JAVA入门各种API参考

java sdk：

https://docs.oracle.com/javase/8/docs/api/

servlet api：

http://tomcat.apache.org/tomcat-8.5-doc/servletapi/index.html

jdbc: 

https://docs.oracle.com/javase/8/docs/technotes/guides/jdbc/

c3p0：

https://www.mchange.com/projects/c3p0/

freemarker:

http://freemarker.foofun.cn/

https://freemarker.apache.org/

httpclient:

http://hc.apache.org/httpcomponents-client-ga/httpclient/apidocs/