场景：前端在request body中传了多个参数，为了方便使用@RequestBody映射成相应的参数对象。

@PostMapping(value = "/game/sync")public WebMessage gameMsgReport(UserInfo userInfo,@RequestBody GameMsg msgJson){ gameService.gameMsgReport(userInfo.getUserId(), msgJson); return WebMessage.DEFAULT;}　　　

问题：部署到测试后对象参数始终是空的，传的参数无法映射。

原因分析：@RequestBody 原理上就是spring在进行请求转发时，通过InputStream读取Request body中的数据，然后分装成指定的对象类型参数。所以怀疑问题出在数据读取上，经过资料查询发现HttpServletRequest的数据流只能被读取一次，读取后就不能再重置。所以排查项目拦截器中使用到Request的InputStream的地方，果然发现：在日志输出时使用InputStream读取了Request中的数据

accessLogger.debug("user access,requestURI = {},headers = {},params = {}",request.getRequestURI(),ServletUtils.getHeaderInfo(request),ServletUtils.getParameters(request));

 1 public static String getParameters(HttpServletRequest request){ 2 String params = request.getQueryString(); 3 if (StringUtils.isNotBlank(params)) { 4 return params; 5  } 6 try { 7 StringBuilder stringBuilder = new StringBuilder(); 8 BufferedReader streamReader = new BufferedReader(new InputStreamReader(request.getInputStream(), "UTF-8")); 9  String inputStr;10 while ((inputStr = streamReader.readLine()) != null) {11  stringBuilder.append(inputStr);12  }13 return stringBuilder.toString();14 } catch (Exception e) {15 return null;16  }17 }

解决方法：将Request中的数据读取后缓存下来。

1、继承HttpServletRequestWrapper，将Request请求中的数据读取完缓存到封装类中。

 1 @Slf4j 2 public class RepeatedlyReadRequestWrapper extends HttpServletRequestWrapper { 3  4 private final byte[] body; 5  6 private static final int BUFFER_START_POSITION = 0; 7  8 private static final int CHAR_BUFFER_LENGTH = 1024; 9 10 public RepeatedlyReadRequestWrapper(HttpServletRequest request) throws IOException11  {12 super(request);13 StringBuilder stringBuilder = new StringBuilder();14 15 InputStream inputStream = null;16 try {17 inputStream = request.getInputStream();18 } catch (IOException e) {19 log.error("Error reading the request body…", e);20  }21 if (inputStream != null) {22 try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream))) {23 char[] charBuffer = new char[CHAR_BUFFER_LENGTH];24 int bytesRead;25 while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {26  stringBuilder.append(charBuffer, BUFFER_START_POSITION, bytesRead);27  }28 } catch (IOException e) {29 log.error("Fail to read input stream",e);30  }31 } else {32 stringBuilder.append("");33  }34 body = stringBuilder.toString().getBytes();35  }36 37  @Override38 public BufferedReader getReader() throws IOException39  {40 return new BufferedReader(new InputStreamReader(getInputStream()));41  }42 43  @Override44 public ServletInputStream getInputStream() throws IOException45  {46 final ByteArrayInputStream bais = new ByteArrayInputStream(body);47 48 return new ServletInputStream(){49 50  @Override51 public boolean isFinished()52  {53 return false;54  }55 56  @Override57 public boolean isReady()58  {59 return false;60  }61 62  @Override63 public void setReadListener(ReadListener listener)64  {65 66  }67 68  @Override69 public int read() throws IOException70  {71 return bais.read();72  }73 74  };75 76  }77 78  @Override79 public String getHeader(String name)80  {81 return super.getHeader(name);82  }83 84  @Override85 public Enumeration<String> getHeaderNames()86  {87 return super.getHeaderNames();88  }89 90  @Override91 public Enumeration<String> getHeaders(String name)92  {93 return super.getHeaders(name);94  }95 }

2、将包装后的HttpServletRequest传递到后面的请求链路中。

 1 @Component 2 @WebFilter 3 public class RepeatlyReadFilter implements Filter { 4  5  @Override 6 public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { 7 if (request instanceof HttpServletRequest) { 8 request = new RepeatedlyReadRequestWrapper((HttpServletRequest) request); 9  }10  chain.doFilter(request, response);11  }12 }

还有一个知识点：因为第一次读取Request中的数据是在拦截器Interceptor中，而缓存Request中的数据是在过滤器Filter中做的，所以就涉及到两者的执行顺讯问题。Filter依赖于Servlet容器，基于函数回调；Interceptor依赖于web框架（如SpringMVC），基于java反射，两者并没有什么关系，而Filter的执行在Interceptor之前，盗用网上一张执行流程图，如下：