tomcat启动报错：Neither the JAVA_HOME nor the JRE_HOME environment variable is defined

windows系统：

部署了一个tomcat8.5.15，bin目录下startup.bat执行，结果提示neither the java_home nor the jre_home environment variable is defined at least one of these environment variable is needed to run this program。

解决方式：

在setclasspath.bat的开头声明环境变量。如图所示：

先看tomcat的startup.bat，它调用了catalina.bat,而catalina.bat则调用了setclasspath.bat。只要在setclasspath.bat的开头声明环境变量，如我的就是：

rem ---------------------------------------------------------------------------
rem set classpath and java options
rem
rem $id: setclasspath.bat 505241 2007-02-09 10:22:58z jfclere $
rem ---------------------------------------------------------------------------

set java_home=e:\java\jdk1.8.0_151
set jre_home=e:\java\jre8

rem make sure prerequisite environment variables are set
if not "%java_home%" == "" goto gotjdkhome
if not "%jre_home%" == "" goto gotjrehome
echo neither the java_home nor the jre_home environment variable is defined
echo at least one of these environment variable is needed to run this program
goto exit
......

这样在每次运行startup.bat时就注册了java_home，jre_home。控制台窗口关闭后，这两个变量也将消失，不会再占用内存

linux系统：

在tomcat的bin目录下，编辑catalina.sh文件，加入

export java_home=/usr/local/java/jdk1.8.0_151

export jre_home=/usr/local/java/jdk1.8.0_151/jre

这两行，重新启动就正常！