servlet-filters

How to use a Servlet Filter to change/rewrite an incoming URL?

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Implement javax.servlet.Filter. In doFilter() method, cast the incoming ServletRequest to HttpServletRequest. Use HttpServletRequest#getRequestURI() to grab the path. Use straightforward java.lang.String methods like substring(), split(), concat() and so on to extract the part of interest and compose the new path. Use either ServletRequest#getRequestDispatcher() and then RequestDispatcher#forward() to forward the request/response to the new URL (server-side redirect, … Read more

How to add filters to servlet without modifying web.xml

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Just do the same job as the container already does. I.e. reinvent the wheel of the chain of responsibility design pattern as is under the covers been used by servlet filters. public class GodFilter implements Filter { private Map<Pattern, Filter> filters = new LinkedHashMap<Pattern, Filter>(); @Override public void init(FilterConfig config) throws ServletException { Filter1 filter1 … Read more

Looking for an example for inserting content into the response using a servlet filter

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The codebase I am using, calls the getOutputStream method, instead of getWriter when it processes the response, so the examples included in the other answer doesn’t help. Here is a more complete answer that works with both the OutputStream and the PrintWriter, even erroring correctly, if the writer is accessed twice. This is derived from … Read more

How do delete a HTTP response header?

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You can’t delete headers afterwards by the standard Servlet API. Your best bet is to just prevent the header from being set. You can do this by creating a Filter which replaces the ServletResponse with a custom HttpServletResponseWrapper implementation which skips the setHeader()‘s job whenever the header name is Content-Disposition. Basically: @Override public void doFilter(ServletRequest … Read more

ContentCachingResponseWrapper Produces Empty Response

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After couple of hours of struggling, I’ve finally found the solution. In short, ContentCachingResponseWrapper.copyBodyToResponse() should be called in the end of the filter method. ContentCachingResponseWrapper caches the response body by reading it from response output stream. So, the stream becomes empty. To write response back to the output stream ContentCachingResponseWrapper.copyBodyToResponse() should be used.

Servlet Filter: How to get all the headers from servletRequest?

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Typecast ServletRequest into HttpServletRequest (only if ServletRequest request is an instanceof HttpServletRequest). Then you can use HttpServletRequest.getHeader() and HttpServletRequest.getHeaderNames() method. Something like this: @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { HttpServletRequest httpRequest = (HttpServletRequest) request; Enumeration<String> headerNames = httpRequest.getHeaderNames(); if (headerNames != null) { while (headerNames.hasMoreElements()) { System.out.println(“Header: ” … Read more

java.lang.IllegalStateException: getReader() has already been called for this request

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Looks like the restlet framework has called getRequestEntityStream() on the Request object which in turn calls getInputStream(), so calling getReader() on the request throws IllegalStateException. The Servlet API documentation for getReader() and getInputStream() says: public java.io.BufferedReader getReader() … … Throws: java.lang.IllegalStateException – if getInputStream() method has been called on this request public ServletInputStream getInputStream() … … Read more

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