Difference between and in servlet mapping url pattern

Question

The familiar code     lt servlet-mapping gt       lt servlet-name gt main lt  servlet-name gt       lt url-pattern gt    lt  url-pattern gt   lt  servlet-mapping gt    lt servlet-mapping gt       lt servlet-name gt main lt  servlet-name gt       lt url-pattern gt   lt  url-pattern gt   lt  servlet-mapping gt    My understanding is that    maps to http   host port context     How about    It sure doesn t map to http   host port context root only  In fact  it will accept http   host port context hello  but reject http   host port context hello jsp   Can anyone explain how is http   host port context hello mapped

User · Answer

I d like to supplement BalusC s answer with the mapping rules and an example   Mapping rules from Servlet 2 5 specification    Map exact URL Map wildcard paths Map extensions Map to the default servlet   In our example  there re three servlets     is the default servlet installed by us   Tomcat installs two servlets to serve jsp and jspx   So to map http   host port context hello   No exact URL servlets installed  next  No wildcard paths servlets installed  next  Doesn t match any extensions  next  Map to the default servlet  return    To map http   host port context hello jsp   No exact URL servlets installed  next  No wildcard paths servlets installed  next  Found extension servlet  return

User · Answer

The essential difference between    and   is that a servlet with mapping    will be selected before any servlet with an extension mapping  like   html   while a servlet with mapping   will be selected only after extension mappings are considered  and will be used for any request which doesn t match anything else---it is the  default servlet     In particular  a    mapping will always be selected before a   mapping   Having either prevents any requests from reaching the container s own default servlet   Either will be selected only after servlet mappings which are exact matches  like  foo bar  and those which are path mappings longer than     like  foo      Note that the empty string mapping is an exact match for the context root  http   host port context     See Chapter 12 of the Java Servlet Specification  available in version 3 1 at http   download oracle com otndocs jcp servlet-3 1-fr-eval-spec index html

User · Answer

I think Candy s answer is mostly correct  There is one small part I think otherwise   To map host port context hello jsp   No exact URL servlets installed  next  Found wildcard paths servlets  return    I believe that why      does not match host port context hello because it treats   hello  as a path instead of a file  since it does not have an extension

User · Answer

lt url-pattern gt    lt  url-pattern gt  The    on a servlet overrides all other servlets  including all servlets provided by the servletcontainer such as the default servlet and the JSP servlet  Whatever request you fire  it will end up in that servlet  This is thus a bad URL pattern for servlets  Usually  you d like to use    on a Filter only  It is able to let the request continue to any of the servlets listening on a more specific URL pattern by calling FilterChain doFilter     lt url-pattern gt   lt  url-pattern gt  The   doesn t override any other servlet  It only replaces the servletcontainer s builtin default servlet for all requests which doesn t match any other registered servlet  This is normally only invoked on static resources  CSS JS image etc  and directory listings  The servletcontainer s builtin default servlet is also capable of dealing with HTTP cache requests  media  audio video  streaming and file download resumes  Usually  you don t want to override the default servlet as you would otherwise have to take care of all its tasks  which is not exactly trivial  JSF utility library OmniFaces has an open source example   This is thus also a bad URL pattern for servlets  As to why JSP pages doesn t hit this servlet  it s because the servletcontainer s builtin JSP servlet will be invoked  which is already by default mapped on the more specific URL pattern   jsp   lt url-pattern gt  lt  url-pattern gt  Then there s also the empty string URL pattern    This will be invoked when the context root is requested  This is different from the  lt welcome-file gt  approach that it isn t invoked when any subfolder is requested  This is most likely the URL pattern you re actually looking for in case you want a  quot home page servlet quot   I only have to admit that I d intuitively expect the empty string URL pattern   and the slash URL pattern   be defined exactly the other way round  so I can understand that a lot of starters got confused on this  But it is what it is  Front Controller In case you actually intend to have a front controller servlet  then you d best map it on a more specific URL pattern like   html    do   pages     app    etc  You can hide away the front controller URL pattern and cover static resources on a common URL pattern like  resources     static    etc with help of a servlet filter  See also How to prevent static resources from being handled by front controller servlet which is mapped on     Noted should be that Spring MVC has a builtin static resource servlet  so that s why you could map its front controller on   if you configure a common URL pattern for static resources in Spring  See also How to handle static content in Spring MVC

User · Answer

Perhaps you need to know how urls are mapped too  since I suffered 404 for hours  There are two kinds of handlers handling requests  BeanNameUrlHandlerMapping and SimpleUrlHandlerMapping  When we defined a servlet-mapping  we are using SimpleUrlHandlerMapping  One thing we need to know is these two handlers share a common property called alwaysUseFullPath which defaults to false    false here means Spring will not use the full path to mapp a url to a controller  What does it mean  It means when you define a servlet-mapping    lt servlet-mapping gt       lt servlet-name gt viewServlet lt  servlet-name gt       lt url-pattern gt  perfix   lt  url-pattern gt   lt  servlet-mapping gt    the handler will actually use the   part to find the controller  For example  the following controller will face a 404 error when you request it using  perfix api feature doSomething   Controller    RequestMapping   perfix api feature   public class MyController        RequestMapping value     doSomething   method   RequestMethod GET        ResponseBody     public String doSomething HttpServletRequest request                           It is a perfect match  right  But why 404  As mentioned before  default value of alwaysUseFullPath is false  which means in your request  only  api feature doSomething is used to find a corresponding Controller  but there is no Controller cares about that path  You need to either change your url to  perfix perfix api feature doSomething or remove perfix from MyController base  RequestingMapping

[servlets] Difference between / and /* in servlet mapping url pattern

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