maven源码分析- mvn.bat分析

第一次知道MAVEN是在2008年，当时想分析geoserver这个开源项目，发现该项目采用了maven进行项目管理，当时粗略的学习了一下。真正在工作中使用是在09年下半年，个人感觉使用起来还是非常好，特别是在jar包的管理上规范了很多，而且项目中添加jar包或下源码都十分方便，但是团队中的成员总是有个别人使用得很痛苦，不是这个找不到，就是发布项目出问题，鉴于此，我动了分析源码的念头。

先通过svn从 https://svn.apache.org/repos/asf/maven/maven-3/trunk 上checkout了一份源码。项目结构如下图：

由于使用maven基本是通过其bin目录下的mvn.bat命令为入口，所以有必要先了解下该批处理文件，把多余的注释去掉后，该文件显示如下：

  1 @echo off
  2 @REM enable echoing my setting MAVEN_BATCH_ECHO to 'on'
  3 @if "%MAVEN_BATCH_ECHO%" == "on"  echo %MAVEN_BATCH_ECHO%
  4
  5 @REM set %HOME% to equivalent of $HOME
  6 if "%HOME%" == "" (set "HOME=%HOMEDRIVE%%HOMEPATH%")
  7
  8 @REM Execute a user defined script before this one
  9 if not "%MAVEN_SKIP_RC%" == "" goto skipRcPre
 10 if exist "%HOME%\mavenrc_pre.bat" call "%HOME%\mavenrc_pre.bat"
 11 :skipRcPre
 12
 13 set ERROR_CODE=0
 14
 15 @REM set local scope for the variables with windows NT shell
 16 if "%OS%"=="Windows_NT" @setlocal
 17 if "%OS%"=="WINNT" @setlocal
 18
 19 @REM ==== START VALIDATION ====
 20 if not "%JAVA_HOME%" == "" goto OkJHome
 21
 22 echo.
 23 echo ERROR: JAVA_HOME not found in your environment.
 24 echo Please set the JAVA_HOME variable in your environment to match the
 25 echo location of your Java installation
 26 echo.
 27 goto error
 28
 29 :OkJHome
 30 if exist "%JAVA_HOME%\bin\java.exe" goto chkMHome
 31
 32 echo.
 33 echo ERROR: JAVA_HOME is set to an invalid directory.
 34 echo JAVA_HOME = "%JAVA_HOME%"
 35 echo Please set the JAVA_HOME variable in your environment to match the
 36 echo location of your Java installation
 37 echo.
 38 goto error
 39
 40 :chkMHome
 41 if not "%M2_HOME%"=="" goto valMHome
 42
 43 if "%OS%"=="Windows_NT" SET "M2_HOME=%~dp0.."
 44 if "%OS%"=="WINNT" SET "M2_HOME=%~dp0.."
 45 if not "%M2_HOME%"=="" goto valMHome
 46
 47 echo.
 48 echo ERROR: M2_HOME not found in your environment.
 49 echo Please set the M2_HOME variable in your environment to match the
 50 echo location of the Maven installation
 51 echo.
 52 goto error
 53
 54 :valMHome
 55
 56 :stripMHome
 57 if not "_%M2_HOME:~-1%"=="_\" goto checkMBat
 58 set "M2_HOME=%M2_HOME:~0,-1%"
 59 goto stripMHome
 60
 61 :checkMBat
 62 if exist "%M2_HOME%\bin\mvn.bat" goto init
 63
 64 echo.
 65 echo ERROR: M2_HOME is set to an invalid directory.
 66 echo M2_HOME = "%M2_HOME%"
 67 echo Please set the M2_HOME variable in your environment to match the
 68 echo location of the Maven installation
 69 echo.
 70 goto error
 71 @REM ==== END VALIDATION ====
 72
 73 :init
 74 @REM Decide how to startup depending on the version of windows
 75
 76 @REM -- Windows NT with Novell Login
 77 if "%OS%"=="WINNT" goto WinNTNovell
 78
 79 @REM -- Win98ME
 80 if NOT "%OS%"=="Windows_NT" goto Win9xArg
 81
 82 :WinNTNovell
 83
 84 @REM -- 4NT shell
 85 if "%@eval[2+2]" == "4" goto 4NTArgs
 86
 87 @REM -- Regular WinNT shell
 88 set MAVEN_CMD_LINE_ARGS=%*
 89 goto endInit
 90
 91 @REM The 4NT Shell from jp software
 92 :4NTArgs
 93 set MAVEN_CMD_LINE_ARGS=%$
 94 goto endInit
 95
 96 :Win9xArg
 97 @REM Slurp the command line arguments.  This loop allows for an unlimited number
 98 @REM of agruments (up to the command line limit, anyway).
 99 set MAVEN_CMD_LINE_ARGS=
100 :Win9xApp
101 if %1a==a goto endInit
102 set MAVEN_CMD_LINE_ARGS=%MAVEN_CMD_LINE_ARGS% %1
103 shift
104 goto Win9xApp
105
106 @REM Reaching here means variables are defined and arguments have been captured
107 :endInit
108 SET MAVEN_JAVA_EXE="%JAVA_HOME%\bin\java.exe"
109
110 @REM -- 4NT shell
111 if "%@eval[2+2]" == "4" goto 4NTCWJars
112
113 @REM -- Regular WinNT shell
114 for %%i in ("%M2_HOME%"\boot\plexus-classworlds-*) do set CLASSWORLDS_JAR="%%i"
115 goto runm2
116
117 @REM The 4NT Shell from jp software
118 :4NTCWJars
119 for %%i in ("%M2_HOME%\boot\plexus-classworlds-*") do set CLASSWORLDS_JAR="%%i"
120 goto runm2
121
122 @REM Start MAVEN2
123 :runm2
124 set CLASSWORLDS_LAUNCHER=org.codehaus.plexus.classworlds.launcher.Launcher
125 %MAVEN_JAVA_EXE% %MAVEN_OPTS% -classpath %CLASSWORLDS_JAR% "-Dclassworlds.conf=%M2_HOME%\bin\m2.conf" "-Dmaven.home=%M2_HOME%" %CLASSWORLDS_LAUNCHER% %MAVEN_CMD_LINE_ARGS%
126 if ERRORLEVEL 1 goto error
127 goto end
128
129 :error
130 if "%OS%"=="Windows_NT" @endlocal
131 if "%OS%"=="WINNT" @endlocal
132 set ERROR_CODE=1
133
134 :end
135 @REM set local scope for the variables with windows NT shell
136 if "%OS%"=="Windows_NT" goto endNT
137 if "%OS%"=="WINNT" goto endNT
138
139 @REM For old DOS remove the set variables from ENV - we assume they were not set
140 @REM before we started - at least we don't leave any baggage around
141 set MAVEN_JAVA_EXE=
142 set MAVEN_CMD_LINE_ARGS=
143 goto postExec
144
145 :endNT
146 @endlocal & set ERROR_CODE=%ERROR_CODE%
147
148 :postExec
149
150 if not "%MAVEN_SKIP_RC%" == "" goto skipRcPost
151 if exist "%HOME%\mavenrc_post.bat" call "%HOME%\mavenrc_post.bat"
152 :skipRcPost
153
154 @REM pause the batch file if MAVEN_BATCH_PAUSE is set to 'on'
155 if "%MAVEN_BATCH_PAUSE%" == "on" pause
156
157 if "%MAVEN_TERMINATE_CMD%" == "on" exit %ERROR_CODE%
158
159 cmd /C exit /B %ERROR_CODE%

