再聊HttpClient的NoHttpResponseException

序

本文主要研究一下抛出NoHttpResponseException的调用链

异常堆栈

HttpRequestExecutor.execute

org/apache/http/protocol/HttpRequestExecutor.java

doSendRequest返回null，则执行doReceiveResponse，这里会抛出NoHttpResponseException

doReceiveResponse

org/apache/http/protocol/HttpRequestExecutor.java

这里conn.receiveResponseHeader()会抛出NoHttpResponseException

receiveResponseHeader

org/apache/http/impl/DefaultBHttpClientConnection.java

DefaultBHttpClientConnection的receiveResponseHeader方法在执行responseParser.parse()的时候会抛出NoHttpResponseException

parse

org/apache/http/impl/io/AbstractMessageParser.java

AbstractMessageParser的parse方法执行parseHead会抛出NoHttpResponseException

parseHead

org/apache/http/impl/conn/DefaultHttpResponseParser.java

DefaultHttpResponseParser的parseHead在通过sessionBuffer.readLine(this.lineBuf)读取为-1且count=0时抛出NoHttpResponseException

doSendRequest

org/apache/http/protocol/HttpRequestExecutor.java

doSendRequest在request的header指定需要expect且是http1.1的时候才会通过conn.receiveResponseHeader()去接收response，否则response会返回null；这里先conn.sendRequestHeader(request)，针对post等执行conn.sendRequestEntity，接着flush把等待发送的数据发送出去

小结

HttpRequestExecutor.execute方法，doSendRequest返回null，则执行doReceiveResponse，这里会抛出NoHttpResponseException；doSendRequest先执行conn.sendRequestHeader(request)，针对post等执行conn.sendRequestEntity，接着flush把等待发送的数据发送出去，针对需要expect且是http1.1的这里的response才可能有值。

单纯从HttpRequestExecutor.execute代码上看抛出NoHttpResponseException时，不法断定服务端是否接收到请求

doc

• 聊聊HttpClient的NoHttpResponseException
• Expect