feat(mcserver): add javabin variable to choose the Java binary (#5214)

Add javabin (default "java") to mcserver, pmcserver, wmcserver and vpmcserver and use it in preexecutable. The default keeps the current PATH lookup, so existing servers behave the same. Setting a full path lets each server use its own JDK when several are installed.

Fixes #3493

lgsm/config-default/config-lgsm/mcserver/_default.cfg

@@ -10,6 +10,7 @@
 
 ## Predefined Parameters | https://docs.linuxgsm.com/configuration/start-parameters
 javaram="1024" # -Xmx$1024M
+javabin="java"
 
 ## Server Parameters | https://docs.linuxgsm.com/configuration/start-parameters#additional-parameters
 startparameters="nogui"
@@ -183,7 +184,7 @@ glibc="null"
 ## Game Server Directories
 systemdir="${serverfiles}"
 executabledir="${serverfiles}"
-preexecutable="java -Xmx${javaram}M -jar"
+preexecutable="${javabin} -Xmx${javaram}M -jar"
 executable="./minecraft_server.jar"
 servercfgdir="${systemdir}"
 servercfg="server.properties"

lgsm/config-default/config-lgsm/pmcserver/_default.cfg

@@ -10,6 +10,7 @@
 
 ## Predefined Parameters | https://docs.linuxgsm.com/configuration/start-parameters
 javaram="1024" # -Xmx$1024M
+javabin="java"
 
 ## Server Parameters | https://docs.linuxgsm.com/configuration/start-parameters#additional-parameters
 startparameters="nogui"
@@ -181,7 +182,7 @@ glibc="null"
 ## Game Server Directories
 systemdir="${serverfiles}"
 executabledir="${serverfiles}"
-preexecutable="java -Xmx${javaram}M -jar"
+preexecutable="${javabin} -Xmx${javaram}M -jar"
 executable="./paper.jar"
 servercfgdir="${systemdir}"
 servercfg="server.properties"

lgsm/config-default/config-lgsm/vpmcserver/_default.cfg

@@ -10,6 +10,7 @@
 
 ## Predefined Parameters | https://docs.linuxgsm.com/configuration/start-parameters
 javaram="1024" # -Xmx$1024M
+javabin="java"
 
 ## Server Parameters | https://docs.linuxgsm.com/configuration/start-parameters#additional-parameters
 startparameters=""
@@ -182,7 +183,7 @@ glibc="null"
 ## Game Server Directories
 systemdir="${serverfiles}"
 executabledir="${serverfiles}"
-preexecutable="java -Xmx${javaram}M -XX:+UseG1GC -XX:G1HeapRegionSize=4M -XX:+UnlockExperimentalVMOptions -XX:+ParallelRefProcEnabled -XX:+AlwaysPreTouch -XX:MaxInlineLevel=15 -jar"
+preexecutable="${javabin} -Xmx${javaram}M -XX:+UseG1GC -XX:G1HeapRegionSize=4M -XX:+UnlockExperimentalVMOptions -XX:+ParallelRefProcEnabled -XX:+AlwaysPreTouch -XX:MaxInlineLevel=15 -jar"
 executable="./velocity.jar"
 servercfgdir="${systemdir}"
 servercfg="velocity.toml"

lgsm/config-default/config-lgsm/wmcserver/_default.cfg

@@ -10,6 +10,7 @@
 
 ## Predefined Parameters | https://docs.linuxgsm.com/configuration/start-parameters
 javaram="1024" # -Xmx$1024M
+javabin="java"
 
 ## Server Parameters | https://docs.linuxgsm.com/configuration/start-parameters#additional-parameters
 startparameters="nogui"
@@ -181,7 +182,7 @@ glibc="null"
 ## Game Server Directories
 systemdir="${serverfiles}"
 executabledir="${serverfiles}"
-preexecutable="java -Xmx${javaram}M -jar"
+preexecutable="${javabin} -Xmx${javaram}M -jar"
 executable="./waterfall.jar"
 servercfgdir="${systemdir}"
 servercfg="config.yml"