How to set a parameter in a HttpServletRequest

Question

I am using a javax servlet http HttpServletRequest to implement a web application   I have no problem to get the parameter of a request using the getParameter method  However I don t know how to set a parameter in my request

User · Accepted Answer

You can t  not using the standard API  HttpServletRequest represent a request received by the server  and so adding new parameters is not a valid option  as far as the API is concerned    You could in principle implement a subclass of HttpServletRequestWrapper which wraps the original request  and intercepts the getParameter   methods  and pass the wrapped request on when you forward   If you go this route  you should use a Filter to replace your HttpServletRequest with a HttpServletRequestWrapper   public void doFilter ServletRequest servletRequest  ServletResponse servletResponse  FilterChain filterChain  throws IOException  ServletException       if  servletRequest instanceof HttpServletRequest            HttpServletRequest request    HttpServletRequest  servletRequest             Check wether the current request needs to be able to support the body to be read multiple times         if  MULTI READ HTTP METHODS contains request getMethod                      Override current HttpServletRequest with custom implementation             filterChain doFilter new HttpServletRequestWrapper request   servletResponse               return                      filterChain doFilter servletRequest  servletResponse

User · Answer

From your question  I think what you are trying to do is to store something  an object  a string     to foward it then to another servlet  using RequestDispatcher    To do this you don t need to set a paramater but an attribute using  void setAttribute String name  Object o     and then  Object getAttribute String name

User · Answer

If you really want to do this  create an HttpServletRequestWrapper   public class AddableHttpRequest extends HttpServletRequestWrapper       private HashMap params   new HashMap        public AddableingHttpRequest HttpServletRequest request               super request            public String getParameter String name                  if we added one  return that one            if   params get  name      null                      return params get  name                               otherwise return what s in the original request            HttpServletRequest req    HttpServletRequest  super getRequest               return validate  name  req getParameter  name               public void addParameter  String name  String value                params put  name  value

User · Answer

The most upvoted solution generally works but for Spring and or Spring Boot  the values will not wire to parameters in controller methods annotated with  RequestParam unless you specifically implemented getParameterValues    I combined the solution s  here and from this blog  import java util    import javax servlet http HttpServletRequest  import javax servlet http HttpServletRequestWrapper   public class MutableHttpRequest extends HttpServletRequestWrapper        private final Map lt String  String   gt  mutableParams   new HashMap lt  gt          public MutableHttpRequest final HttpServletRequest request            super request              public MutableHttpRequest addParameter String name  String value            if  value    null              mutableParams put name  new String     value              return this              Override     public String getParameter final String name            String   values   getParameterMap   get name            return Arrays stream values                   findFirst                    orElse super getParameter name                Override     public Map lt String  String   gt  getParameterMap             Map lt String  String   gt  allParameters   new HashMap lt  gt             allParameters putAll super getParameterMap             allParameters putAll mutableParams            return Collections unmodifiableMap allParameters               Override     public Enumeration lt String gt  getParameterNames             return Collections enumeration getParameterMap   keySet                 Override     public String   getParameterValues final String name            return getParameterMap   get name             note that this code is not super-optimized but it works

User · Answer

The missing getParameterMap override ended up being a real problem for me  So this is what I ended up with   import java util HashMap  import java util Map   import javax servlet http HttpServletRequest  import javax servlet http HttpServletRequestWrapper           Request wrapper enabling the update of a request-parameter          author E K  de Lang        final class HttpServletRequestReplaceParameterWrapper     extends HttpServletRequestWrapper        private final Map lt String  String   gt  keyValues        SuppressWarnings  unchecked       HttpServletRequestReplaceParameterWrapper HttpServletRequest request  String key  String value                super request            keyValues   new HashMap lt String  String   gt             keyValues putAll request getParameterMap                Can override the values in the request         keyValues put key  new String     value                  SuppressWarnings  unchecked       HttpServletRequestReplaceParameterWrapper HttpServletRequest request  Map lt String  String gt  additionalRequestParameters                super request           keyValues   new HashMap lt String  String   gt             keyValues putAll request getParameterMap             for  Map Entry lt String  String gt  entry   additionalRequestParameters entrySet                  keyValues put entry getKey    new String     entry getValue                              Override     public String getParameter String name                if  keyValues containsKey name                 String   strings   keyValues get name               if  strings    null    strings length    0                    return null                            else                   return strings 0                                   else                  Just in case the request has some tricks of it s own              return super getParameter name                         Override     public String   getParameterValues String name                String   value   this keyValues get name           if  value    null                   Just in case the request has some tricks of it s own              return super getParameterValues name                     else               return value                        Override     public Map lt String  String   gt  getParameterMap                 return this keyValues

User · Answer

As mentioned in the previous posts  using an HttpServletReqiestWrapper is the way to go  however the missed part in those posts was that apart from overriding the method getParameter    you should also override other parameter related methods to produce a consistent response  e g  the value of a param added by the custom request wrapper should also be included in the parameters map returned by the method getParameterMap    Here is an example      public class AddableHttpRequest extends HttpServletRequestWrapper            A map containing additional request params this wrapper adds to the wrapped request        private final Map lt String  String gt  params   new HashMap lt  gt                     Constructs a request object wrapping the given request          throws java lang IllegalArgumentException if the request is null             AddableHttpRequest final HttpServletRequest request            super request              Override     public String getParameter final String name               if we added one with the given name  return that one         if   params get  name      null                 return params get  name              else                  otherwise return what s in the original request             return super getParameter name                                        OVERRIDE THE METHODS BELOW TO REFLECT PARAMETERS ADDED BY THIS WRAPPER                    Override     public Map lt String  String gt  getParameterMap                defaulf impl  should be overridden for an approprivate map of request params         return super getParameterMap                Override     public Enumeration lt String gt  getParameterNames                defaulf impl  should be overridden for an approprivate map of request params names         return super getParameterNames                Override     public String   getParameterValues final String name               defaulf impl  should be overridden for an approprivate map of request params values         return super getParameterValues name

User · Answer

Sorry  but why not use the following construction   request getParameterMap   put parameterName  new String    parameterValue

[java] How to set a parameter in a HttpServletRequest?

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