遇到的问题

502：https://www.zhihu.com/question/21647204

银联支付、网银支付、SDK支付等：

https://www.zhihu.com/question/22674209

https://blog.csdn.net/xingkong22star/article/details/50772714

It is indirectly referenced from required .class files：

https://blog.csdn.net/u010735684/article/details/48733671

Unsupported major.minor version 51.0：

https://blog.csdn.net/baidu_18607183/article/details/51942698

https://blog.csdn.net/w410589502/article/details/70886405

https://jingyan.baidu.com/article/380abd0a0ea95f1d90192cf5.html

操作系统中的域名解析过程：

https://blog.csdn.net/DLGDark/article/details/78187094

pom.xml文件一直报错：将工程切换成maven工程；

idea：将所有工程下载到本地的一个文件夹中，idea打开这个文件夹，不要一个个打开单独的工程；

ecplise中，搜索文件时爆出这个错误：Problems encountered during text search. File '' has been skipped, problem while reading；选中工程 -> refresh；

https://jingyan.baidu.com/article/e8cdb32b1579d837052bad39.html

he Tomcat server configuration at ServersTomcat v7.0 Server at localhost-config is missing. Check the server for errors

删掉servers下的tomcat，重新弄一个tomcat;