Java Request Wrapper for Logging | Generated by AI

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In Java web applications, you typically use a HttpServletRequestWrapper when you want to decorate or modify the behavior of the standard HttpServletRequest without touching the servlet container’s implementation.

How HttpServletRequestWrapper works

• It’s a decorator around the original HttpServletRequest.
• You subclass HttpServletRequestWrapper and override methods such as getInputStream(), getReader(), or getParameter().
• This is useful when you want to read or cache the request body (which by default can only be read once) or modify/query request parameters.

Why you need it for logging

• By default, the servlet request body (InputStream) can be consumed only once. If you log it directly in a filter, the controller won’t be able to read it afterward.
• Wrapping allows you to cache the body so it can be read multiple times: once for logging, once for downstream processing.
• URL parameters can be logged by accessing request.getParameterMap() or request.getQueryString().

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Example: Logging body and URL params

Here’s a filter using a custom wrapper:

public class CachedBodyHttpServletRequest extends HttpServletRequestWrapper {
    private byte[] cachedBody;

    public CachedBodyHttpServletRequest(HttpServletRequest request) throws IOException {
        super(request);
        InputStream requestInputStream = request.getInputStream();
        this.cachedBody = requestInputStream.readAllBytes();
    }

    @Override
    public ServletInputStream getInputStream() {
        ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(this.cachedBody);
        return new ServletInputStream() {
            @Override
            public int read() {
                return byteArrayInputStream.read();
            }
            @Override
            public boolean isFinished() {
                return byteArrayInputStream.available() == 0;
            }
            @Override
            public boolean isReady() {
                return true;
            }
            @Override
            public void setReadListener(ReadListener readListener) {}
        };
    }

    @Override
    public BufferedReader getReader() {
        return new BufferedReader(new InputStreamReader(this.getInputStream()));
    }

    public String getBody() {
        return new String(this.cachedBody, StandardCharsets.UTF_8);
    }
}

Then use it in a filter:

@WebFilter("/*")
public class LoggingFilter implements Filter {
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {

        CachedBodyHttpServletRequest wrappedRequest = new CachedBodyHttpServletRequest((HttpServletRequest) request);

        // Log URL
        String url = wrappedRequest.getRequestURL().toString();
        String query = wrappedRequest.getQueryString();

        // Log params
        Map<String, String[]> params = wrappedRequest.getParameterMap();

        // Log body
        String body = wrappedRequest.getBody();

        System.out.println("Request URL: " + url + (query != null ? "?" + query : ""));
        System.out.println("Parameters: " + params);
        System.out.println("Body: " + body);

        // Continue filter chain
        chain.doFilter(wrappedRequest, response);
    }
}

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Key Points

• HttpServletRequestWrapper lets you safely read the body multiple times.
• For URL parameters: getParameterMap() or getQueryString() is enough.
• Be cautious with large bodies (you may want streaming or size limits).
• In production, use a logging framework (SLF4J + Logback/Log4J2) instead of System.out.

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Do you want me to also show you a Spring Boot–style solution (using OncePerRequestFilter and ContentCachingRequestWrapper), since that’s much simpler?

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