TeeFilter registered like this:

 
@Bean public FilterRegistrationBean<TeeFilter> requestResponseFilter2() {
    FilterRegistrationBean<TeeFilter> filterRegBean = new FilterRegistrationBean<>();
    filterRegBean.setFilter(new TeeFilter());
    filterRegBean.setName("Logback access-logging request response filter");
    return filterRegBean;
}

Symptom

Webapp fails to process multipart HTTP requests with the following exception:

org.springframework.web.multipart.MultipartException: Failed to parse multipart servlet request; nested exception is java.io.IOException: org.apache.tomcat.util.http.fileupload.FileUploadException: Stream closed

Troubleshooting

• Multipart requests work when TeeFilter is disabled.
• Multipart requests work when Spring Boot is downgraded to 2.1.12 (Tomcat still 9.0.30, Logback still 1.2.3)

Root cause
`TeeFilter` decorates incoming request with `TeeHttpServletRequest` that reads the input stream and closes it (see `TeeServletInputStream#duplicateInputStream`). Everything works as expected here.

However, when `HttpServletRequest#getParts` is called later, `TeeHttpServletRequest` delegates it to the original request, which has its stream closed already, which results in the exception.

Workaround

Force loading of parts before request passes through `TeeFilter`. With Tomcat this is as simple as:

private static class MultipartSafeTeeFilter extends TeeFilter {
   @Override
   public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
        request.getParameter("whatever");
        super.doFilter(request, response, filterChain);
  }
}