在之前的环境搭建那篇文章里是通过直接运行BootStarp的main函数来启动的，只是加了一个catalina.home的系统属性。而正常情况下启动Tomcat是通过运行脚本的方式，这个就涉及到建立工程时拷贝过来的script目录下的一堆脚本文件了。
以我的windows系统举例，实际上最终是执行startup.bat这个批处理文件来启动tomcat的。
那么启动分析就冲这个文件开始吧：
一、分析startup.bat文件
@echo off rem Licensed to the Apache Software Foundation (ASF) under one or more rem contributor license agreements. See the NOTICE file distributed with rem this work for additional information regarding copyright ownership. rem The ASF licenses this file to You under the Apache License, Version 2.0 rem (the "License"); you may not use this file except in compliance with rem the License. You may obtain a copy of the License at rem rem http://www.apache.org/licenses/LICENSE-2.0 rem rem Unless required by applicable law or agreed to in writing, software rem distributed under the License is distributed on an "AS IS" BASIS, rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. rem See the License for the specific language governing permissions and rem limitations under the License. if "%OS%" == "Windows_NT" setlocal rem --------------------------------------------------------------------------- rem Start script for the CATALINA Server rem rem $Id: startup.bat 895392 2010-01-03 14:02:31Z kkolinko $ rem --------------------------------------------------------------------------- rem Guess CATALINA_HOME if not defined set "CURRENT_DIR=%cd%" if not "%CATALINA_HOME%" == "" goto gotHome set "CATALINA_HOME=%CURRENT_DIR%" if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome cd .. set "CATALINA_HOME=%cd%" cd "%CURRENT_DIR%" :gotHome if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome echo The CATALINA_HOME environment variable is not defined correctly echo This environment variable is needed to run this program goto end :okHome set "EXECUTABLE=%CATALINA_HOME%\bin\catalina.bat" rem Check that target executable exists if exist "%EXECUTABLE%" goto okExec echo Cannot find "%EXECUTABLE%" echo This file is needed to run this program goto end :okExec rem Get remaining unshifted command line arguments and save them in the set CMD_LINE_ARGS= :setArgs if ""%1""=="""" goto doneSetArgs set CMD_LINE_ARGS=%CMD_LINE_ARGS% %1 shift goto setArgs :doneSetArgs call "%EXECUTABLE%" start %CMD_LINE_ARGS% :end
第1行@echo off的是关闭显示命令行自身的意思，接下来一大堆rem是注释，第17行if "%OS%" == "Windows_NT" setlocal是要临时修改系统变量，方便批处理运行。第26到33行的作用是设置CATALINA_HOME环境变量，如果操作系统中没设置，则将当前运行脚本的目录作为该环境变量的值，最终都会跳转到37行。39到46行验证CATALINA_HOME变量所示目录下的catalina.bat文件是否存在，不存在则批处理直接结束。48到55行将运行脚本前如果设置了其他参数，将参数保存到CMD_LINE_ARGS变量中。最后第57行执行catalina.bat批处理文件，注意，该行后面跟着两个参数，第1个参数是start。
二、分析catalina.bat文件
@echo off rem Licensed to the Apache Software Foundation (ASF) under one or more rem contributor license agreements. See the NOTICE file distributed with rem this work for additional information regarding copyright ownership. rem The ASF licenses this file to You under the Apache License, Version 2.0 rem (the "License"); you may not use this file except in compliance with rem the License. You may obtain a copy of the License at rem rem http://www.apache.org/licenses/LICENSE-2.0 rem rem Unless required by applicable law or agreed to in writing, software rem distributed under the License is distributed on an "AS IS" BASIS, rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. rem