Eclipse takes long time to save web.xml

Eclipse can run slow due to various reasons.

Large number of projects

If you have a large number of projects, Eclipse needs to process all of them when doing a clean build on all projects, when searching for references (types / resources), when validation needs to occur. You can use working sets to organize your projects, and hide the ones you're not using.

Validations on projects

Eclipse has the concept of validators that can be put on projects. This can lead to a lot of processing (ex: validation of xml, xsd, jsps / ....). Sometimes it can be usefull to disable certain validators that you don't really need.

Memory

Memory can be tweaked by supplying standard java memory parameters in the eclipse.ini file. If insufficient memory is allocated to Eclipse, it can lead up to a lot of garbage collection, causing it to slow down.

Plugins

Some third party plugins introduce builders / validators that get applied on projects, that cuold slow down eclipse.

Make sure you use the lastest version of Eclipse, don't put too much projects in your workspace, and keep the third party plugins to a minimum.