Recommended frameworks, libraries and concepts

What are the various concepts/data types/tools in java those must be known by a good programmer? For example; enum,collection,multimap, etc

Please also suggest various libraries/open source framework/libraries which can be helpf开发者_JS百科ul to handle any specific task or can make a task handy. For example

Spring Dao, Java Persistence API for handling database operations effectively.

the Collections framework in java has most collections you will ever need. you can find the classes and interfaces in the java.util package

the java.io package has (most) everything you need for most file and stream handling

For dealing with Collection related code I would highly recommend Google Guaua Library.

And for almost everything else Spring Framework is there :)