记录一次Required request body is missing的问题排查

接口请求一切正常，但是会报错Required request body is missing的错误。

百般查询和debug后都未查到问题，最后还是在stackOverFlow中找解决方案：

https://stackoverflow.com/questions/35549040/failed-to-read-http-message-org-springframework-http-converter-httpmessagenotre

原因是：我新增了一个Filter用于打印请求和返回日志，部分代码如下：

@OverridepublicvoiddoFilter(ServletRequestrequest,ServletResponseresponse,FilterChainchain)throwsIOException,ServletException{this.preHandle(request,(HttpServletResponse)response);chain.doFilter(request,response);this.afterCompletion((HttpServletRequest)request,(HttpServletResponse)response);}privatevoidpreHandle(HttpServletRequestrequest,HttpServletResponseresponse){try{RequestWrapperrequestWrapper=newRequestWrapper((HttpServletRequest)request);log.info("requestparams：{}",JSON.toJSON(requestWrapper.getBody()));}catch(Exceptione){log.info("logerrorignore",e);}}

@Slf4jpublicclassRequestWrapperextendsHttpServletRequestWrapper{privatefinalStringbody;publicRequestWrapper(HttpServletRequestrequest){super(request);StringBuilderstringBuilder=newStringBuilder();BufferedReaderbufferedReader=null;InputStreaminputStream=null;try{inputStream=request.getInputStream();if(inputStream!=null){bufferedReader=newBufferedReader(newInputStreamReader(inputStream));char[]charBuffer=newchar[128];intbytesRead=-1;while((bytesRead=bufferedReader.read(charBuffer))>0){stringBuilder.append(charBuffer,0,bytesRead);}}else{stringBuilder.append("");}}catch(IOExceptionex){}finally{if(inputStream!=null){try{inputStream.close();}catch(IOExceptione){log.error("inputStreamcloseerror",e);}}if(bufferedReader!=null){try{bufferedReader.close();}catch(IOExceptione){log.error("bufferedReadercloseerror",e);}}}body=stringBuilder.toString();}@OverridepublicServletInputStreamgetInputStream()throwsIOException{finalByteArrayInputStreambyteArrayInputStream=newByteArrayInputStream(body.getBytes());ServletInputStreamservletInputStream=newServletInputStream(){@OverridepublicbooleanisFinished(){returnfalse;}@OverridepublicbooleanisReady(){returnfalse;}@OverridepublicvoidsetReadListener(ReadListenerreadListener){}@Overridepublicintread()throwsIOException{returnbyteArrayInputStream.read();}};returnservletInputStream;}@OverridepublicBufferedReadergetReader()throwsIOException{returnnewBufferedReader(newInputStreamReader(this.getInputStream()));}publicStringgetBody(){returnthis.body;}}

开始总是找不到原因，最后是上述链接里的一番话，才让我恍然大悟，找到根源，见下图：

inputstream只可以读取一次！看到这句话，基本问题就迎刃而解了。最简单的方式就是在filter里不要读取inputstream，当然如果你想读取的话，可以采用下面的方式，思路也是上图中说的：decorate the httpServletRequest。代码如下：

@OverridepublicvoiddoFilter(ServletRequestrequest,ServletResponseresponse,FilterChainchain)throwsIOException,ServletException{RequestWrapperrequestWrapper=newRequestWrapper((HttpServletRequest)request);this.preHandle(requestWrapper,(HttpServletResponse)response);//此处传封装后的HttpServletRequestchain.doFilter(requestWrapper,response);this.afterCompletion((HttpServletRequest)request,(HttpServletResponse)response);}

RequestWrapper不用改，封装HttpServletRequest之后，doFilter也传入封装的HttpServletRequest即可。

总结

一. 为什么inputStream只可以读取一次

InputStream read方法内部会记录position，用于记录当前流读取到的位置，若已读完，read方法会返回-1，(经常和inputStream打交道的，应该都会while(read() != -1) ，用这种方式读取inputStream)。若读取完再次读取的话可以调用inputStream.reset方法，此方法的前提是此方法markSupported返回true。HttpServletRequest使用的是ServletInputStream，看源码可知ServletInputStream没有实现reset和markSupported方法，那么ServletInputStream无法reset之后再次读取，所以inputStream只可以读取一次！ （我要是对基础有深刻的了解，就不会查这么久了。）

publicsynchronizedvoidreset()throwsIOException{thrownewIOException("mark/resetnotsupported");}/***Testsifthisinputstreamsupportsthe<code>mark</code>and*<code>reset</code>methods.Whetherornot<code>mark</code>and*<code>reset</code>aresupportedisaninvariantpropertyofa*particularinputstreaminstance.The<code>markSupported</code>method*of<code>InputStream</code>returns<code>false</code>.**@return<code>true</code>ifthisstreaminstancesupportsthemark*andresetmethods;<code>false</code>otherwise.*@seejava.io.InputStream#mark(int)*@seejava.io.InputStream#reset()*/publicbooleanmarkSupported(){returnfalse;}

二. StackOverFlow真靠谱，有问题先上StackOverFlow