Parse the Tomcat startup script startup.bat

An overview of the

We usually use startup. bat in Tomcat to start Tomcat. But what does this do?

You all know that if an Java program needs to be started, it definitely needs the main method, so where is the main method?

What parameters are configured in the Tomcat script, and when will Tomcat fail to start?

Let's take a look at Tomcat's three most important startup scripts with a list of questions:

startup.bat catalina.bat setclasspath.bat

startup bat script

The script does the following things:

Set the value of the CATALINA_HOME environment variable Find the catalina.bat script Call the catalina.bat script and pass the arguments

Post the content of the simplified version of the startup.bat script

@echo off
rem  After executing this command ,  Environment variables are added or changed only if they match to  endlocal  Command or go to the end of the file .
setlocal
rem  Assuming that  CATALINA_HOME  Environment variables are not defined 
rem  Takes the path value of the current directory ,  Assigned to  CURRENT_DIR  variable ,  is  ./apache-tomcat-x.x.xx/bin
set "CURRENT_DIR=%cd%"
rem  if  CATALINA_HOME  The variable value is not  ""  if ,  Transferred to the  gotHome  Labels place 
if not "%CATALINA_HOME%" == "" goto gotHome
rem  if  CATALINA_HOME  is  ""  if ,  Set up the  CATALINA_HOME  A variable's value to   The path value of the current directory (./apache-tomcat-x.x.xx/bin)
set "CATALINA_HOME=%CURRENT_DIR%"
rem  Determine if there are any in the current path  bin\catalina.bat,  That is  ./apache-tomcat-x.x.xx/bin/bin/catalina.bat
rem  If it exists ,  Directly transferred to the  okHome  Labels place ,  Obviously it doesn't exist 
if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome
rem  If it doesn't exist , CATALINA_HOME  Takes the value of the parent directory ,  That is (./apache-tomcat-x.x.xx/)
cd ..
set "CATALINA_HOME=%cd%"
rem  Enter the  CURRENT_DIR(./apache-tomcat-x.x.xx/bin)
cd "%CURRENT_DIR%"
:gotHome
rem  Go through the Settings above , CATALINA_HOME  The value of theta is already zero : ./apache-tomcat-x.x.xx/
rem  So the collation can be found  catalina.bat  The script ,  Directly transferred to the  okHome  Labels place 
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  Set up the  EXECUTABLE  The variable points to  catalina.bat  The script 
set "EXECUTABLE=%CATALINA_HOME%\bin\catalina.bat"
rem  Check the target executable (catalina.bat) If there is a ,  Usually it does ,  Directly transferred to the  okExec  Labels place 
rem  If it doesn't exist ,  Directly out of .  Start the  Tomcat  The end of the 
if exist "%EXECUTABLE%" goto okExec
echo Cannot find "%EXECUTABLE%"
echo This file is needed to run this program
goto end
:okExec
rem  It's no use getting the rest  shift  The command line argument that is fetched ,  And save them in  CMD_LINE_ARGS
set CMD_LINE_ARGS=
:setArgs
rem  If the first 1 Three command line arguments are empty ,  Jump to the  doneSetArgs  Labels place 
rem "%1" :  Represents the first after the execution of the command 1 A parameter 
if ""%1""=="""" goto doneSetArgs
rem  The first 1 If the parameter is not empty ,  Joining together to  CMD_LINE_ARGS  variable 
set CMD_LINE_ARGS=%CMD_LINE_ARGS% %1
rem  This command can be baidu 
shift
goto setArgs
:doneSetArgs
rem  It's set up  EXECUTABLE  The value of the variable is pointing  catalina.bat  The script ,  The use of  call  Command execution call ,  And pass in the parameters 
rem  The following ,  Let's see  catalina.bat  Script content 
rem  Complete command : ./apache-tomcat-x.x.xx/bin/catalina.bat start
call "%EXECUTABLE%" start %CMD_LINE_ARGS%
:end

