Suppose I have two Spring webapps deployed to the same Tomcat server instance:
A:
ROOT.war, context = /
#Controller
class TestController {
#RequestMapping("/api/someMethod")
public String someMethod() {
//..
}
#RequestMapping("/api/v1/someMethod")
public String someMethod() {
//..
}
}
B:
api#v1.war, context = /api/v1/
#Controller
class TestController {
#RequestMapping("/someMethod")
public String someMethod() {
//..
}
}
Which web application will be used to process the following HTTP requests?
GET http://<hostname>/api/someMethod
GET http://<hostname>/api/v1/someMethod
GET http://<hostname>/api/v1/nonexistentMethod
As you can see the second HTTP request matches both apps. I have tried to find answer in Tomcat docs, but found none. Where is specified how context path matching works?
According to Servlet 3.0 Specification
10.1 Web Applications Within Web Servers
A Web application is rooted at a specific path within a Web server.
For example, a catalog application could be located at
http://www.mycorp.com/catalog. All requests that start with this
prefix will be routed to the ServletContext which represents the
catalog application.
A servlet container can establish rules for
automatic generation of Web applications. For example a ~user/
mapping could be used to map to a Web application based at
/home/user/public_html/
12.1 Use of URL Paths
Upon receipt of a client request, the Web container determines the
Web application to which to forward it. The Web application selected
must have the longest context path that matches the start of the
request URL. The matched part of the URL is the context path when
mapping to servlets. The Web container next must locate the servlet
to process the request using the path mapping procedure described
below. The path used for mapping to a servlet is the request URL from
the request object minus the context path and the path parameters.
The URL path mapping rules below are used in order. The first
successful match is used with no further matches attempted:
The container will try to find an exact match of the path of the request to the path of the servlet. A successful match selects the
servlet.
The container will recursively try to ma tch the longest path-pre fix. This is done by stepping down the path tree a directory at a
time, using the ’ / ’ character as a path separator. The longest
match determines the servlet selected.
If the last segment in the URL path contains an extension (e.g. .jsp ), the servlet container will try to match a servlet that
handles requests for the extension. An extension is defined as the
part of the last segment after the last ’ . ’ character.
Versions of this specification prior to 2.5 made use of these mapping techniques as a suggestion rather than a requirement,
allowing servlet containers to each have their different schemes for
mapping client requests to servlets.
If neither of the previous three rules re sult in a servlet match, the container will attempt to serve content appropriate for the
resource requested. If a "default" servlet is defined for the
application, it will be used. Many containers provide an implicit
default servlet for serving content.
Also Tomcat Request Process Flow might be useful
Related
My Servlet show product details by slug
#WebServlet("/*")
public class ProductDetails extends HttpServlet {
for example :
mywebsite.com/product-name
But they can't load css, js and img files because it detect the pathInfo for a slug.
How can I exclude them to not be loaded in the servlet?
Unfortunately the Servlet spec does not define exclusion rules for URL pattern mappings. Also, matched paths take precedence over matched suffixes (see Servlet 4 spec, paragraphs 12.1 & 12.2). The mapping on this Servlet will match anything in the application's context path, including static resources.
What can you do:
You can split the logic to handle static resources in that servlet. I would not go for it, it will probably complicate the code and hurt the separation of concerns.
If your static resources are inside a specific directory and no slug will match it (e.g. all JS, CSS, HTML, image files under assets/), you can have another Servlet that serves the static content under this directory (e.g. #WebServlet("/assets/*")). The longest path mapping that matches the request takes precedence. You still need to write code for sending a file back to the client; this code is fairly easy, you get a chance to customize the headers of the static files (e.g. caching), and, in comparison to the previous solution, the code that handles static files lies in it's own Servlet, so nice separation of concerns.
If you do not want to bother with serving static files yourself (I wouldn't blame you), you can move the logic from your Servlet to another class. Then introduce a Servlet filter that will first check if the request is a GET for a static resource and, if so, simply calls filterChain.doFilter(request,response) and lets the application server handle the static file. If not, it calls your logic and sends the response that your Servlet would have sent.
Finally, if you make your Servlet the default Servlet by #WebServlet("/") (not "/*"). It will pick up any request that other Servlets do not. The application server should have a Servlet installed for static content that will serve any existing CSS, JS, etc files from your application. Anything else will end up in your default Servlet.
If you could find a way to separate static content from dynamic content, e.g. all static content under assets/, all dynamic content under the virtual path content/ it would be much easier to change the mapping of your Servlet to /content/* and be done with it.
I am running a Jetty web server and I have a generic servlet filter to handle exceptions. As part of this, I want to log aggregated metrics about which servlets are causing the exceptions. Is there a way I can figure out which servlets defined in the web.xml match the servlet path of the current request?
