add support of JAVA_HOME environment

fix find in root directory(/) when use in systemd

src/packaging/bin/cassandra-reaper

@@ -14,7 +14,7 @@
 #  See the License for the specific language governing permissions and
 #  limitations under the License.
 
-REAPER_JAR=$(find . -maxdepth 4 -regex '.*/cassandra-reaper-.*[0-9rT]\.jar')
+REAPER_JAR=$(find /usr/share/cassandra-reaper/ -maxdepth 4 -regex '.*/cassandra-reaper-.*[0-9rT]\.jar')
 
 if [ $REAPER_JAR ]; then
     echo "Using reaper in target"
@@ -36,6 +36,28 @@ else
     CONFIG_PATH="$@"
 fi
 
+# Use JAVA_HOME if set, otherwise look for java in PATH
+if [ -n "$JAVA_HOME" ]; then
+    # Why we can't have nice things: Solaris combines x86 and x86_64
+    # installations in the same tree, using an unconventional path for the
+    # 64bit JVM.  Since we prefer 64bit, search the alternate path first,
+    # (see https://issues.apache.org/jira/browse/CASSANDRA-4638).
+    for java in "$JAVA_HOME"/bin/amd64/java "$JAVA_HOME"/bin/java; do
+        if [ -x "$java" ]; then
+            JAVA="$java"
+            break
+        fi
+    done
+else
+    JAVA=java
+fi
+
+if [ -z $JAVA ] ; then
+    echo Unable to find java executable. Check JAVA_HOME and PATH environment variables. >&2
+    exit 1;
+fi
+
+
 JVM_OPTS=(
     # it is safe and performant to disable assertions in production environments (ie replace `-ea` with `-da`)
     -ea
@@ -47,7 +69,7 @@ JVM_OPTS=(
     -Djava.net.preferIPv4Stack=true
     )
 
-exec java ${JVM_OPTS[@]} \
+exec ${JAVA} ${JVM_OPTS[@]} \
     -cp ${CLASS_PATH} \
     io.cassandrareaper.ReaperApplication \
     server ${CONFIG_PATH}