Plugin installation fails because required items are missing

Question

I tried to install Web Tool Platform for Eclipse but I can not succeed due to the following error.

Cannot complete the install because one or more required items could not be found.
Software being installed: CXF Web Services 1.1.0.v201201312103-7H79FHxFAKlbotH5e9l3vAA6MBG (org.eclipse.jst.ws.cxf.feature.feature.group 1.1.0.v201201312103-7H79FHxFAKlbotH5e9l3vAA6MBG) Missing requirement: Java EE Component 1.1.501.v201108102200 (org.eclipse.jst.j2ee 1.1.501.v201108102200) requires 'bundle org.eclipse.emf.codegen [2.2.0,3.0.0)' but it could not be found
Missing requirement: Java EE Component 1.1.501.v201109131730 (org.eclipse.jst.j2ee 1.1.501.v201109131730) requires 'bundle org.eclipse.emf.codegen [2.2.0,3.0.0)' but it could not be found
Missing requirement: Java EE Component 1.1.600.v201203142300 (org.eclipse.jst.j2ee 1.1.600.v201203142300) requires 'bundle org.eclipse.emf.codegen [2.2.0,3.0.0)' but it could not be found
Missing requirement: Java EE Component 1.1.600.v201205030130 (org.eclipse.jst.j2ee 1.1.600.v201205030130) requires 'bundle org.eclipse.emf.codegen [2.2.0,3.0.0)' but it could not be found
Missing requirement: Java EE Component 1.1.600.v201205170400 (org.eclipse.jst.j2ee 1.1.600.v201205170400) requires 'bundle org.eclipse.emf.codegen [2.2.0,3.0.0)' but it could not be found
Missing requirement: Java EE Component 1.1.601.v201207101600 (org.eclipse.jst.j2ee 1.1.601.v201207101600) requires 'bundle org.eclipse.emf.codegen [2.2.0,3.0.0)' but it could not be found
Cannot satisfy dependency: From: CXF Web Services Core 1.1.0.v201205012246 (org.eclipse.jst.ws.cxf.core 1.1.0.v201205012246) To: bundle org.eclipse.jst.j2ee [1.1.0,1.2.0) Cannot satisfy dependency: From: CXF Web Services 1.1.0.v201201312103-7H79FHxFAKlbotH5e9l3vAA6MBG (org.eclipse.jst.ws.cxf.feature.feature.group 1.1.0.v201201312103-7H79FHxFAKlbotH5e9l3vAA6MBG) To: org.eclipse.jst.ws.cxf.core [1.1.0.v201205012246]

Actually this happens a lot of times when I try to install additional software via Help > Install New Software. E.g. I had it some times when trying to install the Android SDK.
Though I could usually solve it while fiddling around with it I can't believe installing plug ins is such a pain.

So I think I might missing some very basic things but I can not find a hint. So it would be a great if you could help me to fix this particular problem but also provide some information how to tackle such problems in a more general matter.

Answer 1

On the bottom of the "Install" dialog, make sure that "Contact all update sites during install to find required software" is checked.

This assumes that the necessary, default software sites are still properly configured (haven't been disabled, removed, etc.) and available. These are configured under Windows, Preferences, Install/Update, Available Software Sites. (Unfortunately, I don't see a "restore to defaults" button here.) For at least the latest version of Eclipse (4.2/Juno), you'll want to ensure you have at least the following sites configured and enabled here:

• Juno : http://download.eclipse.org/releases/juno
• The Eclipse Project Updates : http://download.eclipse.org/eclipse/updates/4.2
• The Eclipse Web Tools Platform (WTP) software repository : http://download.eclipse.org/webtools/repository/juno