debian安装的openjdk只包括jre,没有tools.jar,dt.jar，所以要安装openjdk完全版。

sudo apt-get install openjdk-8-jdk

若操作系统中安装多个版本的java，可以采用如下命令来选择具体的java:

sudo update-alternatives --config java

There are 2 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                            Priority   Status

------------------------------------------------------------

* 0            /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java   1061      auto mode

  1            /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java   1061      manual mode

  2            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1051      manual mode

Press enter to keep the current choice[*], or type selection number: 

配置maven,tomcat环境变量