要查看tomcat目前用的jdk版本
进入tomcat安装文件夹的bin目录下 执行./version.sh 就可以看到了，查看如下：
Using CATALINA_BASE: /usr/java/apache-tomcat-7.0.41
Using CATALINA_HOME: /usr/java/apache-tomcat-7.0.41
Using CATALINA_TMPDIR: /usr/java/apache-tomcat-7.0.41/temp
Using JRE_HOME: /usr/java/jdk1.7.0_80
Using CLASSPATH: /usr/java/apache-tomcat-7.0.41/bin/bootstrap.jar:/usr/java/apache-tomcat-7.0.41/bin/tomcat-juli.jar
Server version: Apache Tomcat/7.0.41
Server built: Jun 6 2013 11:16:08
Server number: 7.0.41.0
OS Name: Linux
OS Version: 2.6.32-279.el6.x86_64
Architecture: amd64
JVM Version: 1.7.0_80-b15
JVM Vendor: Oracle Corporation
单独查看jdk版本（前提是写进了/usr/bin）
java -version