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maven源码分析- mvn.bat分析
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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]
