[MNG-7195] Rework JAVA_HOME handling

Dramatically simplify/rework handling by leaving setting JAVA_HOME to
the user and try to load java(1) command from it. Technically Maven itself does
not require JAVA_HOME to be set. If not set, use java(1) command from
PATH on both Windows and POSIX-like systems.

This closes #514

apache-maven/src/assembly/maven/bin/mvnDebug

@@ -22,7 +22,7 @@
 #
 # Environment Variable Prerequisites
 #
-#   JAVA_HOME           Must point at your Java Development Kit installation.
+#   JAVA_HOME           (Optional) Points to a Java installation.
 #   MAVEN_OPTS          (Optional) Java runtime options used when Maven is executed.
 #   MAVEN_SKIP_RC       (Optional) Flag to disable loading of mavenrc files.
 #   MAVEN_DEBUG_ADDRESS (Optional) Set the debug address. Default value is localhost:8000

apache-maven/src/assembly/maven/bin/mvnDebug.cmd

@@ -20,7 +20,7 @@
 @REM
 @REM Environment Variable Prerequisites
 @REM
-@REM   JAVA_HOME           Must point at your Java Development Kit installation.
+@REM   JAVA_HOME           (Optional) Points to a Java installation.
 @REM   MAVEN_BATCH_ECHO    (Optional) Set to 'on' to enable the echoing of the batch commands.
 @REM   MAVEN_BATCH_PAUSE   (Optional) set to 'on' to wait for a key stroke before ending.
 @REM   MAVEN_OPTS          (Optional) Java runtime options used when Maven is executed.
@@ -37,7 +37,7 @@ title %0
 
 @setlocal
 
-IF "%MAVEN_DEBUG_ADDRESS%"=="" @set MAVEN_DEBUG_ADDRESS=localhost:8000
+if "%MAVEN_DEBUG_ADDRESS%"=="" @set MAVEN_DEBUG_ADDRESS=localhost:8000
 
 @set MAVEN_DEBUG_OPTS=-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=y,address=%MAVEN_DEBUG_ADDRESS%
 

apache-maven/src/assembly/shared/init

@@ -16,47 +16,26 @@ if $mingw ; then
     JAVA_HOME=`(cd "$JAVA_HOME"; pwd)`
 fi
 
-if [ -z "$JAVA_HOME" ]; then
-  javaExecutable="`which javac`"
-  if [ -n "$javaExecutable" ] && ! [ "`expr \"$javaExecutable\" : '\([^ ]*\)'`" = "no" ]; then
-    # readlink(1) is not available as standard on Solaris 10.
-    readLink=`which readlink`
-    if [ ! `expr "$readLink" : '\([^ ]*\)'` = "no" ]; then
-      if $darwin ; then
-        javaHome="`dirname \"$javaExecutable\"`"
-        javaExecutable="`cd \"$javaHome\" && pwd -P`/javac"
-      else
-        javaExecutable="`readlink -f \"$javaExecutable\"`"
-      fi
-      javaHome="`dirname \"$javaExecutable\"`"
-      javaHome=`expr "$javaHome" : '\(.*\)/bin'`
-      JAVA_HOME="$javaHome"
-      export JAVA_HOME
-    fi
-  fi
-fi
-
-if [ -z "$JAVACMD" ] ; then
-  if [ -n "$JAVA_HOME"  ] ; then
-    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
-      # IBM's JDK on AIX uses strange locations for the executables
-      JAVACMD="$JAVA_HOME/jre/sh/java"
-    else
-      JAVACMD="$JAVA_HOME/bin/java"
-    fi
+if [ -n "$JAVA_HOME" ] ; then
+  if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+    # IBM's JDK on AIX uses strange locations for the executables
+    JAVACMD="$JAVA_HOME/jre/sh/java"
   else
-    JAVACMD="`which java`"
+    JAVACMD="$JAVA_HOME/bin/java"
+
+    if [ ! -x "$JAVACMD" ] ; then
+      echo "The JAVA_HOME environment variable is not defined correctly, so Apache Maven cannot be started." >&2
+      echo "JAVA_HOME is set to \"$JAVA_HOME\", but \"\$JAVA_HOME/bin/java\" does not exist." >&2
+      exit 1
+    fi
   fi
-fi
+else
+  JAVACMD="`which java`"
 
