我在使用 apache http client 库发送 http 请求时，遇到了一个奇怪的问题

对于我发送的 http 请求的说明（如果需要其它信息，我随时补充）：

post 请求

Content-Type: application/json

Content-Length: 1277

如果我在发送给请求的时候，加上 Expect: 100-continue 这个 header ，请求就会成功；没有这个 header 请求就失败 SocketTimeoutException ，错误日志：

java.net.SocketTimeoutException : Read timed out
	at java.net.SocketInputStream.socketRead0(Native Method)
 	at java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
 	at java.net.SocketInputStream.read(SocketInputStream.java:171)
 	at java.net.SocketInputStream.read(SocketInputStream.java:141)
 	at org.apache.http.impl.io.SessionInputBufferImpl.streamRead(SessionInputBufferImpl.java:137)
 	at org.apache.http.impl.io.SessionInputBufferImpl.fillBuffer(SessionInputBufferImpl.java:153)
 	at org.apache.http.impl.io.SessionInputBufferImpl.readLine(SessionInputBufferImpl.java:282)
 	at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:138)
 	at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:56)
 	at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:259)
 	at org.apache.http.impl.DefaultBHttpClientConnection.receiveResponseHeader(DefaultBHttpClientConnection.java:163)
 	at org.apache.http.impl.conn.CPoolProxy.receiveResponseHeader(CPoolProxy.java:165)
 	at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:273)
 	at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:125)
 	at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:272)
 	at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:185)
 	at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
 	at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
 	at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
 	at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
 	at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:108)

我重复了很多次，携带 headerExpect: 100-continue就成功，不带就失败（偶尔也会成功）。

实在搞不懂为什么，求教 v 友