Why does eclipse edit web. xml?

Eclipse is very slow and drive me crazy. I found a lot of information on the Internet and did not solve it. I have no effect on modifying the configuration file of eclipse. ini, modifying the memory, and disabling many plug-in functions of Eclipse.
I don't think it's my computer. I should change it. It's impossible. I am an I5 processor, 4G memory. Isn't this configuration enough to run eclipse. Therefore, I have rejected all the above reasons and solutions.
After a long morning of hard work, I finally found a foreign post and found the cause and solution.

Another problem is that the computer is disconnected from the network and eclipse is no longer stuck. I believe that web. XML is definitely a problem.

It turns out that the version information in Web. XML is incorrect. You need to modify it based on your servlet version and runtime environment.
Originally, I used Tomcat 6 to support servlet2.5, but because of web. XML is copied from the old project, and the tomcat5 Environment supports servlet2.4. Therefore, version problems cause verification time consumption. You can modify the Web by using specific methods. XML
The version information in, OK.

Modify http://java.sun.com/xml/ns/j2eeHttp://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
For http://java.sun.com/xml/ns/javaeeHttp://java.sun.com/xml/ns/javaee/web-app_2_5.xsd".

Problems with other versions, and so on !!!