To understand some of the commands in the script, take a look at the following common commands (Window we used)

rem: the code after this command will not be executed, equivalent to a comment echo off: turn off the display of commands. If not set, any commands executed will be displayed echo: outputs what follows setlocal: after executing this command, the scope of environment variables added or changed is limited to matching the endlocal command or reaching the end of the file. set: sets 1 variable :xxx: define 1 tag goto: jump to the designated label call: execute the command

Let's take a one-line look at the startup.bat script

set "CURRENT_DIR=%cd%"

%cd% : represents the path to the directory where the file is located

If we extracted Tomcat directory for D: / apache - tomcat - x. x. x /. Because startup. bat command in bin directory, so the % % cd said directory is D: / apache - tomcat - x. x. x/bin

if not "%CATALINA_HOME%" == "" goto gotHome

We don't normally configure the CATALINA_HOME environment variable, so we won't go to the gotHome TAB.

set "CATALINA_HOME=%CURRENT_DIR%"

Directly assume the current directory to be the value of CATALINA_HOME

if exist "%CATALINA_HOME%\bin\catalina.bat" goto okHome

Then fixed format to determine whether one have catalina bat script, of course, this is will not exist, because CATALINA_HOME = D: / apache - tomcat - x. x. x/bin

cd ..
set "CATALINA_HOME=%cd%"

Because the Tomcat directory format is fixed, here you go directly to the parent directory (cd..) , and then set the value of CATALINA_HOME to the parent directory (D:/ apache-tomcat-x.x.x).

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

If we unzip Tomcat and put startup.bat in the bin directory that is not Tomcat, we can't find it here, so we can directly goto end and exit the startup of Tomcat.

Ok, so here we go straight to the okHome TAB.

:okHome
set "EXECUTABLE=%CATALINA_HOME%\bin\catalina.bat"

Ok, it's easy to set the value of the 1 EXECUTABLE variable to point to the catalina.bat script.

if exist "%EXECUTABLE%" goto okExec
echo Cannot find "%EXECUTABLE%"
echo This file is needed to run this program
goto end

Once again, I checked whether this script exists or not. If it does, I will directly transfer it to the okExec label and it can be executed.

If it does not pass the check, exit the boot and print an error message.

:okExec
set CMD_LINE_ARGS=
:setArgs
if ""%1""=="""" goto doneSetArgs
set CMD_LINE_ARGS=%CMD_LINE_ARGS% %1
shift
goto setArgs

A variable CMD_LINE_ARGS is set, and its value is temporarily empty

There appeared a "" % 1" = = "" "" "", open it to see is whether" % 1 "is equal to". "well, what does" % 1 "is the & # 63;

This is a syntax for the window batch, which is the first argument after the command is executed. For this case, we did not pass any arguments, so the '%1' is' "(empty).

Jump directly to the doneSetArgs label.

If it's not empty, put it in the back.

The shift command in this case means to remove one parameter. For example:

@echo off
echo "%1"
shift
echo "%1"

Build an test.bat batch, copy the above code in, execute it in cmd and give it two parameters

Here is the result of the execution, where you can remove @echo off and execute it to verify that the command 1 is working

PS D:\> .\test Hello World
"Hello"
"World"
PS D:\>

So that should make sense to you.

Continue to analyze

:doneSetArgs
call "%EXECUTABLE%" start %CMD_LINE_ARGS%
:end

EXECUTABLE = %CATALINA_HOME%\bin\ catalina.bat is set above, so the script catalina.bat is actually called, and an start parameter is passed to it.

If we run startup.bat in cmd and we have a parameter of 1, then 1 is passed.

This is actually done: %CATALINA_HOME%\bin\ catalina.bat start

conclusion

The purpose of this script is to find catalina.bat and call it.

The above is the whole content of this article, I hope the content of this article can bring you a certain help in your study or work, the next article will continue to introduce Tomcat related knowledge -- "parsing Tomcat's startup script --catalina.bat", interested friends can read it