To convert a Java Project to a Web Project switch to or open the Resource Perspective of the project, in the root of the project. Open the .project file and make sure the builders and natures are present that are needed for a web project. See the example below, the name should be the name of your project, the most important nodes are the nature children in the natures node:

<projectdescription><name>testProject</name><comment></comment><projects></projects><buildspec><buildcommand><name>org.eclipse.jdt.core.javabuilder</name><arguments></arguments></buildcommand><buildcommand><name>org.eclipse.wst.common.project.facet.core.builder</name><arguments></arguments></buildcommand><buildcommand><name>org.eclipse.wst.validation.validationbuilder</name><arguments></arguments></buildcommand></buildspec><natures><nature>org.eclipse.wst.common.project.facet.core.nature</nature><nature>org.eclipse.jdt.core.javanature</nature><nature>org.eclipse.wst.common.modulecore.ModuleCoreNature</nature><nature>org.eclipse.jem.workbench.JavaEMFNature</nature></natures></projectdescription>

Once you’ve updated the .project file you can close the file and right click and choose properties on the project. When the properties window opens click on Project Facets. The Facets grid is probably empty, click the Modify Project button. Check the Dynamic Web Module and Java Facets, choose the Java and Servlet version that applies to your project. Click Next and specify the existing or new location of your src and web content directories. Click Finish.

As a final step I would recommend modifying the build path to compile your source directly into your /WEB-INF/classes directory by selecting Java Build Path and modifying the Default output directory.

Now you should be able to create a local tomcat server, or if you’ve already created one you should be able to add the project to the server by right clicking the server and choosing Add and Remove Projects.

Original article at http://greatwebguy.com/programming/eclipse/converting-a-java-project-to-a-dynamic-web-project-in-eclipse/.