A detailed description of the servlet's Url-pattern matching rules

I. Overview

When matching a URL request with a servlet or filter, the key is to match the rules, but the matching rules in the servlet container are neither simple nor regular expressions, but rather easily confused by their own rules. This article provides a detailed example of this. The following instructions are validated on the Tomcat server.

First introduce the concept of matching, the example code. In an app, such as the Web. xml file named MyApp, the following information is available:

<servlet>    <Servlet-name>Myservlet</Servlet-name>    <Servlet-class>Com.nau.MyServlet</Servlet-class></servlet><servlet-mapping>    <Servlet-name>Myservlet</Servlet-name>    <Url-pattern>Xxxxxx</Url-pattern>    <Url-pattern>Yyyyyyy</Url-pattern></servlet-mapping>

The configuration information above, where the <servlet> tag is first configured to declare a servlet, including the name of the servlet and the corresponding Java class name.
Where the <servlet-mapping> tag declares a matching rule corresponding to the servlet, each <url-pattern> tag represents 1 matching rules.

When the browser initiates a URL request and the request is sent to the servlet container, the container first subtracts the requested URL from the path of the current application context as a mapped URL for the servlet, such as the URL is http://10.43.11.143/myapp/kata/ Detail.html, the application context is MyApp, the container will Http://10.43.11.143/myapp removed, the remainder of the/kata/detail.html to do the servlet mapping matching. This mapping matching process is prioritized (described later in the order of precedence rules), and when a servlet match succeeds, the remaining servlet is not ignored.

Note that the filter matches the same rules as the servlet, but for filter, it does not match just one servlet as the servlet, because the filter collection is a chain, so there will be only a different order of processing, instead of just selecting one filter. The filter is processed in the same order as the filter-mapping defined in Web. Xml.

Here we describe in detail the various matching rules

Second, exact match

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

The configuration information is as follows:

<servlet-mapping>    <Servlet-name>Myservlet</Servlet-name>    <Url-pattern>/kata/detail.html</Url-pattern>    <Url-pattern>/demo.html</Url-pattern>    <Url-pattern>/table</Url-pattern></servlet-mapping>

When several URLs are entered in the browser, they are matched to the servlet
Http://10.43.11.143/myapp/kata/detail.html
Http://10.43.11.143/myapp/demo.html
Http://10.43.11.143/myapp/table

Attention:

http://10.43.11.143/myapp/table/is an illegal URL and will not be recognized as a http://10.43.11.143/myapp/table

In addition, the above URL can be followed by arbitrary query conditions, will be matched, such as

Http://10.43.11.143/myapp/table?hello this request will be matched to Myservlet.

Third, extension matching

If the matching rules are

< servlet-mapping >    < Servlet-name > Myservlet</servlet-name>    <Url-pattern  >*.jsp</url-pattern></servlet-mapping >

Any URL requests with the extension JSP (file name and path arbitrary) will match, such as the following URLs will be matched
http://10.43.11.143/myapp/demo.jsp
http://10.43.11.143/myapp/test.jsp

Four, path matching

If the matching rules are

 <  servlet-mapping  >  <  servlet-name  >  myservlet</ servlet-name  >  <  url-pattern  > /kata/*</ url-pattern    </ servlet-mapping  >  

The requested ULR as long as the path before (MyApp) is/kata, and the subsequent path can be arbitrary. For example, the following URLs will be matched.
Http://10.43.11.143/myapp/kata/demo.html
http://10.43.11.143/myapp/kata/test.jsp
Http://10.43.11.143/myapp/kata/test/detail.html

Http://10.43.11.143/myapp/kata/action

http://10.43.11.143/myapp/kata/action/

Note: The path and extension matching cannot be set at the same time, such as the following three <url-pattern> is illegal, if set, start Tomcat server will error.

<url-pattern>/kata/*.jsp</url-pattern>

<url-pattern>/*.jsp</url-pattern>

<url-pattern>he*.jsp</url-pattern>

Also note:<url-pattern>/aa/*/bb</url-pattern>
This is the exact match, the URL must be/aa/*/bb, and here the * is not the meaning of the wildcard

V. Match any URL

If <url-pattern> is configured as one of the following two types of

<url-pattern>/</url-pattern>

<url-pattern>/*</url-pattern>

All URLs can be matched. where/* is the path match, just the path is/.

Vi. Order of Precedence

When a URL matches a match rule for more than one servlet, the corresponding servlet is matched to a priority such as "exact path > Longest path > Extension". Examples are as follows:

Example 1: For example Servleta Url-pattern for/TEST,SERVLETB url-pattern for * *, this time, if I visit the URL is http://localhost/test, This time the container will be the exact path matching, found that the/test is precisely matched by Servleta, then go to call Servleta, do not go to the tube servletb.

Example 2: For example Servleta Url-pattern for/test/*, and Servletb Url-pattern for/test/a/*, at this time to visit http://localhost/test/a, The container chooses the longest path of the servlet to match, which is where the SERVLETB.

Example 3: For example Servleta url-pattern:*.action, Servletb url-pattern is/*, this time, if I visit the URL is http://localhost/ Test.action, this time the container will prioritize path matching instead of matching the extension so that it calls SERVLETB.

Attention:

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

There are only three matching methods, either path matching ( beginning with the "/" character and ending with "/*" ) or extension matching ( "*."). Start ), either exact match, three matching methods cannot be combined, do not assume that wildcards or regular rules are used.

such as <url-pattern>/user/*.action</url-pattern> is illegal

Also note that:<url-pattern>/aa/*/bb</url-pattern> is precisely matched, legal, and here the * is not the meaning of the wildcard

2 "/*" and "/" do not have the same meaning

• "/*" is a path match and can match all request, because the path match priority is second only to the exact match, so "/*" overrides all extension matches, many 404 errors are caused, so this is a particularly bad match pattern, Generally only for filter url-pattern
• "/" is a special matching pattern in the servlet that has only one instance of the pattern, has the lowest priority, does not overwrite any other url-pattern, but replaces the built-in default servlet of the Servlet container, which also matches all request.
• After configuring "/", one possible phenomenon is that myservlet will intercept such as Http://localhost:8080/appDemo/user/addUser.action, http://localhost:8080/appDemo/ User/updateuser in the format of the request, but does not intercept http://localhost:8080/appDemo/user/users.jsp, http://localhost:8080/appDemo/ Index.jsp, this is because the servlet container should have a built-in "*.jsp" match, and the extension match has a higher precedence than the default match.

Tomcat configures the default servlet in the%catalina_home%\conf\web.xml file, with the following configuration code

　　

<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>

• Can read Http://stackoverflow.com/questions/4140448/difference-between-and-in-servlet-mapping-url-pattern
• "/*" and "/" will block the loading of static resources, requiring special attention

Iv. Examples of

The mapped URL	The corresponding servlet
/hello	Servlet1
/bbs/admin/*	Servlet2
/bbs/*	Servlet3
*.jsp	Servlet4
/	Servlet5

Results of Actual request mappings

Remove the remaining path of the context path	Servlet that handles the request
/hello	Servlet1
/bbs/admin/login	Servlet2
/bbs/admin/index.jsp	Servlet2
/bbs/display	Servlet3
/bbs/index.jsp	Servlet3
/bbs	Servlet3
/index.jsp	Servler4
/hello/index.jsp	Servlet4
/hello/index.html	Servlet5
/news	Servlet5

This article describes the matching rules for servlets in detail. In general, there are three ways to match the exact, path and extension, and the priority is introduced.

This article transferred from: https://www.cnblogs.com/51kata/p/5152400.html

A detailed description of the servlet's Url-pattern matching rules