Detailed explanation of servlet's url-pattern matching rules

This article introduces the url-pattern matching rules of servlets and shares them with you. The details are as follows:

First, we need to clarify a few confusing rules:

1. The matching rules in the servlet container are neither simple wildcards nor regular expressions, but specific rules. So don't use wildcards or regular expression matching rules to view the url-pattern of a servlet.

2. Starting from Servlet 2.5, a servlet can use multiple url-pattern rules. The <servlet-mapping> tag declares the matching rules corresponding to the servlet, and each <url-pattern> tag represents 1 matching rule;

3. When the servlet container receives a url request initiated by the browser, the container will use the url to subtract the current application's context path and use the remaining string as the servlet mapping. If the url is http://localhost:8080/appDemo/index.html and its application context is appDemo, the container will remove http://localhost:8080/appDemo and use the remaining /index.html part to make the servlet mapping match.

4. The url-pattern mapping matching process has priority

5. And when a servlet matches successfully, the remaining servlets will not be paid attention to.

1. Four matching rules

1 Exact match

The items configured in <url-pattern> must match the url exactly.

 <servlet-mapping> <servlet-name>MyServlet</servlet-name> <url-pattern>/user/users.html</url-pattern> <url-pattern>/index.html</url-pattern> <url-pattern>/user/addUser.action</url-pattern></servlet-mapping>

When entering the following URLs in the browser, they will be matched to the servlet
http://localhost:8080/appDemo/user/users.html
http://localhost:8080/appDemo/index.html
http://localhost:8080/appDemo/user/addUser.action

Notice:

http://localhost:8080/appDemo/user/addUser/ is an illegal url and will not be recognized as http://localhost:8080/appDemo/user/addUser

In addition, the above url can be followed by any query conditions, and will be matched, such as

http://localhost:8080/appDemo/user/addUser?username=Tom&age=23 will be matched to the MyServlet.

2 Path Match

A string that starts with the "/" character and ends with "/*" is used for path matching

 <servlet-mapping> <servlet-name>MyServlet</servlet-name> <url-pattern>/user/*</url-pattern></servlet-mapping>

The path starts with /user/, and the following path can be arbitrary. For example, the following urls will be matched.
http://localhost:8080/appDemo/user/users.html
http://localhost:8080/appDemo/user/addUser.action
http://localhost:8080/appDemo/user/updateUser.actionl

3 extension matching

Strings starting with "*." are used for extension matching

 <servlet-mapping> <servlet-name>MyServlet</servlet-name> <url-pattern>*.jsp</url-pattern> <url-pattern>*.action</url-pattern></servlet-mapping>

Then any url request with the extension jsp or action will match, for example, the following url will be matched
http://localhost:8080/appDemo/user/users.jsp
http://localhost:8080/appDemo/toHome.action

4 Default Match

 <servlet-mapping> <servlet-name>MyServlet</servlet-name> <url-pattern>/</url-pattern></servlet-mapping>

2. Matching order

1. Exact match, servlet-mapping1: <url-pattern>/user/users.html</url-pattern>, servlet-mapping2: <url-pattern>/*</url-pattern>. When a request http://localhost:8080/appDemo/user/users.html comes, servlet-mapping1 matches and no longer matches with servlet-mapping2

2. Path matching, first match the longest path, then match the shortest path servlet-mapping1: <url-pattern>/user/*</url-pattern>, servlet-mapping2: <url-pattern>/*</url-pattern>. When a request http://localhost:8080/appDemo/user/users.html comes, servlet-mapping1 matches and no longer matches with servlet-mapping2

3. Extension matching, servlet-mapping1: <url-pattern>/user/*</url-pattern>, servlet-mapping2: <url-pattern>*.action</url-pattern>. When a request http://localhost:8080/appDemo/user/addUser.action comes, servlet-mapping1 matches and no longer matches with servlet-mapping2

4. The default match is not found in the above servlet, so use the default servlet and configure it as <url-pattern>/</url-pattern>

Issues to be noted

1 Path matching and extension matching cannot be set at the same time

There are only three matching methods, either path matching (starting with the "/" character and ending with the "/*"), extension matching (starting with the "*."), or exact matching. The three matching methods cannot be combined, so don't take it for granted to use wildcards or regular rules.

For example, <url-pattern>/user/*.action</url-pattern> is illegal

Also note: <url-pattern>/aa/*/bb</url-pattern> is an exact match and legal. * here is not the meaning of wild match.

2 "/*" and "/" have different meanings

1. "/*" belongs to path matching and can match all requests. Since the priority of path matching is second only to exact matches, "/*" will override all extension matches. Many 404 errors are caused by this, so this is a particularly bad match pattern, which is generally only used for filter's url-pattern
2. "/" is a special matching pattern in the servlet. The pattern has and only has one instance, with the lowest priority, and will not overwrite any other url-patterns. It will just replace the built-in default servlet of the servlet container. This pattern will also match all requests.
3. After configuring "/", a possible phenomenon is that myServlet will intercept requests in formats such as http://localhost:8080/appDemo/user/addUser.action, http://localhost:8080/appDemo/user/updateUser, but will not intercept http://localhost:8080/appDemo/user/users.jsp, http://localhost:8080/appDemo/index.jsp. This should be because the servlet container has a built-in "*.jsp" matcher, and the priority of extension matching is higher than the default matching, so the above phenomenon occurs.

Tomcat configures the default servlet in the %CATALINA_HOME%/conf/web.xml file, and the configuration code is as follows

 <servlet> <servlet-name>default</servlet-name> <servlet-class>org.apache.catalina.servlets.DefaultServlet</servlet-class> <init-param> <param-name>debug</param-name> <param-value>0</param-value> </init-param> <init-param> <param-name>listings</param-name> <param-value>false</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet><servlet> <servlet-name>jsp</servlet-name> <servlet-class>org.apache.jasper.servlet.JspServlet</servlet-class> <init-param> <param-name>fork</param-name> <param-value>false</param-value> </init-param> <init-param> <param-name>xpoweredBy</param-name> <param-value>false</param-value> </init-param> <load-on-startup>3</load-on-startup> </servlet><servlet-mapping> <servlet-name>default</servlet-name> <url-pattern>/</url-pattern></servlet-mapping> <!-- The mappings for the JSP servlet --><servlet-mapping> <servlet-name>jsp</servlet-name> <url-pattern>*.jsp</url-pattern> <url-pattern>*.jspx</url-pattern></servlet-mapping>

1. You can read http://stackoverflow.com/questions/4140448/difference-between-and-in-servlet-mapping-url-pattern
2. Both "/*" and "/" intercept the loading of static resources, so special attention should be paid to this

IV. Give an example

The result of the actual request mapping

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