Lazily Check the Body of an HttpServletRequest

LazyRequestBodyChecker.java

import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.StringReader;
import java.util.stream.Collectors;

import javax.servlet.ReadListener;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

public class LazyRequestBodyChecker extends HttpServletRequestWrapper {

	public LazyRequestBodyChecker(final HttpServletRequest request) {
		super(request);
	}

	@Override
	public ServletInputStream getInputStream() throws IOException {
		final ServletInputStream inputSteam = super.getInputStream();

		final String string = new String(inputSteam.readAllBytes());

		// Analyze or even modify the string here.

		final InputStream innerStream = new ByteArrayInputStream(string.getBytes());

		return new ServletInputStream() {

			@Override
			public boolean isFinished() {
				return inputSteam.isFinished();
			}

			@Override
			public boolean isReady() {
				return inputSteam.isReady();
			}

			@Override
			public void setReadListener(final ReadListener listener) {
				inputSteam.setReadListener(listener);
			}

			@Override
			public int read() throws IOException {
				return innerStream.read();
			}
		};
	}

	@Override
	public BufferedReader getReader() throws IOException {
		final BufferedReader reader = super.getReader();

		final String string = reader.lines()
				.map(s -> s)       // You could analyze or modify
				.filter(s -> true) // the string in the stream itself
				.collect(Collectors.joining());

		// Or analyze or modify it here afterwards.

		return new BufferedReader(new StringReader(string));
	}
}

LazyRequestBodyCheckerFilter.java

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;

public class LazyRequestBodyCheckerFilter implements Filter {

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

		if (request instanceof HttpServletRequest) {
			final HttpServletRequest httpServletRequest = (HttpServletRequest) request;
			chain.doFilter(new LazyRequestBodyChecker(httpServletRequest), response);
		}
	}
}

web.xml

<filter>
  <filter-name>LazyRequestBodyCheckerFilter</filter-name>
  <display-name>LazyRequestBodyCheckerFilter</display-name>
  <!-- Don't forget to include the fully qualified name if included in a package! -->
  <filter-class>LazyRequestBodyCheckerFilter</filter-class>
</filter>
<filter-mapping>
  <filter-name>LazyRequestBodyCheckerFilter</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>

I reference this code in my blog post Lazily Check the Body of an HttpServletRequest.