增加Java开发效率的库

Guava
https://code.google.com/p/guava-libraries/

Joda-Time
http://www.joda.org/joda-time/
http://www.ibm.com/developerworks/cn/java/j-jodatime.html

Apache commons-lang (和Guava部分重叠)
http://commons.apache.org/proper/commons-lang/