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Web Component Certification (OCEJWCD)

Compression Filter

Adolfo Eloy

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posted 11 years ago

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Hi all.

I'm studying chapter 13 from HF Servlets and JSP and I'm trouble with the Compression Filter example.
I've written all the code for this example (regarding the Errata for HF Servlets And JSP).

When requesting the most pages (either via servlet's URL pattern or directly JSP) I got no problems.
But when I try to call a specific Servlet all I get on the browser is a blank page.

This is the code of my Servlet:

Did anybody here already see this kind of problem?
Any ideas?

Thanks in advance.

Adolfo Eloy
Software Developer
OCPJP 6

Frits Walraven

Creator of Enthuware JWS+ V6

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posted 11 years ago

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Hi Adolfo,

Did you try adding the HTML codes in your Servlet, like this:
If that doesn't work, please post your web.xml and the URL you are using to access the Servlet.

Regards,
Frits

Adolfo Eloy

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posted 11 years ago

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Hi Frits. Thanks for replying. I've tried what you post, but no success...
Instead of posting my web.xml, I've change the code to use Servlet 3.0's annotations to ease this post, ok?

This is a bit modified example of Compression filter available at Head First Servlet & JSP.

My servlet code:

This is the code of the filter:

@WebFilter("/*")
public class CompressorFilter implements Filter {
	private ServletContext ctx;
	private FilterConfig cfg;

public void init(FilterConfig fConfig) throws ServletException {
		this.cfg = fConfig;
		ctx = cfg.getServletContext();
		ctx.log(cfg.getFilterName() + " initialized");
	}
	
	public void destroy() {
		ctx = null;
		cfg = null;
	}

public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
		HttpServletRequest request = (HttpServletRequest) req;
		HttpServletResponse response = (HttpServletResponse) resp;
		
		String validEncodings = request.getHeader("Accept-Encoding");
		if (validEncodings.indexOf("gzip") > -1) {
			CompressionResponseWrapper wrappedResp = new CompressionResponseWrapper(response);
			wrappedResp.setHeader("Content-Encoding", "gzip");
			chain.doFilter(request, wrappedResp);
			GZIPOutputStream gzos = wrappedResp.getGZIPOutputStream();
			gzos.finish();
		} else {
			chain.doFilter(request, response);
		}
		
	}

}

Compression response wrapper:

public class CompressionResponseWrapper extends HttpServletResponseWrapper {
	private GZIPServletOutputStream servletGzipOS = null;
	private PrintWriter pw = null;
	private Object streamUsed = null;
	
	public CompressionResponseWrapper(HttpServletResponse response) {
		super(response);
	}

@Override
	public void setContentLength(int length) { }
	
	public GZIPOutputStream getGZIPOutputStream() {
		return this.servletGzipOS.internalGzipOS;
	}
	
	@Override
	public ServletOutputStream getOutputStream() throws IOException {
		
		if ((streamUsed != null) && (streamUsed == pw)) {
			throw new IllegalStateException();
		}
		
		if (servletGzipOS == null) {
			servletGzipOS = new GZIPServletOutputStream(getResponse().getOutputStream());
			streamUsed = servletGzipOS;
		}
		
		return servletGzipOS;
	}
	
	@Override
	public PrintWriter getWriter() throws IOException {
		
		if ((streamUsed != null) && (streamUsed == servletGzipOS)) {
			throw new IllegalStateException();
		}
		
		if (pw == null) {
			servletGzipOS = new GZIPServletOutputStream(getResponse().getOutputStream());
			OutputStreamWriter osw = new OutputStreamWriter(
				servletGzipOS, getResponse().getCharacterEncoding());
			pw = new PrintWriter(osw);
			streamUsed = pw;
		}
		
		return pw;
	}
}

and gzip servlet output stream wrapper:

Thanks in advance.

Adolfo Eloy
Software Developer
OCPJP 6

Frits Walraven

Creator of Enthuware JWS+ V6

Posts: 3412

320

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posted 11 years ago

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If you uncomment the following line (se debugging tip page 723)
You will see that the browser gets zipped data.

Regards,
Frits