下面对上述批处理文件展开详细分析，首先需要把一些批处理常用命令讲解一下：

(1) @  符号的作用是命令行回显屏蔽符,可以在其他批处理命令前加@符来控制该命令是否回显在控制台窗口

比如批处理中REM与@REM的区别:

REM是批处理中的注释命令,@REM的作用与REM相同，只不过在回显上有差别，如果echo off，@要与否是无所谓的.但是，如果echo on，在运行的时

候，不带@的行的DOS命令都会被回显，包括注释

(2) %HOMEDRIVE%和%HOMEPATH%

%homedrive%指操作系统所在的盘，如装在C盘，则为c:\

%HOMEPATH%指登录当前操作系统的用户的用户目录，如登录用户为administrator, 则一般为\Documents and Settings\administrator

(3) ~ 波浪号的作用是截取字符串

如:  假设set str=123456789

则 %str:~0,1% 表示要从字符串的第0位直到截取字符串最左边一个字符后的位置。截取结果为1

%str:~0,-1%表示要从字符串的第0位直到截取字符串最右边一个字符后的位置。截取结是为12345678

(4) %~dp0  : 获取当前批处理的运行目录路径

(5) setlocal ：启动批处理文件中环境变量的本地化,和endlocal配套使用，使得某些变量的变化只是维持在setlocal和endlocal之间 ,如：

set var=123     setlocal        set var=abcd     endlocal     echo %var%

当echo时，var变量应为123

(6) %[1-9]表示参数，参数是指在运行批处理文件时在文件名后加的以空格（或者Tab）分隔的字符串。变量可以从%0到%9，%0表示批处理命令本身，其它参

数字符串用%1到%9顺序表示。

(7) shift ,  去掉第一个参数，后面的参数依次向前移

[本文转载自胡欣老师]