See the License for the specific language governing permissions and rem limitations under the License. if "%OS%" == "Windows_NT" setlocal rem --------------------------------------------------------------------------- rem Start/Stop Script for the CATALINA Server rem rem Environment Variable Prerequisites rem rem Do not set the variables in this script. Instead put them into a script rem setenv.bat in CATALINA_BASE/bin to keep your customizations separate. rem rem CATALINA_HOME May point at your Catalina "build" directory. rem rem CATALINA_BASE (Optional) Base directory for resolving dynamic portions rem of a Catalina installation. If not present, resolves to rem the same directory that CATALINA_HOME points to. rem rem CATALINA_OPTS (Optional) Java runtime options used when the "start", rem "run" or "debug" command is executed. rem Include here and not in JAVA_OPTS all options, that should rem only be used by Tomcat itself, not by the stop process, rem the version command etc. rem Examples are heap size, GC logging, JMX ports etc. rem rem CATALINA_TMPDIR (Optional) Directory path location of temporary directory rem the JVM should use (java.io.tmpdir). Defaults to rem %CATALINA_BASE%\temp. rem rem JAVA_HOME Must point at your Java Development Kit installation. rem Required to run the with the "debug" argument. rem rem JRE_HOME Must point at your Java Runtime installation. rem Defaults to JAVA_HOME if empty. If JRE_HOME and JAVA_HOME rem are both set, JRE_HOME is used. rem rem JAVA_OPTS (Optional) Java runtime options used when any command rem is executed. rem Include here and not in CATALINA_OPTS all options, that rem should be used by Tomcat and also by the stop process, rem the version command etc. rem Most options should go into CATALINA_OPTS. rem rem JAVA_ENDORSED_DIRS (Optional) Lists of of semi-colon separated directories rem containing some jars in order to allow replacement of APIs rem created outside of the JCP (i.e. DOM and SAX from W3C). rem It can also be used to update the XML parser implementation. rem Defaults to $CATALINA_HOME/endorsed. rem rem JPDA_TRANSPORT (Optional) JPDA transport used when the "jpda start" rem command is executed. The default is "dt_socket". rem rem JPDA_ADDRESS (Optional) Java runtime options used when the "jpda start" rem command is executed. The default is 8000. rem rem JPDA_SUSPEND (Optional) Java runtime options used when the "jpda start" rem command is executed. Specifies whether JVM should suspend rem execution immediately after startup. Default is "n". rem rem JPDA_OPTS (Optional) Java runtime options used when the "jpda start" rem command is executed. If used, JPDA_TRANSPORT, JPDA_ADDRESS, rem and JPDA_SUSPEND are ignored. Thus, all required jpda rem options MUST be specified. The default is: rem rem -agentlib:jdwp=transport=%JPDA_TRANSPORT%, rem address=%JPDA_ADDRESS%,server=y,suspend=%JPDA_SUSPEND% rem rem LOGGING_CONFIG (Optional) Override Tomcat's logging config file rem Example (all one line) rem set LOGGING_CONFIG="-Djava.util.logging.config.file=%CATALINA_BASE%\conf\logging.properties" rem rem LOGGING_MANAGER (Optional) Override Tomcat's logging manager rem Example (all one line) rem set