HttpRequest中InputStream只能一次性读取问题采坑
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 IOException 11 { 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 @Override 38 public BufferedReader getReader() throws IOException 39 { 40 return new BufferedReader(new InputStreamReader(getInputStream())); 41 } 42 43 @Override 44 public ServletInputStream getInputStream() throws IOException 45 { 46 final ByteArrayInputStream bais = new ByteArrayInputStream(body); 47 48 return new ServletInputStream(){ 49 50 @Override 51 public boolean isFinished() 52 { 53 return false; 54 } 55 56 @Override 57 public boolean isReady() 58 { 59 return false; 60 } 61 62 @Override 63 public void setReadListener(ReadListener listener) 64 { 65 66 } 67 68 @Override 69 public int read() throws IOException 70 { 71 return bais.read(); 72 } 73 74 }; 75 76 } 77 78 @Override 79 public String getHeader(String name) 80 { 81 return super.getHeader(name); 82 } 83 84 @Override 85 public Enumeration<String> getHeaderNames() 86 { 87 return super.getHeaderNames(); 88 } 89 90 @Override 91 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：
