Use java from path if JAVA_HOME is not set

This commit adds support to the Windows scripts for finding java.exe via
the path if JAVA_HOME is not set.

Relates #18685

distribution/src/main/resources/bin/elasticsearch-plugin.bat

@@ -2,7 +2,15 @@
 
 SETLOCAL enabledelayedexpansion
 
-if NOT DEFINED JAVA_HOME goto err
+IF DEFINED JAVA_HOME (
+  set JAVA=%JAVA_HOME%\bin\java.exe
+) ELSE (
+  FOR %%I IN (java.exe) DO set JAVA=%%~$PATH:I
+)
+IF NOT EXIST "%JAVA%" (
+  ECHO Could not find any executable java binary. Please install java in your PATH or set JAVA_HOME 1>&2
+  EXIT /B 1
+)
 
 set SCRIPT_DIR=%~dp0
 for %%I in ("%SCRIPT_DIR%..") do set ES_HOME=%%~dpfI
@@ -48,15 +56,6 @@ GOTO loop
 
 SET HOSTNAME=%COMPUTERNAME%
 
-"%JAVA_HOME%\bin\java" %ES_JAVA_OPTS% -Des.path.home="%ES_HOME%" !properties! -cp "%ES_HOME%/lib/*;" "org.elasticsearch.plugins.PluginCli" !args!
-goto finally
-
-
-:err
-echo JAVA_HOME environment variable must be set!
-pause
-
-
-:finally
+"%JAVA%" %ES_JAVA_OPTS% -Des.path.home="%ES_HOME%" !properties! -cp "%ES_HOME%/lib/*;" "org.elasticsearch.plugins.PluginCli" !args!
 
 ENDLOCAL

distribution/src/main/resources/bin/elasticsearch.bat

@@ -35,14 +35,14 @@ FOR /F "usebackq tokens=1* delims= " %%A IN (!params!) DO (
     SET current=%%A
     SET params='%%B'
 	SET silent=N
-	
+
 	IF "!current!" == "-s" (
 		SET silent=Y
 	)
 	IF "!current!" == "--silent" (
 		SET silent=Y
-	)	
-	
+	)
+
 	IF "!silent!" == "Y" (
 		SET nopauseonerror=Y
 	) ELSE (
@@ -52,7 +52,7 @@ FOR /F "usebackq tokens=1* delims= " %%A IN (!params!) DO (
             SET newparams=!current!
         )
 	)
-	
+
     IF "x!params!" NEQ "x" (
 		GOTO loop
 	)
@@ -79,6 +79,6 @@ IF ERRORLEVEL 1 (
 	EXIT /B %ERRORLEVEL%
 )
 
-"%JAVA_HOME%\bin\java" %ES_JAVA_OPTS% %ES_PARAMS% -cp "%ES_CLASSPATH%" "org.elasticsearch.bootstrap.Elasticsearch" !newparams!
+"%JAVA%" %ES_JAVA_OPTS% %ES_PARAMS% -cp "%ES_CLASSPATH%" "org.elasticsearch.bootstrap.Elasticsearch" !newparams!
 
 ENDLOCAL

distribution/src/main/resources/bin/elasticsearch.in.bat

@@ -1,12 +1,15 @@
 @echo off
 
-if DEFINED JAVA_HOME goto cont
+IF DEFINED JAVA_HOME (
+  set JAVA=%JAVA_HOME%\bin\java.exe
+) ELSE (
+  FOR %%I IN (java.exe) DO set JAVA=%%~$PATH:I
+)
+IF NOT EXIST "%JAVA%" (
+  ECHO Could not find any executable java binary. Please install java in your PATH or set JAVA_HOME 1>&2
+  EXIT /B 1
+)
 
-:err
-ECHO JAVA_HOME environment variable must be set! 1>&2
-EXIT /B 1
-
-:cont
 set SCRIPT_DIR=%~dp0
 for %%I in ("%SCRIPT_DIR%..") do set ES_HOME=%%~dpfI
 

distribution/src/main/resources/bin/service.bat

@@ -28,27 +28,38 @@ if %bad_env_var% == 1 (
 )
 rem end TODO: remove for Elasticsearch 6.x
 
-if NOT DEFINED JAVA_HOME goto err
+IF DEFINED JAVA_HOME (
+  SET JAVA=%JAVA_HOME%\bin\java.exe
+) ELSE (
+  FOR %%I IN (java.exe) DO set JAVA=%%~$PATH:I
+)
+IF NOT EXIST "%JAVA%" (
+  ECHO Could not find any executable java binary. Please install java in your PATH or set JAVA_HOME 1>&2
+  EXIT /B 1
+)
+IF DEFINED JAVA_HOME GOTO :cont
 
+IF NOT "%JAVA:~-13%" == "\bin\java.exe" (
+  FOR /f "tokens=2 delims=[]" %%I IN ('dir %JAVA%') DO @set JAVA=%%I
+)
+IF "%JAVA:~-13%" == "\bin\java.exe" (
+  SET JAVA_HOME=%JAVA:~0,-13%
+)
+
+:cont
 if not "%CONF_FILE%" == "" goto conffileset
 
 set SCRIPT_DIR=%~dp0
 for %%I in ("%SCRIPT_DIR%..") do set ES_HOME=%%~dpfI
 
-rem Detect JVM version to figure out appropriate executable to use
-if not exist "%JAVA_HOME%\bin\java.exe" (
-echo JAVA_HOME points to an invalid Java installation (no java.exe found in "%JAVA_HOME%"^). Exiting...
-goto:eof
-)
-
-"%JAVA_HOME%\bin\java" -Xmx50M -version > nul 2>&1
+"%JAVA%" -Xmx50M -version > nul 2>&1
 
 if errorlevel 1 (
 	echo Warning: Could not start JVM to detect version, defaulting to x86:
 	goto x86
 )
 
-"%JAVA_HOME%\bin\java" -Xmx50M -version 2>&1 | "%windir%\System32\find" "64-Bit" >nul:
+"%JAVA%" -Xmx50M -version 2>&1 | "%windir%\System32\find" "64-Bit" >nul:
 
 if errorlevel 1 goto x86
 set EXECUTABLE=%ES_HOME%\bin\elasticsearch-service-x64.exe