A bash script to attempt to locate the computer's default JVM and update it's time zone database file

update_jvm_tzdb.sh

#!/bin/bash

# use of this script means you agree to hold harmless and indemnify the author of the script
# use at your own risk

# usage example: update_jmv_tzdb.sh 2024a

if [ $# -eq 0 ]; then
  echo "TZDB version argument missing"
  exit
fi
if [ -z "$1" ]; then
  echo "TZDB version argument empty"
  exit
fi

# locate the tzdb.dat file
JAVA_EXE_PATH="`readlink -f /usr/bin/java`"
JAVA_JRE_BIN_DIR_PATH="`dirname ${JAVA_EXE_PATH}`"
JAVA_JRE_LIB_DIR_PATH="`dirname ${JAVA_JRE_BIN_DIR_PATH}`/lib"
JAVA_TZDB_PATH="${JAVA_JRE_LIB_DIR_PATH}/tzdb.dat"

# if tzdb.dat is not found exit
if [ ! -f "$JAVA_TZDB_PATH" ]; then
  echo "Unable to locate existing TZDB ${JAVA_TZDB_PATH}"
  exit
fi

# get the version of the existing tzdb.dat
TZDB_OLD_VERSION=`head -c 16 ${JAVA_TZDB_PATH} | tail -c 5`

echo "Located existing TZDB ${TZDB_OLD_VERSION} ${JAVA_TZDB_PATH}"

# download new tzdb.dat file based on arguments
TZDB_NEW_VERSION="${1}"
TZDB_DOWNLOAD_URL="https://raw.githubusercontent.com/jeremywall/java-tzdb-builder/main/releases/${TZDB_NEW_VERSION}/tzdb${TZDB_NEW_VERSION}.dat"

HTTP_RESPONSE_CODE=`curl -O -f -w "%{http_code}" "${TZDB_DOWNLOAD_URL}"`

echo "Download TZDB ${TZDB_NEW_VERSION} HTTP Response ${HTTP_RESPONSE_CODE}"

# if not HTTP 200 then exit
if [ "200" != "${HTTP_RESPONSE_CODE}" ]; then
  echo "Failed to download TZDB ${TZDB_NEW_VERSION} from ${TZDB_DOWNLOAD_URL}"
  exit
fi

# backup existing tzdb.dat
cp "${JAVA_TZDB_PATH}" "${JAVA_TZDB_PATH}.${TZDB_OLD_VERSION}.bak"
echo "Backed up existing TZDB to ${JAVA_TZDB_PATH}.${TZDB_OLD_VERSION}.bak"

# copy new tzdb.dat into place
cp "tzdb${TZDB_NEW_VERSION}.dat" "${JAVA_TZDB_PATH}"
echo "Copied new TZDB to ${JAVA_TZDB_PATH}"

# set permissions on tzdb.dat
chmod 644 "${JAVA_TZDB_PATH}"
echo "Setting TZDB file permissions to 644"

echo "Now you need to restart all Java applications on this server"