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));

public static String getParameters(HttpServletRequest request){
        String params = request.getQueryString();
        if (StringUtils.isNotBlank(params)) {
            return params;
        }
        try {
            StringBuilder stringBuilder = new StringBuilder();
            BufferedReader streamReader = new BufferedReader(new InputStreamReader(request.getInputStream(), "UTF-8"));
            String inputStr;
            while ((inputStr = streamReader.readLine()) != null) {
                stringBuilder.append(inputStr);
            }
            return stringBuilder.toString();
        } catch (Exception e) {
            return null;
        }
    }

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。

@Slf4j
public class RepeatedlyReadRequestWrapper extends HttpServletRequestWrapper {

    private final byte[] body;

    private static final int BUFFER_START_POSITION = 0;

    private static final int CHAR_BUFFER_LENGTH = 1024;

    public RepeatedlyReadRequestWrapper(HttpServletRequest request) throws IOException
    {
        super(request);
        StringBuilder stringBuilder = new StringBuilder();

        InputStream inputStream = null;
        try {
            inputStream = request.getInputStream();
        } catch (IOException e) {
            log.error("Error reading the request body…", e);
        }
        if (inputStream != null) {
            try (BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream))) {
                char[] charBuffer = new char[CHAR_BUFFER_LENGTH];
                int bytesRead;
                while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {
                    stringBuilder.append(charBuffer, BUFFER_START_POSITION, bytesRead);
                }
            } catch (IOException e) {
                log.error("Fail to read input stream",e);
            }
        } else {
            stringBuilder.append("");
        }
        body = stringBuilder.toString().getBytes();
    }

    @Override
    public BufferedReader getReader() throws IOException
    {
        return new BufferedReader(new InputStreamReader(getInputStream()));
    }

    @Override
    public ServletInputStream getInputStream() throws IOException
    {
        final ByteArrayInputStream bais = new ByteArrayInputStream(body);

        return new ServletInputStream(){

            @Override
            public boolean isFinished()
            {
                return false;
            }

            @Override
            public boolean isReady()
            {
                return false;
            }

            @Override
            public void setReadListener(ReadListener listener)
            {

            }

            @Override
            public int read() throws IOException
            {
                return bais.read();
            }

        };

    }

    @Override
    public String getHeader(String name)
    {
        return super.getHeader(name);
    }

    @Override
    public Enumeration<String> getHeaderNames()
    {
        return super.getHeaderNames();
    }

    @Override
    public Enumeration<String> getHeaders(String name)
    {
        return super.getHeaders(name);
    }
}

2、将包装后的HttpServletRequest传递到后面的请求链路中。

@Component
@WebFilter
public class RepeatlyReadFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        if (request instanceof HttpServletRequest) {
            request = new RepeatedlyReadRequestWrapper((HttpServletRequest) request);
        }
        chain.doFilter(request, response);
    }
}

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：