查看环境变量CLASSPATH, PATH ,JAVA_HOME-------->mac

                                            终端（命令行）操作

推荐两篇博客：http://elf8848.iteye.com/blog/1582137

                  http://blog.csdn.net/done58/article/details/51138057

查看 JAVA_HOME    命令->set | grep JAVA

添加JAVA_HOME：export JAVA_HOME=$(/usr/libexec/java_home)

查看 PATH 命令->echo $PATH

 添加 PATH export PATH=/Users/snowing/Downloads/apache-maven-3.5.0/bin:$PATH

查看 CLASSPATH：命令->set | more

添加 $export CLASSPATH=${CLASSPATH}:/Users/snowing/Downloads/apache-tomcat-9.0.0.M18/lib/servlet-api.jar

MAC 修改host文件 

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sudo vi /etc/hosts