install.sh: introduce Java existance check

[syuu1228]

Since we dropped Java check from unified installer and jmx, we need to do it on scylla-tools.

Related scylladb/scylladb#17969

[syuu1228]

This is part of scylladb/scylladb#17969, need to merge first.

[tchaikov]

might want to s/scylla-jmx/scylla-tools/ . probably we could be more specific though, like "tools like nodetool and cassandra-stress". but "scylla-tools" is the name used by https://github.com/scylladb/scylla-tools-java?tab=readme-ov-file#scylla-tools .

[tchaikov]

also, in scylla-jmx, select-java actually serves for use cases

• if we are not installing the package, it selects the java executable at runtime, see https://github.com/scylladb/scylla-jmx/blob/3328a229610daac8198a4133b496a9d7cb1de469/scripts/scylla-jmx#L134 .
• if we are installing the package using install.sh, install.sh is responsible for detecting the runtime environment for the java applications. so it also checks for the available java runtimes.

in this change, we only address the second use case, where we are installing scylla-tools using install.sh, but what about the first use case? please note, the existing check is performed by

scylla-tools-java/dist/common/cassandra.in.sh

Line 65 in 01ba3c1

java_ver_output=`"${JAVA:-java}" -version 2>&1`

, which just check if the java fulfills the needs, it does not pick a java runtime. so if user actually has openjdk-11 installed, but he/she doe not point /usr/bin/java to it, or export $JAVA so that it points to one of the supported java runtime, cassandra.in.sh fails.

[syuu1228]

also, in scylla-jmx, select-java actually serves for use cases

• if we are not installing the package, it selects the java executable at runtime, see https://github.com/scylladb/scylla-jmx/blob/3328a229610daac8198a4133b496a9d7cb1de469/scripts/scylla-jmx#L134 .
• if we are installing the package using install.sh, install.sh is responsible for detecting the runtime environment for the java applications. so it also checks for the available java runtimes.

in this change, we only address the second use case, where we are installing scylla-tools using install.sh, but what about the first use case? please note, the existing check is performed by

scylla-tools-java/dist/common/cassandra.in.sh

Line 65 in 01ba3c1

java_ver_output=`"${JAVA:-java}" -version 2>&1`

, which just check if the java fulfills the needs, it does not pick a java runtime. so if user actually has openjdk-11 installed, but he/she doe not point /usr/bin/java to it, or export $JAVA so that it points to one of the supported java runtime, cassandra.in.sh fails.

We need some code to detect Java on scylla-tools's install.sh, since we are dropping it from unified installer.
But, as you descripbed, Java detection method between select-java and cassandra.in.sh are different, I think we should not use select-java here.
So I pushed new code to detect Java just like cassandra.in.sh, and dropped select-java.

[tchaikov]

what if user installs, for instance, openjdk-21 and have it in $PATH? and we are not checking for openjdk-11, but a random java executable in the $PATH. so even if this test passes, it does not imply that we have openjdk-11 around.