1. mac 下面是用homebrew 安裝maven，安裝成功，設置完M2_HOME ,使用mvn －version進行檢測
houenxundeMacBook-Pro:3.3.9 houenxun$ mvn －version 錯誤: 找不到或無法加載主類 org.codehaus.plexus.classworlds.launcher.Launcher
2. 網上看了一堆解決方案，不明所以，於是自己嘗試解決，首先，先定位一下問題的腳本
houenxundeMacBook-Pro:3.3.9 houenxun$ which mvn /usr/local/bin/mvn houenxundeMacBook-Pro:3.3.9 houenxun$ ls -l /usr/local/bin/mvn lrwxr-xr-x 1 houenxun admin 29 4 7 15:52 /usr/local/bin/mvn -> ../Cellar/maven/3.3.9/bin/mvn
打開mvn文件
#!/bin/bash
JAVA_HOME="${JAVA_HOME:-$(/usr/libexec/java_home)}" exec "/usr/local/Cellar/maven/3.3.9/libexec/bin/mvn" "$@"可以看到真正調用的是
/usr/local/Cellar/maven/3.3.9/libexec/bin/mvn
打開該文件,文件比較長，定位到最後報錯的地方
exec "$JAVACMD" \
$MAVEN_OPTS \
$MAVEN_DEBUG_OPTS \
-classpath "${M2_HOME}"/boot/plexus-classworlds-*.jar \
"-Dclassworlds.conf=${M2_HOME}/bin/m2.conf" \
"-Dmaven.home=${M2_HOME}" "-Dmaven.multiModuleProjectDirectory=${MAVEN_PROJECTBASEDIR}" \
${CLASSWORLDS_LAUNCHER} "$@"使用echo打印真正的語句
exec /Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/bin/java -classpath /usr/local/Cellar/maven/3.3.9/boot/plexus-classworlds-*.jar -Dclassworlds.conf=/usr/local/Cellar/maven/3.3.9/bin/m2.conf -Dmaven.home=/usr/local/Cellar/maven/3.3.9 -Dmaven.multiModuleProjectDirectory=/usr/local/Cellar/maven/3.3.9/libexec/bin org.codehaus.plexus.classworlds.launcher.Launcher
3. 很奇怪，在/usr/local/Cellar/maven/3.3.9目錄下boot和bin都是不存在的，而卻存在/usr/local/Cellar/maven/3.3.9/libexec目錄下
houenxundeMacBook-Pro:3.3.9 houenxun$ pwd /usr/local/Cellar/maven/3.3.9 houenxundeMacBook-Pro:3.3.9 houenxun$ ls INSTALL_RECEIPT.json NOTICE bin LICENSE README.txt libexec houenxundeMacBook-Pro:3.3.9 houenxun$ houenxundeMacBook-Pro:3.3.9 houenxun$ cd libexec/ houenxundeMacBook-Pro:libexec houenxun$ ls bin boot conf lib houenxundeMacBook-Pro:libexec houenxun$
4. 嘗試將他們拷貝出去，的確OK了
houenxundeMacBook-Pro:3.3.9 houenxun$ mvn -version exec /Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/bin/java -classpath /usr/local/Cellar/maven/3.3.9/boot/plexus-classworlds-2.5.2.jar -Dclassworlds.conf=/usr/local/Cellar/maven/3.3.9/bin/m2.conf -Dmaven.home=/usr/local/Cellar/maven/3.3.9 -Dmaven.multiModuleProjectDirectory=/usr/local/Cellar/maven/3.3.9 org.codehaus.plexus.classworlds.launcher.Launcher -version Apache Maven 3.3.9 (bb52d8502b132ec0a5a3f4c09453c07478323dc5; 2015-11-11T00:41:47+08:00) Maven home: /usr/local/Cellar/maven/3.3.9 Java version: 1.8.0_77, vendor: Oracle Corporation Java home: /Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/jre Default locale: zh_CN, platform encoding: UTF-8 OS name: "mac os x", version: "10.11.4", arch: "x86_64", family: "mac"
5. 問題似乎解決了，但不禁奇怪，難道homebrew安裝maven有bug？？？
我習慣性的設置M2_HOME,爲啥要設置，是要把maven的目錄設置成執行環節目錄，但根據第二步驟
/usr/bin/mvn是mvn命令的符號鏈接，有了這個符號鏈接M2_HOME也就不起作用了。我們嘗試禁用M2_HOME環境變量
houenxundeMacBook-Pro:~ houenxun$ mvn -version exec /Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/bin/java -classpath /usr/local/Cellar/maven/3.3.9/libexec/boot/plexus-classworlds-2.5.2.jar -Dclassworlds.conf=/usr/local/Cellar/maven/3.3.9/libexec/bin/m2.conf -Dmaven.home=/usr/local/Cellar/maven/3.3.9/libexec -Dmaven.multiModuleProjectDirectory=/Users/houenxun org.codehaus.plexus.classworlds.launcher.Launcher -version Apache Maven 3.3.9 (bb52d8502b132ec0a5a3f4c09453c07478323dc5; 2015-11-11T00:41:47+08:00) Maven home: /usr/local/Cellar/maven/3.3.9/libexec Java version: 1.8.0_77, vendor: Oracle Corporation Java home: /Library/Java/JavaVirtualMachines/jdk1.8.0_77.jdk/Contents/Home/jre Default locale: zh_CN, platform encoding: UTF-8 OS name: "mac os x", version: "10.11.4", arch: "x86_64", family: "mac"
依然可以執行，而且boot和lib的路徑也發生變化了！
原來新版本的maven已經不需要配置M2_HOME 環境變量，並且目錄層次結構也發生了變化，但是爲了兼容原來的老版本，腳本中通過M2_HOME來選擇新舊目錄層次，哎，自己畫蛇添足了！！！