Lazily Check the Body of an HttpServletResponse

LazyResponseBodyChecker.java

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletOutputStream;
import javax.servlet.WriteListener;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;

public class LazyResponseBodyChecker extends HttpServletResponseWrapper {

	public LazyResponseBodyChecker(final HttpServletResponse response) {
		super(response);
	}

	@Override
	public ServletOutputStream getOutputStream() throws IOException {
		final ServletOutputStream superStream = super.getOutputStream();

		return new ServletOutputStream() {

			@Override
		    public void write(final byte buf[]) throws IOException {
				// All other methods eventually call this one, so
				// just examine the buffer here.
				final String string = new String(buf);

				final byte newBuf[] = string.getBytes();

		        write(newBuf, 0, newBuf.length);
		    }

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

			@Override
			public void setWriteListener(final WriteListener listener) {
				superStream.setWriteListener(listener);

			}

			@Override
			public void write(final int b) throws IOException {
				superStream.write(b);
			}

		};
	}

	@Override
	public PrintWriter getWriter() throws IOException {
		return new PrintWriter(super.getWriter()) {

			@Override
			public void write(final char[] buf, final int off, final int len) {
				final String string = new String(buf);

				// examine or modify the string here

				super.write(string.toCharArray(), off, len);
			}

		};
	}
}

I used this code in my blog post Lazily Check the Body of an HttpServletResponse.