Sometimes it is not easy to find a certain version of jdk, here are all the links and the corresponding api
java SE 1.6 various versions jdk api
http://www.oracle.com/technetwork/java/javase/downloads/java-archive-downloads-javase6-419409.html
java SE 1.7 various versions jdk api
http://www.oracle.com/technetwork/java/javase/downloads/java-archive-downloads-javase7-521261.html
java SE 1.8 various versions jdk api
http://www.oracle.com/technetwork/java/javase/downloads/java-archive-javase8-2177648.html