step1：查看java的执行路径
[root@bogon hadoop]# which java
/usr/bin/java
[root@bogon hadoop]# which javac
/usr/local/java/jdk1.8.0_11/bin/javac
step2：把java执行路径ln -s 到新的jdk下的 java 和 javac 上
[root@bogon hadoop]# rm -rf /usr/bin/java
[root@bogon hadoop]# ln -s $JAVA_HOME/bin/java /usr/bin/java
[root@bogon hadoop]# which java
/usr/bin/java
[root@bogon hadoop]# rm -rf /usr/bin/javac
[root@bogon hadoop]# ln -s $JAVA_HOME/bin/javac /usr/bin/javac
[root@bogon hadoop]# which javac
/usr/bin/javac
用java -version查看，已切换到新的jdk版本
参考链接：
https://www.jianshu.com/p/a1c540f30d40
https://www.cnblogs.com/YatHo/p/7526852.html
