Adding an HTTP Header to the request in a servlet filter

Question

I m integrating with an existing servlet that pulls some properties out of the HTTP header   Basically  I m implementing an interface that doesn t have access to the actual request  it just has access to a map of k- v for the HTTP headers   I need to pass in a request parameter   The plan is to use a servlet filter to go from parameter to header value but of course the HttpServletRequest object doesn t have an addHeader   method   Any ideas

User · Answer

You ll have to use an HttpServletRequestWrapper    public void doFilter final ServletRequest request  final ServletResponse response  final FilterChain chain  throws IOException  ServletException       final HttpServletRequest httpRequest    HttpServletRequest  request      HttpServletRequestWrapper wrapper   new HttpServletRequestWrapper httpRequest             Override         public String getHeader String name                final String value   request getParameter name               if  value    null                    return value                            return super getHeader name                        chain doFilter wrapper  response       Depending on what you want to do you may need to implement other methods of the wrapper like getHeaderNames for instance  Just be aware that this is trusting the client and allowing them to manipulate any HTTP header  You may want to sandbox it and only allow certain header values to be modified this way

User · Answer

Extend HttpServletRequestWrapper  override the header getters to return the parameters as well   public class AddParamsToHeader extends HttpServletRequestWrapper       public AddParamsToHeader HttpServletRequest request            super request              public String getHeader String name            String header   super getHeader name           return  header    null    header   super getParameter name      Note  you can t use getParameterValues   here             public Enumeration getHeaderNames             List lt String gt  names   Collections list super getHeaderNames             names addAll Collections list super getParameterNames              return Collections enumeration names               and wrap the original request with it   chain doFilter new AddParamsToHeader  HttpServletRequest  request   response       That said  I personally find this a bad idea  Rather give it direct access to the parameters or pass the parameters to it

User · Answer

as https   stackoverflow com users 89391 miku pointed out this would be a complete ServletFilter example that uses the code that also works for Jersey to add the remote addr header    package com bitplan smartCRM web   import java io IOException  import java util Collections  import java util Enumeration  import java util HashMap  import java util List  import java util Map   import javax servlet Filter  import javax servlet FilterChain  import javax servlet FilterConfig  import javax servlet ServletException  import javax servlet ServletRequest  import javax servlet ServletResponse  import javax servlet http HttpServletRequest  import javax servlet http HttpServletRequestWrapper               author wf         public class RemoteAddrFilter implements Filter         Override     public void destroy                  Override     public void doFilter ServletRequest request  ServletResponse response              FilterChain chain  throws IOException  ServletException           HttpServletRequest req    HttpServletRequest  request          HeaderMapRequestWrapper requestWrapper   new HeaderMapRequestWrapper req           String remote addr   request getRemoteAddr            requestWrapper addHeader  remote addr   remote addr           chain doFilter requestWrapper  response      Goes to default servlet              Override     public void init FilterConfig filterConfig  throws ServletException                  https   stackoverflow com questions 2811769 adding-an-http-header-to-the-request-in-a-servlet-filter        http   sandeepmore com blog 2010 06 12 modifying-http-headers-using-java         http   bijubnair blogspot de 2008 12 adding-header-information-to-existing html                allow adding additional header entries to a request                 author wf                     public class HeaderMapRequestWrapper extends HttpServletRequestWrapper                          construct a wrapper for this request                         param request                     public HeaderMapRequestWrapper HttpServletRequest request                super request                      private Map lt String  String gt  headerMap   new HashMap lt String  String gt                             add a header with given name and value                         param name             param value                     public void addHeader String name  String value                headerMap put name  value                       Override         public String getHeader String name                String headerValue   super getHeader name               if  headerMap containsKey name                     headerValue   headerMap get name                             return headerValue                                    get the Header names                      Override         public Enumeration lt String gt  getHeaderNames                 List lt String gt  names   Collections list super getHeaderNames                 for  String name   headerMap keySet                      names add name                             return Collections enumeration names                       Override         public Enumeration lt String gt  getHeaders String name                List lt String gt  values   Collections list super getHeaders name                if  headerMap containsKey name                     values add headerMap get name                              return Collections enumeration values                         web xml snippet    lt  --  first filter adds remote addr header -- gt   lt filter gt       lt filter-name gt remoteAddrfilter lt  filter-name gt       lt filter-class gt com bitplan smartCRM web RemoteAddrFilter lt  filter-class gt   lt  filter gt   lt filter-mapping gt       lt filter-name gt remoteAddrfilter lt  filter-name gt       lt url-pattern gt    lt  url-pattern gt   lt  filter-mapping gt

[java] Adding an HTTP Header to the request in a servlet filter

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