Detailed explanation of the problem of configuring servlet url-pattern in tomcat

When configuring web.xml for tomcat, servlet is a relatively important issue. Here we discuss several pain points in servlet.

1. Servlet url-pattern matching problem
2. The difference between / and /* in url-pattern
3. Priority issue of url-pattern
4. Root path / matching problem

1 servlet url-pattern matching problem

There are three matching modes for url-pattern : path matching, exact matching, and suffix matching.

1.1 Exact Match

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

Code example: point_down:

<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 you enter the following URLs in the browser, they will be 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

Notice:

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

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

The request http://10.43.11.143/myapp/table?hello will be matched to MyServlet.

1.2 Path Matching

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

Code example: point_down:

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

The path starts with /user/ and the rest of the path can be anything. 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

1.3 Suffix Matching

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

Code example: point_down:

<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 URLs will be matched

http://localhost:8080/appDemo/user/users.jsp

http://localhost:8080/appDemo/toHome.action

Note: Path and suffix matching cannot be set at the same time

Note: Path and extension matching cannot be set at the same time, such as the following three They are all illegal. If set, an error will be reported when starting the tomcat server.

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

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

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

A few examples: point_down:, if you don't understand, please read Chapter 3 of this article

2 The difference between / and /* in url-pattern

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

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

Let’s talk about /* first. /* is relatively easy to understand. It is a type of path matching. In terms of scope, it is the widest path matching, and all requests meet its requirements. In terms of accuracy, it is the path matching with the lowest accuracy ( note! I am talking about path matching ). The priority of path matching is from long to short ( see Chapter 3 of this article for details ), so it is the path matching with the lowest accuracy. Many blogs say that its feature is to match *.jsp . Isn't this nonsense? /* itself is a path matcher, so it can certainly match *.jsp .

Besides / , / is the lowest priority match . When a URL does not match all url-pattern , the URL will go to / for matching. There is no *.jsp restriction at all. The reason why everyone thinks (and objectively it is true) that / will not match *.jsp but /* will match *.jsp is that *.jsp is configured separately in tomcat/conf/web.xml. For details, please see Chapter 3 of this article .

3 URL-pattern priority issues

When a URL matches the matching rules of multiple servlets, the corresponding servlet is matched according to the priority of "exact path > longest path > suffix match".

Example 1: For example, the url-pattern of servletA is /test, and the url-pattern of servletB is /*. At this time, if the url I visit is http://localhost/test, the container will first perform an exact path match and find that /test is exactly matched by servletA. In this case, servletA will be called without caring about servletB.

Example 2: For example, if the url-pattern of servletA is /test/ and the url-pattern of servletB is /test/a/ , when you access http://localhost/test/a, the container will select the servlet with the longest path to match, which is servletB here.

Example 3: For example, the url-pattern of servletA is: *.action, and the url-pattern of servletB is / * . At this time, if the url I visit is http://localhost/test.action, the container will give priority to path matching instead of matching the extension, so as to call servletB.

Then a question arises. Why does /* match *.jsp , but / does not match *.jsp ?

The reason is very simple. There will be the following configuration in tomcat/conf/web.xml

<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>

:point_up_2: It can be clearly seen that *.jsp is the suffix match for the servlet named jsp, and /* is the path match, which has a higher priority than the suffix match, so it can match the file with the suffix jsp. However, / is the lowest level match, which is lower than the suffix match, so the jsp file will not be matched by url-pattern of /.

4 Root path / matching problem

You may have noticed a problem, that is, when the url-pattern is /*, accessing http://localhost:8080/ will result in 404, but accessing http://localhost:8080/index.html will work fine (of course, the premise is that <mvc:default-servlet-handler/> is configured in the spring container). When url-pattern is /, http://localhost:8080/ will automatically forward to http://localhost:8080/index.html without 404. What is the reason?

First of all, we must be clear about what the root directory of a URL, i.e. / (such as http://localhost:8080/), means? Through experiments, we found that / is very special. It will be matched by the url-pattern of /*, but it will not be matched by the url-pattern of /.

In tomcat, / is matched by defaultservlet by default, but its priority is lower than path matching. So when the url-pattern of a servlet is /*, / will be matched by this servlet and not by defaultservlet.

The following snippet found in the tomcat source code can support my view: point_down:

<!-- ===================== Default Welcome File List ===================== -->
<!-- When a request URI refers to a directory, the default servlet looks -->
<!-- for a "welcome file" within that directory and, if present, to the -->
<!-- corresponding resource URI for display. -->
<!-- If no welcome files are present, the default servlet either serves a -->
<!-- directory listing (see default servlet configuration on how to -->
<!-- customize) or returns a 404 status, depending on the value of the -->
<!-- listings setting. -->
<!-- -->
<!-- If you define welcome files in your own application's web.xml -->
<!-- deployment descriptor, that list *replaces* the list configured -->
<!-- here, so be sure to include any of the default values ​​that you wish -->
<!-- to use within your application.

:point_up_2:The above is about Welcome File List , that is, the / path will be forwarded to the web page specified in Welcome File List , that is, the initial page, by default. I will translate part of the above. You can use Google Translate for details. Translation: point_right:

Translation:point_down:

When the request URI points to a directory, the default servlet looks for a "welcome file" in that directory and, if present, at the corresponding resource URI to display. If no welcome file exists, the default servlet either provides a directory listing (see the default servlet configuration for how to customize it) or returns a 404 status, depending on the value of the listing setting.

The reason why / is redirected to the welcome page is the existence of Welcome File List . The prerequisite for Welcome File List to work is that / must be matched by defaultservlet. When the url-pattern of a servlet is /*, / will be matched by this servlet and not by defaultservlet. Therefore, only when the url-pattern of the self-defined servlet is /, http://localhost:8080/ will be automatically forwarded to http://localhost:8080/index.html without 404

Summarize

This is the end of this article about the detailed explanation of the problem of configuring servlet url-pattern in tomcat. For more relevant content about tomcat configuration servlet, please search for previous articles on 123WORDPRESS.COM or continue to browse the related articles below. I hope you will support 123WORDPRESS.COM in the future!