select-java: query java version using -XshowSettings

instead of parsing the output of `-version`, parse output of
`-XshowSettings:properties`, whose format is more predicable.
as on EL9, we have

> Picked up JAVA_TOOL_OPTIONS: openjdk version "11.0.19" 2023-04-18 LTS OpenJDK Runtime Environment (Red_Hat-11.0.19.0.7-1.el9_1) (build 11.0.19+7-LTS) OpenJDK 64-Bit Server VM (Red_Hat-11.0.19.0.7-1.el9_1) (build 11.0.19+7-LTS, mixed mode, sharing)

while on fedora 38, jre-1.8 prints

> openjdk version "1.8.0_362"

jre-11 prints

> openjdk version "11.0.19" 2023-04-18

before this change, we just use `"` as the field separator for awk,
this works, but the parsing algorithm is fragile. so let's use the
"java.specification.version" property instead, it is always printed
like

>     java.specification.version = 1.8

so, after this change, we split this line with " = ", and pick the
last field, i.e., the value of `java.specification.version`.
also, in this change, we are using the case clause for better readability.

also, in this change, instead of dispatch the logic by the distro
id, we just check all JVMs located under /usr/lib/jvm, and pick the
first match. this simplifies the existing complicated implementation.

also, instead of silently returning status code of 1, print error messages
for better user experience.

Fixes scylladb#212
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>

scripts/select-java

@@ -1,52 +1,29 @@
 #!/bin/bash
 
-function select_java_debian() {
-    local java
-    local arch
-    arch=$(dpkg --print-architecture)
+function select_java() {
+    local expected_java_versions
+    expected_java_versions=$@
 
-    for version in "11" "8"; do
-        java=/usr/lib/jvm/java-${version}-openjdk-${arch}/bin/java
-        if [ -e $java ]; then
-            echo $java
-            return
-        fi
+    for expected_java_version in $expected_java_versions; do
+        for java_home in /usr/lib/jvm/*; do
+            java=$java_home/bin/java
+            javaver=$($java -XshowSettings:properties -version 2>&1 | awk -F' = ' '/java.specification.version/ {print $NF}')
+            echo $javever
+            if [ "$javaver" = $expected_java_version ]; then
+                echo $java
+                return
+            fi
+        done
     done
 }
 
-function select_java_fedora() {
-    local java
-    for version in "11" "1.8.0"; do
-        java=/usr/lib/jvm/jre-${version}-openjdk/bin/java
-        if [ -e $java ]; then
-            echo $java
-            return
-        fi
-    done
-}
+# So far, scylla-jmx only works with Java 11 and Java 8, we prefer the newer
+# one for better upstream support.
+expected_java_versions="11 1.8"
 
-function select_java_others() {
-    javaver=$(/usr/bin/java -version 2>&1|head -n1|cut -f 3 -d " ")
-    if [[ "$javaver" =~ ^\"1.8.0 || "$javaver" =~ ^\"11.0. ]]; then
-        echo /usr/bin/java
-    fi
-}
-
-. /etc/os-release
-case "$ID" in
-    ubuntu|debian)
-        java=$(select_java_debian)
-        ;;
-    fedora|centos)
-        java=$(select_java_fedora)
-        ;;
-esac
-if [ -n "$java" ]; then
-    : # good
-elif [ -x /usr/bin/java ]; then
-    java=$(select_java_others)
-fi
+java=$(select_java $expected_java_versions)
 if [ -z "$java" ]; then
+    echo "Unable to find java executable" >& 2
     exit 1
 fi