LOGGING_MANAGER="-Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager" rem rem TITLE (Optional) Specify the title of Tomcat window. The default rem TITLE is Tomcat if it's not specified. rem Example (all one line) rem set TITLE=Tomcat.Cluster#1.Server#1 [%DATE% %TIME%] rem rem rem rem $Id: catalina.bat 1344732 2012-05-31 14:08:02Z kkolinko $ rem --------------------------------------------------------------------------- rem Suppress Terminate batch job on CTRL+C if not ""%1"" == ""run"" goto mainEntry if "%TEMP%" == "" goto mainEntry if exist "%TEMP%\%~nx0.run" goto mainEntry echo Y>"%TEMP%\%~nx0.run" if not exist "%TEMP%\%~nx0.run" goto mainEntry echo Y>"%TEMP%\%~nx0.Y" call "%~f0" %* <"%TEMP%\%~nx0.Y" rem Use provided errorlevel set RETVAL=%ERRORLEVEL% del /Q "%TEMP%\%~nx0.Y" >NUL 2>&1 exit /B %RETVAL% :mainEntry del /Q "%TEMP%\%~nx0.run" >NUL 2>&1 rem Guess CATALINA_HOME if not defined set "CURRENT_DIR=%cd%" if not "%CATALINA_HOME%" == "" goto gotHome set "CATALINA_HOME=%CURRENT_DIR%" if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome cd .. set "CATALINA_HOME=%cd%" cd "%CURRENT_DIR%" :gotHome if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome echo The CATALINA_HOME environment variable is not defined correctly echo This environment variable is needed to run this program goto end :okHome rem Copy CATALINA_BASE from CATALINA_HOME if not defined if not "%CATALINA_BASE%" == "" goto gotBase set "CATALINA_BASE=%CATALINA_HOME%" :gotBase rem Ensure that any user defined CLASSPATH variables are not used on startup, rem but allow them to be specified in setenv.bat, in rare case when it is needed. set CLASSPATH= rem Get standard environment variables if not exist "%CATALINA_BASE%\bin\setenv.bat" goto checkSetenvHome call "%CATALINA_BASE%\bin\setenv.bat" goto setenvDone :checkSetenvHome if exist "%CATALINA_HOME%\bin\setenv.bat" call "%CATALINA_HOME%\bin\setenv.bat" :setenvDone rem Get standard Java environment variables if exist "%CATALINA_HOME%\bin\setclasspath.bat" goto okSetclasspath echo Cannot find "%CATALINA_HOME%\bin\setclasspath.bat" echo This file is needed to run this program goto end :okSetclasspath call "%CATALINA_HOME%\bin\setclasspath.bat" %1 if errorlevel 1 goto end rem Add on extra jar file to CLASSPATH rem Note that there are no quotes as we do not want to introduce random rem quotes into the CLASSPATH if "%CLASSPATH%" == "" goto emptyClasspath set "CLASSPATH=%CLASSPATH%;" :emptyClasspath set "CLASSPATH=%CLASSPATH%%CATALINA_HOME%\bin\bootstrap.jar" if not "%CATALINA_TMPDIR%" == "" goto gotTmpdir set "CATALINA_TMPDIR=%CATALINA_BASE%\temp" :gotTmpdir rem Add tomcat-juli.jar to classpath rem tomcat-juli.jar can be over-ridden per instance if not exist "%CATALINA_BASE%\bin\tomcat-juli.jar" goto juliClasspathHome set "CLASSPATH=%CLASSPATH%;%CATALINA_BASE%\bin\tomcat-juli.jar" goto juliClasspathDone :juliClasspathHome set "CLASSPATH=%CLASSPATH%;%CATALINA_HOME%\bin\tomcat-juli.jar" :juliClasspathDone if not "%LOGGING_CONFIG%" == "" goto noJuliConfig set LOGGING_CONFIG=-Dnop if not exist "%CATALINA_BASE%\conf\logging.properties" goto noJuliConfig set LOGGING_CONFIG=-Djava.util.logging.config.file="%CATALINA_BASE%\conf\logging.properties" :noJuliConfig set JAVA_OPTS=%JAVA_OPTS% %LOGGING_CONFIG% if not "%LOGGING_MANAGER%" == "" goto noJuliManager set LOGGING_MANAGER=-Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager :noJuliManager set JAVA_OPTS=%JAVA_OPTS% %LOGGING_MANAGER% rem ----- Execute The Requested Command --------------------------------------- echo Using CATALINA_BASE: "%CATALINA_BASE%" echo Using CATALINA_HOME: "%CATALINA_HOME%" echo Using CATALINA_TMPDIR: "%CATALINA_TMPDIR%" if ""%1"" == ""debug"" goto use_jdk echo Using JRE_HOME: "%JRE_HOME%" goto java_dir_displayed :use_jdk echo Using JAVA_HOME: "%JAVA_HOME%" :java_dir_displayed echo Using CLASSPATH: "%CLASSPATH%" set _EXECJAVA=%_RUNJAVA% set MAINCLASS=org.apache.catalina.startup.Bootstrap set ACTION=start set SECURITY_POLICY_FILE= set DEBUG_OPTS= set JPDA= if not ""%1"" == ""jpda"" goto noJpda set JPDA=jpda if not "%JPDA_TRANSPORT%" == "" goto gotJpdaTransport set JPDA_TRANSPORT=dt_socket :gotJpdaTransport if not "%JPDA_ADDRESS%" == "" goto gotJpdaAddress set JPDA_ADDRESS=8000 :gotJpdaAddress if not "%JPDA_SUSPEND%" == "" goto gotJpdaSuspend set JPDA_SUSPEND=n :gotJpdaSuspend if not "%JPDA_OPTS%" == "" goto gotJpdaOpts set JPDA_OPTS=-agentlib:jdwp=transport=%JPDA_TRANSPORT%,address=%JPDA_ADDRESS%,server=y,suspend=%JPDA_SUSPEND% :gotJpdaOpts shift :noJpda if ""%1"" == ""debug"" goto doDebug if ""%1"" == ""run"" goto doRun if ""%1"" == ""start"" goto doStart if ""%1"" == ""stop"" goto doStop if ""%1"" == ""configtest"" goto doConfigTest if ""%1"" == ""version"" goto doVersion echo Usage: catalina ( commands ... ) echo commands: echo debug Start Catalina in a debugger echo debug -security Debug Catalina with a security manager echo jpda start Start Catalina under JPDA debugger echo run Start Catalina in the current window echo run -security Start in the current window with security manager echo start Start Catalina in a separate window echo start -security Start in a separate window with security manager echo stop Stop Catalina echo configtest Run a basic syntax check on server.xml echo version What version of tomcat are you running? goto end :doDebug shift set _EXECJAVA=%_RUNJDB% set DEBUG_OPTS=-sourcepath "%CATALINA_HOME%\..\..\java" if not ""%1"" == ""-security"" goto execCmd shift echo Using Security Manager set "SECURITY_POLICY_FILE=%CATALINA_BASE%\conf\catalina.policy" goto execCmd :doRun shift if not ""%1"" == ""-security"" goto execCmd shift echo Using Security Manager set "SECURITY_POLICY_FILE=%CATALINA_BASE%\conf\catalina.policy" goto execCmd :doStart shift if not "%OS%" == "Windows_NT" goto noTitle if "%TITLE%" == "" set TITLE=Tomcat set _EXECJAVA=start "%TITLE%" %_RUNJAVA% goto gotTitle :noTitle set _EXECJAVA=start %_RUNJAVA% :gotTitle if not ""%1"" == ""-security"" goto execCmd shift echo Using Security Manager set "SECURITY_POLICY_FILE=%CATALINA_BASE%\conf\catalina.policy" goto execCmd :doStop shift set ACTION=stop set CATALINA_OPTS= goto execCmd :doConfigTest shift set ACTION=configtest set CATALINA_OPTS= goto execCmd :doVersion %_EXECJAVA% -classpath "%CATALINA_HOME%\lib\catalina.jar" org.apache.catalina.util.ServerInfo goto end :execCmd rem Get remaining unshifted command line arguments and save them in the set CMD_LINE_ARGS= :setArgs if ""%1""=="""" goto doneSetArgs set CMD_LINE_ARGS=%CMD_LINE_ARGS% %1 