I have a generic servlet filter to handle exceptions
I take you to mean that your filter extends javax.servlet.GenericFilter directly.
Is there a way I can figure out which servlets defined in the web.xml match the servlet path of the current request?
In any given servlet context there should not be more than one servlet mapped to a given servlet path, so in any given case you're looking for just one servlet, not multiple.
As far as I know or can tell, GenericFilter and the generic ServletRequests and ServletResponses with which it works do not provide a good way to access the information you are after. If you cast the request to HttpServletRequest, however, then you can obtain its HttpServletMapping (since Servlet 4.0 / Java EE 8)
, which contains the servlet name as declared in the webapp's deployment descriptor, among other information. Or the HttpServletRequest can directly provide the servlet path, too.
But if you are contemplating casting the requests, then you would probably be better off having your filter extend javax.servlet.http.HttpFilter, which would give you type-safe access. This is itself a subclass of GenericFilter, so it probably wouldn't be difficult to perform such a refactoring.
The familiar code:
<servlet-mapping>
<servlet-name>main</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>main</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
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?
<url-pattern>/*</url-pattern>
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().
<url-pattern>/</url-pattern>
The / doesn't override any other servlet. It only replaces the servletcontainer's built in 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 built in 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 built in JSP servlet will be invoked, which is already by default mapped on the more specific URL pattern *.jsp.
<url-pattern></url-pattern>
Then there's also the empty string URL pattern . This will be invoked when the context root is requested. This is different from the <welcome-file> 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 "home page servlet". 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 built in 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?
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.
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:
<servlet-mapping>
<servlet-name>viewServlet</servlet-name>
<url-pattern>/perfix/*</url-pattern>
</servlet-mapping>
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.
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).
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.
I was looking at a tutorial on Spring MVC, and noticed that the dispatcher servlet is mapped to the urlpattern /and it was explained that this means that all requests will be handled by the servlet defined to handle that urlpattern.
That makes sense, but I thought that /* was the notation used to specify all requests, not just /. What is the difference between a url pattern of / and one of /*? I would think that / would map to the context path of the application. so for example, if 'myapp' was the context root of the app:
myipaddress/myapp would be handled by a urlpattern of /
myipaddress/myapp/foo would be handled by a urlpattern of /*
Can someone help me understand where I'm going wrong
The url-pattern specification:
A string beginning with a ‘/’ character and ending with a ‘/*’ suffix
is used for path mapping.
A string beginning with a ‘*.’ prefix is used as an extension mapping.
A string containing only the ’/’ character indicates the "default"
servlet of the application. In this case the servlet path is the
request URI minus the context path and the path info is null.
All other strings are used for exact matches only.
http://download.oracle.com/otndocs/jcp/servlet-3.0-fr-eval-oth-JSpec/
Is it permissible to have multiple entries as the context root of a servlet?
For instance, all Sun examples use a single /catalog or something similar as the context root, but could it be /catalog/furniture as well?
The Servlet 2.4 Specification is not specific here.
Context Path: The path prefix associated with the ServletContext that this servlet is a part of. If this context is the “default”
context rooted at the base of the Web server’s URL name space, this
path will be an empty string. Otherwise, if the context is not rooted
at the root of the server’s name space, the path starts with a’/’
character but does not end with a’/’ character.
WE can't give multiple context root to a servlet. But we can change dynamically with different names in server.xml as
<web-uri>Project.war</web-uri>
<context-root>myproj</context-root>
We can configure our project context root with different names but it should be one name.
By default if you call contextPath using request object as req.getContextPath(); it will get by default with slash(/) as /myproj.
For more info to change context roots as static to dynamic you can check here.
Yes. It's just a prefix. It must start with "/", and cannot end with "/" unless it is "/". Interior slashes are allowed.
E.g. all Sun examples use a single "/catalog" or similar as the context root, but can it be
"/catalog/furniture" as well?
In your web.xml, are you suggesting that you'd map "catalog/" and "catalog/furniture/" to the same servlet? What would be the point? I think the servlet engine will route both of these requests to the same servlet.
If you're suggesting that you've got two WAR files, one named catalog.war and another named something else, and both need to route all requests to the same servlet, either you'll have to have the .class file for that servlet in both WAR files, or the root servlet for the something else context will have to be written so it redirects all requests to the catalog.war root servlet.
Can you be a bit clearer as to what exactly you have in mind? I think what you'd like to accomplish is a little confusing.
No. You can't have slash in context root path.
However, you can achieve the same effect with context root as "/catalog". Just put all your static and JSP files under "/furniture" in the WAR and add map the Servlets accordingly.