Bug 21583 Generate Javadoc won't link prereqed projects
In the export wizard for generating javadoc, there is no easy way to link the javadoc from a prereqed project. The wizard has a screen for linking in javadoc from libraries included in the classpath, but projects in the classpath do not show up. I got a temporary workaround from the news group. Just add a "-link URL_TO_OTHER_PROJECT_JAVADOC" in the javadoc options page, but there should be an easier way to do this.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javadocexport/JavadocStandardWizardPage.java
for (int i= 0; i < entries.length; i++) {
			IClasspathEntry curr= entries[i];
			switch (curr.getEntryKind()) {
				case IClasspathEntry.CPE_LIBRARY:
					IPackageFragmentRoot el = jproject.getPackageFragmentRoot(curr.getPath().toOSString());
					if(el != null) {
						if (!referencedClasses.contains(el)) {
								referencedClasses.add(el);
						}
					}
					break;
				case IClasspathEntry.CPE_PROJECT:
					IProject reqProject= (IProject)fStore.getRoot().findMember(curr.getPath().lastSegment());
					IJavaProject javaProject = JavaCore.create(reqProject);
					if (javaProject != null && javaProject.getProject().isOpen()) {
						getElements(referencedClasses, javaProject, visited);
					}
					break;
				case IClasspathEntry.CPE_SOURCE:
					if (!sourceFolderFound) {
						
						IPath outputLocation= jproject.getOutputLocation();
						IResource resource= fStore.getRoot().findMember(outputLocation);
						if (resource != null) {
							IJavaElement javaElement= JavaCore.create(resource);
							if((javaElement!= null) && (!javaElement.equals(fWizard.getProject()))) {
								URL url= JavaDocLocations.getJavadocBaseLocation(javaElement);
								if(url != null)
									referencedClasses.add(javaElement);
							}