Eclipse Minify Plugin
You can install the plugin through its update site https://raw.githubusercontent.com/mnlipp/EclipseMinifyBuilder/gh-pages/update-site/.
Enable the builder for your project in Project/Configure. Then, for each file that you want to be minified, configure a minifier in the file's properties dialog.
Version 0.9.2 supports both YUICompressor and Google Closure Compiler.
Version 0.9.5 supports generation of source maps with the Google Closure Compiler.