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How to analyze the basic configuration process of JavaWeb project web.xml, in view of this problem, this article introduces the corresponding analysis and solution in detail, hoping to help more partners who want to solve this problem to find a more simple and feasible method.

one。 Theoretical preparation

First of all, I remember the xml rule, there must be one and only one root node, case-sensitive, tags are not nested, and must be paired.

Is web.xml necessary? No, as long as you don't need the configuration information in it, but it is convenient to use this file in a large web project, and it will be very complicated if not.

So what are all the things web.xml can do? In fact, as many tag elements are defined in web.xml 's Schema file, the tag elements defined in its schema file can appear in web.xml and it can have those defined functions. The schema file for web.xml is defined by Sun, and the root element of each web.xml file must indicate which schema file the web.xml uses. Let's look at an example:

Db index.html index.htm index.jsp default.html default.htm default.jsp

two。 Tag element

Specify the welcome page

Index.jsp index1.jsp

The above example specifies two welcome pages, starting with the first one in order, and if the first one exists, the first one is displayed, and the latter does not work. If the first one doesn't exist, find the second, and so on.

About the welcome page: when you visit a website, the first page you see by default is called the welcome page. Generally speaking, the home page acts as the welcome page. Normally, we specify the welcome page in web.xml. But web.xml is not a necessary document for Web. Without web.xml, the website can still work properly. It's just that after the functions of the website become more complex, web.xml is indeed very useful, so the dynamic web projects created by default have a web.xml file under the WEB-INF folder.

For tomcat, when you specify only a root name of web, no specific page, and when you visit a web, if the welcome page is configured in the web.xml file, then the specified page is returned as the welcome page. If there is no web.xml file in the text, or although there is web.xml, but web.xml does not specify the welcome page, it looks for the index.html file by default. Return index.html to the browser as a welcome page. If you don't find index.html,tomcat, go to index.jsp. Find index.jsp and return it as a welcome page. If neither index.html nor index.jsp is found, and the welcome page is not specified in the web.xml file, then tomcat does not know which file to return, and it displays the page of The requested resource (/ XXX) is not available (I have had this problem). Where XXX represents the root name of web. But if you specify a specific page, it can be accessed normally.

Naming and customizing URL

Servlet1 net.test.TestServlet servlet1 * .do

Url-pattern means that all .do files are processed by TestServlet.

Custom initialization parameters

Servlet1 net.test.TestServlet userName Tommy E-mail Tommy@163.com

With the above configuration, you can call getServletConfig (). GetInitParameter ("param1") in servlet to get the corresponding value of the parameter name.

/ / context parameters: declare initialization parameters within the scope of application. ContextParameter test It is a test parameter. / / in servlet, you can use getServletContext () .getInitParameter ("context/param")

Get

Specify the error handling page, which can be specified through the exception Type or error Code.

404 / error404.jsp-- java.lang.Exception / exception.jsp java.lang.NullException / error.jsp

Set filters: for example, set a coding filter to filter all resources

XXXCharaSetFilter net.test.CharSetFilter XXXCharaSetFilter / *

6. Set up listeners

What's the use of what's in web.xml? There's no other use! Is to configure the listener class, which can capture the start and stop of the server! Do the corresponding operation in the methods inside the start and stop triggers! It must be configured in web.xml to be used! There is not only one listener element in web.xml, but it is executed sequentially when there are multiple elements.

How to pass parameters to listener in web.xml?

The full path to the listener class

Initialization parameters cannot be written in the listener; the effect of initialization parameters can be achieved in another way: 1. Write a properties file, write the initialization parameter values in the file, 2. You can get the values in the properties file (written in static blocks) in the listener.

Sets the session (Session) expiration time in minutes

sixty

In addition to these tag elements, what other tag elements can be added to web.xml, and what can those tag elements do? We only need to look at web.xml 's schema file to find out. If you look at the pattern file directly, you can't understand it. You can find some Chinese tutorials to take a look at.

three。 Remaining problems

I always encounter some priority problems about loading in the project, and I have also encountered similar problems recently, so I looked up the materials and summarized them. Some of the following are reproduced by others. After all, they write well, so I don't repeat the wheels. I just added a little bit of my own embellishments. First of all, it is certain that the loading order is independent of their order in the web.xml file. That is, filter will not be loaded first because filter is written in front of listener. The final conclusion is: listener-> filter-> servlet. If a session is not accessed for a certain period of time, the server can discard it to save memory. You can explicitly set the timeout value for a single session object by using HttpSession's setMaxInactiveInterval method, or you can use the session-config element to set the default timeout value.

Instructs the server which file to use when it receives a URL that references a directory name instead of a file name.

How to configure url-pattern in web.xml? First of all, you need to know the role of url-pattern in web.xml. It is an external interface to access the DoGetDemo class. You can define it yourself, and then write this configuration content in IE. You can look at an example picture I wrote for you, and you should understand it at once. Take SimpleHello.java as an example. When you visit, you can enter the following URL http://192.168.0.67:8888/book/hello so that the server can find the ch06.SimpleHello class through / hello, so you can define the content inside. Then access the servlet in the application directory.

Why do you need servlet-class when you have url-pattern in web.xml? Url-pattern indicates what format url enters the servlet, and servlet-class indicates which java class processes the request. When a request comes, first go to servlet-mapping to find the corresponding url-pattern according to the requested url, find the url-pattern, find the servlet-name, and then find the corresponding servlet-class according to the corresponding servlet-name in servlet-name and servlet. The specific business logic is written in the java class corresponding to the servlet-class!

The answer to the question on how to analyze the basic configuration process of JavaWeb project web.xml is shared here. I hope the above content can be of some help to you. If you still have a lot of doubts to be solved, you can follow the industry information channel for more related knowledge.

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