setenv.bat(linux下是setenv.sh)文件是tomcat的自定义变量脚本文件，该脚本文件放置在CATALINA_HOME\bin\或CATALINA_BASE\bin\目录下，该文件需要用户自己创建。在该文件中可以指定java环境变量、jvm参数、catalina参数等。可以设置的参数如下：

变量名	描述
CATALINA_HOME	tomcat的安装目录
CATALINA_BASE	tomcat实例的工作目录
CATALINA_OPTS	start、run或者debug命令执行时的Java虚拟机参数。只能被tomcat自身使用，但在stop和version命令执行时不使用。注意区分JAVA_OPTS
JAVA_HOME	Java开发工具安装路径，仅在使用debug参数启动时有用
JRE_HOME	Java运行时安装路径，如果该参数为空，将使用JAVA_HOME的值，如果JAVA_HOME和JRE_HOME都设置了，将使用JRE_HOME
JAVA_OPTS	用于执行任何命令时的Java虚拟机参数，既能被tomcat自身使用，也在stop和version命令执行时使用。注意区分CATALINA_OPTS
LOGGING_CONFIG	tomcat日志配置变量。例如： set LOGGING_CONFIG="-Djava.util.logging.config.file=%CATALINA_BASE%\conf\logging.properties"
LOGGING_MANAGER	tomcat日志管理变量。例如： set LOGGING_MANAGER="-Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager"

以上只是常用的变量，关于setenv脚本的更多详细内容请参考CATALINA_HOME\bin\目录下的catalina.bat或catalina.sh文件中的介绍。 <!-- more -->

setenv.bat文件示例

@echo off
echo ========  setenv start  ========
rem 设置JRE根目录
set JRE_HOME=D:\Program Files\Java\jdk1.8.0_102\jre
rem 设置JAVA根目录
set JAVA_HOME=D:\Program Files\Java\jdk1.8.0_102
rem 设置JAVA_OPTS
set JAVA_OPTS=%JAVA_OPTS%
rem 设置CATALINA_OPTS
set CATALINA_OPTS=-Dfile.encoding=UTF-8 -Duser.timezone=GMT+8
echo Using JRE_HOME:             %JRE_HOME%
echo Using JAVA_HOME:            %JAVA_HOME%
echo Using JAVA_OPTS:            %JAVA_OPTS%
echo Using CATALINA_OPTS:        %CATALINA_OPTS%
echo ======== setenv over ========

关于CATALINA_HOME 和 CATALINA_BASE

CATALINA_HOME是tomcat的安装目录，CATALINA_BASE是tomcat实例的工作目录。安装目录只有一个，但是实例可以有多个。

CATALINA_BASE包含以下目录和文件：

• bin - 只包含以下文件:

      * setenv.sh (*nix) or setenv.bat (Windows),
      * tomcat-juli.jar
  
     The setenv scripts were described above. The tomcat-juli library
     is documented in the Logging chapter in the User Guide.
  

• conf - 服务配置文件目录 (including server.xml)

• lib - 库文件目录。建议将自己的和第三方的库文件放置在该目录下

• logs - 日志和输出目录

• webapps - 自动加载的web应用目录

• work - web应用的临时工作目录

• temp - JVM临时文件目录(java.io.tmpdir)

CATALINA_HOME包含以下目录和文件：

• bin - 启动和关闭脚本文件目录

     当以下文件不在`CATALINA_BASE/bin`目录时将会被使用:
  
     setenv.sh (*nix), setenv.bat (Windows), tomcat-juli.jar
  

• lib - 库文件目录。建议只放置标准tomcat库文件

关于CATALINA_HOME 和 CATALINA_BASE可以参考RUNNING.txt
其中关于这两个参数的原文描述如下：

==================================================
Advanced Configuration - Multiple Tomcat Instances
==================================================

In many circumstances, it is desirable to have a single copy of a Tomcat
binary distribution shared among multiple users on the same server.  To make
this possible, you can set the CATALINA_BASE environment variable to the
directory that contains the files for your 'personal' Tomcat instance.

When running with a separate CATALINA_HOME and CATALINA_BASE, the files
and directories are split as following:

In CATALINA_BASE:

 * bin  - Only the following files:

           * setenv.sh (*nix) or setenv.bat (Windows),
           * tomcat-juli.jar

          The setenv scripts were described above. The tomcat-juli library
          is documented in the Logging chapter in the User Guide.

 * conf - Server configuration files (including server.xml)

 * lib  - Libraries and classes, as explained below

 * logs - Log and output files

 * webapps - Automatically loaded web applications

 * work - Temporary working directories for web applications

 * temp - Directory used by the JVM for temporary files (java.io.tmpdir)


In CATALINA_HOME:

 * bin  - Startup and shutdown scripts

          The following files will be used only if they are absent in
          CATALINA_BASE/bin:

          setenv.sh (*nix), setenv.bat (Windows), tomcat-juli.jar

 * lib  - Libraries and classes, as explained below

In the default configuration the JAR libraries and classes both in
CATALINA_BASE/lib and in CATALINA_HOME/lib will be added to the common
classpath, but the ones in CATALINA_BASE will be added first and thus will
be searched first.

The idea is that you may leave the standard Tomcat libraries in
CATALINA_HOME/lib and add other ones such as database drivers into
CATALINA_BASE/lib.