this field,
remove any header field(s) from the message with the same name as the
connection-token. Connection options are signaled by the presence of
a connection-token in the Connection header field, not by any
corresponding additional header field(s), since the additional header
field may not be sent if there are no parameters associated with that
connection option.
Message headers listed in the Connection header MUST NOT include
end-to-end headers, such as Cache-Control.
HTTP/1.1 defines the "close" connection option for the sender to
signal that the connection will be closed after completion of the
response. For example,
Connection: close
in either the request or the response header fields indicates that
the connection SHOULD NOT be considered `persistent' (section 8.1)
after the current request/response is complete.
HTTP/1.1 applications that do not support persistent connections MUST
include the "close" connection option in every message.
A system receiving an HTTP/1.0 (or lower-version) message that
includes a Connection header MUST, for each connection-token in this
field, remove and ignore any header field(s) from the message with
the same name as the connection-token. This protects against mistaken
forwarding of such header fields by pre-HTTP/1.1 proxies. See section
19.6.2
.