How Can I Read HTTP POST Request Parameters Multiple Times Without Consuming Them?

Http Servlet Request Parameters Disappearing in Post Body

Problem:

In a Java Servlet filter, attempting to access multiple HTTP request parameters retrieved from a POST request body results in the second parameter being unavailable. This occurs because consuming the parameters consumes them for the entire request.

Question:

Is there a way to read the request parameters without consuming them?

Answer:

Alternative Solution:

Using aspects to create a custom interceptor component can be an alternative solution, enabling multiple reads without involving the filter chain and offering improved efficiency.

Extended HttpServletRequestWrapper Solution:

To preserve request body parameters for multiple reads in a filter chain, extend the HttpServletRequestWrapper class and employ an input stream cache:

public class MultiReadHttpServletRequest extends HttpServletRequestWrapper {
  private ByteArrayOutputStream cachedBytes;

  public MultiReadHttpServletRequest(HttpServletRequest request) {
    super(request);
  }

  @Override
  public ServletInputStream getInputStream() throws IOException {
    if (cachedBytes == null) cacheInputStream();

    return new CachedServletInputStream(cachedBytes.toByteArray());
  }

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

  private void cacheInputStream() throws IOException {
    cachedBytes = new ByteArrayOutputStream();
    IOUtils.copy(super.getInputStream(), cachedBytes);
  }

  // CachedServletInputStream implementation omitted for brevity
}

Filter Usage:

Wrap the original request in the extended class before passing it through the filter chain:

public class MyFilter implements Filter {
  @Override
  public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
    MultiReadHttpServletRequest multiReadRequest = new MultiReadHttpServletRequest((HttpServletRequest) request);

    // Perform multiple reads here

    chain.doFilter(multiReadRequest, response);
  }
}

This approach enables multiple reads via getInputStream(), getReader(), and parameter retrieval methods.

Update for Newer ServletInputStream:

Implement additional methods isReady(), setReadListener(), and isFinished() in the cached stream implementation to adhere to the updated ServletInputStream interface.

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