Just create a Java project using JDT API and then enable Seam support for the project:
IProject project = ...; // Your Java project.
org.jboss.tools.common.model.util.EclipseResourceUtil.addNatureToProject(project, org.jboss.tools.seam.core.ISeamProject.NATURE_ID); // Enables Seam builder and nature.
if(!project.hasNature(org.jboss.tools.jst.web.kb.IKbProject.NATURE_ID)) {
org.jboss.tools.common.model.util.EclipseResourceUtil.addNatureToProject(project, org.jboss.tools.jst.web.kb.IKbProject.NATURE_ID); // Enables JBoss Tools KnowledgeBase builder/nature required by Seam/JSF code completion/validation/hyperlinks.
}
org.jboss.tools.common.model.util.EclipseResourceUtil.addBuilderToProject(project, org.eclipse.wst.validation.internal.plugin.ValidationPlugin.VALIDATION_BUILDER_ID); // Enables WST validation which is required by Seam validation.
Or you can create a WTP dynamic web project instead of plain Java project if you want a full JSF support on XHTML/JSPs.