How to Enable Multiple Reads of POST Request Body in Java Servlet Filters?
Nov 28, 2024 pm 03:21 PMMultiple Reads of Post Request Body in Java Servlet Filters
Problem:
In Java Servlet filters, accessing HTTP request parameters from a POST request body can result in the parameters being unavailable later in the filter chain. This occurs because the request body is consumed during the initial read.
Solution:
To overcome this issue and enable multiple reads of the request body parameters, a solution involves extending HttpServletRequestWrapper and caching the input stream bytes. Here's a custom request wrapper class:
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); } /* An input stream which reads the cached request body */ private static class CachedServletInputStream extends ServletInputStream { private final ByteArrayInputStream buffer; public CachedServletInputStream(byte[] contents) { this.buffer = new ByteArrayInputStream(contents); } @Override public int read() { return buffer.read(); } @Override public boolean isFinished() { return buffer.available() == 0; } @Override public boolean isReady() { return true; } @Override public void setReadListener(ReadListener listener) { throw new RuntimeException("Not implemented"); } } }
Usage:
Wrap the original request with the custom wrapper 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); doMyThing(multiReadRequest.getInputStream()); chain.doFilter(multiReadRequest, response); } }
This allows for multiple reads of the request body, either through the getInputStream() or getReader() methods.
Note:
For newer versions of the ServletInputStream interface, additional methods like isReady() and setReadListener() need to be implemented in the custom input stream class. Refer to the link provided in the answer for details.
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