-if [ ! -x "$JAVACMD" ] ; then
-  echo "The JAVA_HOME environment variable is not defined correctly," >&2
-  echo "this environment variable is needed to run this program." >&2
-  exit 1
-fi
-
-if [ -z "$JAVA_HOME" ] ; then
-  echo "Warning: JAVA_HOME environment variable is not set." >&2
+  if [ ! -x "$JAVACMD" ] ; then
+    echo "The java(1) command does not exist in PATH nor is JAVA_HOME set, so Apache Maven cannot be started." >&2
+    exit 1
+  fi
 fi
 
 # traverses directory structure from process work directory to filesystem root

apache-maven/src/assembly/shared/validate

@@ -22,7 +22,7 @@
 #
 # Environment Variable Prerequisites
 #
-#   JAVA_HOME       Must point at your Java Development Kit installation.
+#   JAVA_HOME       (Optional) Points to a Java installation.
 #   MAVEN_OPTS      (Optional) Java runtime options used when Maven is executed.
 #   MAVEN_SKIP_RC   (Optional) Flag to disable loading of mavenrc files.
 # -----------------------------------------------------------------------------
@@ -46,26 +46,9 @@ fi
 # OS specific support. $var _must_ be set to either true or false.
 cygwin=false;
 mingw=false;
-darwin=false;
 case "`uname`" in
   CYGWIN*) cygwin=true;;
   MINGW*) mingw=true;;
-  Darwin*) darwin=true
-    # Use /usr/libexec/java_home if available, otherwise fall back to /Library/Java/Home
-    # See https://developer.apple.com/library/mac/qa/qa1170/_index.html
-    if [ -z "$JAVA_HOME" ]; then
-      if [ -x "/usr/libexec/java_home" ]; then
-        export JAVA_HOME="`/usr/libexec/java_home`"
-      else
-        export JAVA_HOME="/Library/Java/Home"
-      fi
-    fi
-    ;;
 esac
 
-if [ -z "$JAVA_HOME" ] ; then
-  if [ -r /etc/gentoo-release ] ; then
-    JAVA_HOME=`java-config --jre-home`
-  fi
-fi
 

apache-maven/src/assembly/shared/validate.cmd

@@ -20,7 +20,7 @@
 @REM
 @REM Environment Variable Prerequisites
 @REM
-@REM   JAVA_HOME          Must point at your Java Development Kit installation.
+@REM   JAVA_HOME         (Optional) Points to a Java installation.
 @REM   MAVEN_BATCH_ECHO  (Optional) Set to 'on' to enable the echoing of the batch commands.
 @REM   MAVEN_BATCH_PAUSE (Optional) set to 'on' to wait for a key stroke before ending.
 @REM   MAVEN_OPTS        (Optional) Java runtime options used when Maven is executed.
@@ -46,20 +46,21 @@ if exist "%USERPROFILE%\mavenrc_pre.cmd" call "%USERPROFILE%\mavenrc_pre.cmd" %*
 set ERROR_CODE=0
 
 @REM ==== START VALIDATION ====
-if not "%JAVA_HOME%"=="" goto OkJHome
+if not "%JAVA_HOME%"=="" goto javaHomeSet
 for %%i in (java.exe) do set "JAVACMD=%%~$PATH:i"
-goto checkJCmd
+goto checkJavaCmd
 
-:OkJHome
+:javaHomeSet
 set "JAVACMD=%JAVA_HOME%\bin\java.exe"
 
-:checkJCmd
 if not exist "%JAVACMD%" (
-  echo The JAVA_HOME environment variable is not defined correctly, >&2
-  echo this environment variable is needed to run this program. >&2
+  echo The JAVA_HOME environment variable is not defined correctly, so Apache Maven cannot be started. >&2
+  echo JAVA_HOME is set to "%JAVA_HOME%", but "%%JAVA_HOME%%\bin\java.exe" does not exist. >&2
   goto error
 )
 
-if "%JAVA_HOME%"=="" (
-  echo Warning: JAVA_HOME environment variable is not set. >&2
+:checkJavaCmd
+if not exist "%JAVACMD%" (
+  echo The java.exe command does not exist in PATH nor is JAVA_HOME set, so Apache Maven cannot be started. >&2
+  goto error
 )