shift goto setArgs :doneSetArgs rem Execute Java with the applicable properties if not "%JPDA%" == "" goto doJpda if not "%SECURITY_POLICY_FILE%" == "" goto doSecurity %_EXECJAVA% %JAVA_OPTS% %CATALINA_OPTS% %DEBUG_OPTS% -Djava.endorsed.dirs="%JAVA_ENDORSED_DIRS%" -classpath "%CLASSPATH%" -Dcatalina.base="%CATALINA_BASE%" -Dcatalina.home="%CATALINA_HOME%" -Djava.io.tmpdir="%CATALINA_TMPDIR%" %MAINCLASS% %CMD_LINE_ARGS% %ACTION% goto end :doSecurity %_EXECJAVA% %JAVA_OPTS% %CATALINA_OPTS% %DEBUG_OPTS% -Djava.endorsed.dirs="%JAVA_ENDORSED_DIRS%" -classpath "%CLASSPATH%" -Djava.security.manager -Djava.security.policy=="%SECURITY_POLICY_FILE%" -Dcatalina.base="%CATALINA_BASE%" -Dcatalina.home="%CATALINA_HOME%" -Djava.io.tmpdir="%CATALINA_TMPDIR%" %MAINCLASS% %CMD_LINE_ARGS% %ACTION% goto end :doJpda if not "%SECURITY_POLICY_FILE%" == "" goto doSecurityJpda %_EXECJAVA% %JAVA_OPTS% %CATALINA_OPTS% %JPDA_OPTS% %DEBUG_OPTS% -Djava.endorsed.dirs="%JAVA_ENDORSED_DIRS%" -classpath "%CLASSPATH%" -Dcatalina.base="%CATALINA_BASE%" -Dcatalina.home="%CATALINA_HOME%" -Djava.io.tmpdir="%CATALINA_TMPDIR%" %MAINCLASS% %CMD_LINE_ARGS% %ACTION% goto end :doSecurityJpda %_EXECJAVA% %JAVA_OPTS% %CATALINA_OPTS% %JPDA_OPTS% %DEBUG_OPTS% -Djava.endorsed.dirs="%JAVA_ENDORSED_DIRS%" -classpath "%CLASSPATH%" -Djava.security.manager -Djava.security.policy=="%SECURITY_POLICY_FILE%" -Dcatalina.base="%CATALINA_BASE%" -Dcatalina.home="%CATALINA_HOME%" -Djava.io.tmpdir="%CATALINA_TMPDIR%" %MAINCLASS% %CMD_LINE_ARGS% %ACTION% goto end :end
1到99行一大堆注释说明就不看了，100到110行一堆run文件校验之类的一般用不到，直接跳到111行，接下来先删除上面可能产生的中间文件，接着按照正常流程，在上面的startup.bat文件中已经设置过CATALINA_HOME变量，并且校验了改变量下bin\catalina.bat文件已经存在（我猜作者写这一段是防止用户直接运行catalina.bat文件）。经过这些判断后跳转到128行，130到133行设置CATALINA_BASE变量，中间几行注释略过，139到144行如果有setenv.bat文件则执行一下该文件。147到153行执行setclasspath.bat文件（该文件在同级目录下已经提供，具体脚本下面已经贴出来了，可以读一下，这里不再做分析。主要功能校验是否设置JAVA_HOME变量，没有则在控制台显示出提示信息。注意该文件中第79行将会设置_RUNJAVA变量，该变量的值即JAVA_HOME或JRE_HOME的bin目录下的java.exe文件）。从156到224行校验并设置一堆变量（注意第202、203和204行，最后启动分析时将会用到）。226到231行将根据调用catalina.bat时设置的参数决定跳转，按照上一段的最后的说明，此时将会跳转到doStart标记行。从265行开始，校验和设置一些变量之后（注意第269行）将会跳转到execCmd标记行，即297行。297到305行作用是将系统参数保存到CMD_LINE_ARGS变量中。
接下来便是谜底解开的时候，正常情况下将会执行到310行，这里单独贴出来分析一下：
%_EXECJAVA% %JAVA_OPTS% %CATALINA_OPTS% %DEBUG_OPTS% -Djava.endorsed.dirs="%JAVA_ENDORSED_DIRS%" -classpath "%CLASSPATH%" -Dcatalina.base="%CATALINA_BASE%" -Dcatalina.home="%CATALINA_HOME%" -Djava.io.tmpdir="%CATALINA_TMPDIR%" %MAINCLASS% %CMD_LINE_ARGS% %ACTION%
按照202行的提示_EXECJAVA一开始的值等于_RUNJAVA，但在269行将该值改成了start "%TITLE%" %_RUNJAVA%，这里的作用是另启动一个命令行窗口，并给窗口起名，最终还是执行java.exe文件。从%JAVA_OPTS%开始到%MAINCLASS%之前都是在设置运行时参数和系统属性，%MAINCLASS%即203行的org.apache.catalina.startup.Bootstrap，后面是其它的命令行参数，最后一个参数%ACTION%在204行时被设置成start。归结起来一句话，即执行Bootstrap类的main方法。
setclasspath.bat:
@echo off rem Licensed to the Apache Software Foundation (ASF) under one or more rem contributor license agreements. See the NOTICE file distributed with rem this work for additional information regarding copyright ownership. rem The ASF licenses this file to You under the Apache License, Version 2.0 rem (the "License"); you may not use this file except in compliance with rem the License. You may obtain a copy of the License at rem rem http://www.apache.org/licenses/LICENSE-2.0 rem rem Unless required by applicable law or agreed to in writing, software rem distributed under the License is distributed on an "AS IS" BASIS, rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. rem See the License for the specific language governing permissions and rem limitations under the License. rem --------------------------------------------------------------------------- rem Set JAVA_HOME or JRE_HOME if not already set, ensure any provided settings rem are valid and consistent with the selected start-up options and set up the rem endorsed directory. rem rem $Id: setclasspath.bat 1202062 2011-11-15 06:50:02Z mturk $ rem --------------------------------------------------------------------------- rem Make sure prerequisite environment variables are set rem In debug mode we need a real JDK (JAVA_HOME) if ""%1"" == ""debug"" goto needJavaHome rem Otherwise either JRE or JDK are fine if not "%JRE_HOME%" == "" goto gotJreHome if not "%JAVA_HOME%" == "" goto gotJavaHome 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 :needJavaHome rem Check if we have a usable JDK if "%JAVA_HOME%" == "" goto noJavaHome if not exist "%JAVA_HOME%\bin\java.exe" goto noJavaHome if not exist "%JAVA_HOME%\bin\javaw.exe" goto noJavaHome if not exist "%JAVA_HOME%\bin\jdb.exe" goto noJavaHome if not exist "%JAVA_HOME%\bin\javac.exe" goto noJavaHome set "JRE_HOME=%JAVA_HOME%" goto okJava :noJavaHome echo The JAVA_HOME environment variable is not defined correctly. echo It is needed to run this program in debug mode. echo NB: JAVA_HOME should point to a JDK not a JRE. goto exit :gotJavaHome rem No JRE given, use JAVA_HOME as JRE_HOME set "JRE_HOME=%JAVA_HOME%" :gotJreHome rem Check if we have a usable JRE if not exist "%JRE_HOME%\bin\java.exe" goto noJreHome if not exist "%JRE_HOME%\bin\javaw.exe" goto noJreHome goto okJava :noJreHome rem Needed at least a JRE echo The JRE_HOME environment variable is not defined correctly echo This environment variable is needed to run this program goto exit :okJava rem Don't override the endorsed dir if the user has set it previously if not "%JAVA_ENDORSED_DIRS%" == "" goto gotEndorseddir rem Set the default -Djava.endorsed.dirs argument set "JAVA_ENDORSED_DIRS=%CATALINA_HOME%\endorsed" :gotEndorseddir rem Set standard command for invoking Java. rem Note that NT requires a window name argument when using start. rem Also note the quoting as JAVA_HOME may contain spaces. set _RUNJAVA="%JRE_HOME%\bin\java" set _RUNJDB="%JAVA_HOME%\bin\jdb" goto end :exit exit /b 1 :end exit /b 0
三、总结
以上即tomcat的启动脚本中的总体流程，只是讲了默认的脚本运行方式，但在脚本阅读中可以看到能根据catalina.bat里可以根据不同参数以不同方式运行tomcat：
debug Start Catalina in a debugger
debug -security Debug Catalina with a security manager
jpda start Start Catalina under JPDA debugger
run Start Catalina in the current window
run -security Start in the current window with security manager
start Start Catalina in a separate window
start -security Start in a separate window with security manager
stop Stop Catalina
configtest Run a basic syntax check on server.xml
只要能看懂基本dos命令，这几个脚本的阅读其实很简单，其他bat文件可以大体浏览一下，会发现转了半天，最终都会执行catalina.bat文件，而catalina.bat文件里最终会执行Bootstrap文件的main方法，不同的是调用main方法时会各自添加不同的入参而已。bat文件用于windows操作系统下启动tomcat，而sh文件则用于unix环境下的启动，原理是一致的。