问题描述

在使用 CloseableHttpClient 调用一个URL的时候，底层抛出以下异常信息：

Caused by: org.apache.http.ProtocolException: The server failed to respond with a valid HTTP response at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:151) ~[httpclient-4.5.2.jar:4.5.2] at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:57) ~[httpclient-4.5.2.jar:4.5.2] at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:261) ~[httpcore-4.4.4.jar:4.4.4] at org.apache.http.impl.DefaultBHttpClientConnection.receiveResponseHeader(DefaultBHttpClientConnection.java:165) ~[httpcore-4.4.4.jar:4.4.4] at org.apache.http.impl.conn.CPoolProxy.receiveResponseHeader(CPoolProxy.java:167) ~[httpclient-4.5.2.jar:4.5.2] at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:272) ~[httpcore-4.4.4.jar:4.4.4] at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:124) ~[httpcore-4.4.4.jar:4.4.4] at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:271) ~[httpclient-4.5.2.jar:4.5.2] at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:184) ~[httpclient-4.5.2.jar:4.5.2] at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:88) ~[httpclient-4.5.2.jar:4.5.2] at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110) ~[httpclient-4.5.2.jar:4.5.2] at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184) ~[httpclient-4.5.2.jar:4.5.2] ... 47 common frames omitted

追踪定位

尝试百度后，普遍认为是 HttpClient异常/被占用 的问题。团队讨论分析后认为不然，转战 StackOverflow ，最后判断是调用的URL所在的服务器返回不正确的响应消息，导致DefaultHttpResponseParser解析失败。调整传入的URL后，问题解决。

结语

问题的定位需要细心，不要盲目相信和轻易下结论。