getReader() has already been called for this request

상황

2026-01-07T08:09:10.277+09:00 ERROR 5032 --- [nio-8080-exec-3] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed: java.lang.IllegalStateException: getReader() has already been called for this request] with root cause
java.lang.IllegalStateException: getReader() has already been called for this request

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발생 원인

LoggingFilter 에서 request body를 읽은 후 Spring 이 다시 읽으려고 해서 발생하는 오류 

@Slf4j
@Component
public class LoggingFilter implements Filter{

  @Override
  public void doFilter(ServletRequest request, ServletResponse response,
      FilterChain chain) throws IOException, ServletException {

    if(request instanceof HttpServletRequest httpServletRequest){
      String url = httpServletRequest.getRequestURI();
      String method = httpServletRequest.getMethod();
      String body = getRequestBody(httpServletRequest);

      log.info("Incoming Request: URL = {}, Method = {}, Body = {}", url, method, body);
    }

    chain.doFilter(request, response); // 다음 필터 또는 컨트롤러로 요청 전달
  }

  private String getRequestBody(HttpServletRequest request){
    try (BufferedReader reader = request.getReader()) {
      return reader.lines().collect(Collectors.joining(System.lineSeparator()));
    } catch (IOException e){
      log.error("Failed to read request body", e);
      return "Unable to read request body";
    }
  }

}

 

HttpServletRequest의 InputStream/Reader는 한 번만 읽을 수 있다. 

1. LoggingFilter에서 request.getReader()로 body를 읽음

2. chain.doFilter()로 요청 전달

3. Spring이 @RequestBody를 처리하기 위해 다시 body를 읽으려함 

4. 이미 읽은 stream을 다시 읽으려고 해서 IllegalStateException 발생 

 

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해결방안

  ContentCachingRequestWrapper 또는 커스텀 Wrapper를 사용해서 body를 캐싱

 

@Slf4j
@Component
public class LoggingFilter implements Filter {

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
        FilterChain chain) throws IOException, ServletException {

        if (request instanceof HttpServletRequest httpServletRequest) {
            ContentCachingRequestWrapper wrappedRequest = new ContentCachingRequestWrapper(httpServletRequest);

            chain.doFilter(wrappedRequest, response);

            String url = wrappedRequest.getRequestURI();
            String method = wrappedRequest.getMethod();
            String body = new String(wrappedRequest.getContentAsByteArray(), StandardCharsets.UTF_8);

            log.info("Request: URL = {}, Method = {}, Body = {}", url, method, body);
        } else {
            chain.doFilter(request, response);
        }
    }
}

 

  1. ContentCachingRequestWrapper: Spring이 제공하는 래퍼 클래스로, request body를 내부에 캐싱
  2. 로깅 시점 변경: chain.doFilter() 후에 로깅해야 getContentAsByteArray()에 데이터가 채워짐
  3. 래핑된 request 전달: chain.doFilter(wrappedRequest, response)로 래핑된 객체 전달

 

 

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