Develop a java servlet interface, mainly to process user requests for weather forecast queries and return corresponding results.

The simple method is to build this xml directly in the servlet's doGet or doPost, and then write back the response.

You need to build a java application server such as tomcat server, and just run this servlet.

There are many tools for Java to build xml, such as JDOM, Dom4J, etc.

If the client requires web service, consider Java Web service frameworks such as Apache CXF, but it is generally not necessary.