JDK 7 API 官方下载地址：
http://www.oracle.com/technetwork/java/javase/documentation/java-se-7-doc-download-435117.html
JDK 8 API 官方下载地址：
http://www.oracle.com/technetwork/java/javase/documentation/jdk8-doc-downloads-2133158.html
JDK及相关文档的下载都在这个页面：
http://www.oracle.com/technetwork/java/javase/downloads/index.html
Java Language and Virtual Machine Specifications
http://docs.oracle.com/javase/specs/