Upgrade to java-21

docker/zookeeper-image/Dockerfile

@@ -1,4 +1,4 @@
-# backported from https://github.com/docker-library/openjdk/blob/master/18/jdk/slim-bullseye/Dockerfile
+# backported from https://github.com/docker-library/openjdk/blob/4c2b1a57869e24c5fcfbea6a17e558c710d4f6bd/21/jdk/slim-bullseye/Dockerfile
 FROM debian:bullseye-slim
 
 RUN set -eux; \
@@ -8,22 +8,24 @@ RUN set -eux; \
 	; \
 	rm -rf /var/lib/apt/lists/*
 
-ENV JAVA_HOME /usr/local/openjdk-17
+ENV JAVA_HOME /usr/local/openjdk-21
 ENV PATH $JAVA_HOME/bin:$PATH
 
 # Default to UTF-8 file.encoding
 ENV LANG C.UTF-8
+ENV JAVA_VERSION 21
+
 RUN set -eux; \
 	\
 	arch="$(dpkg --print-architecture)"; \
 	case "$arch" in \
 		'amd64') \
-			downloadUrl='https://download.oracle.com/java/17/latest/jdk-17_linux-x64_bin.tar.gz'; \
-			downloadSha256='https://download.oracle.com/java/17/latest/jdk-17_linux-x64_bin.tar.gz.sha256'; \
+			downloadUrl='https://download.oracle.com/java/21/latest/jdk-21_linux-x64_bin.tar.gz'; \
+			downloadSha256='https://download.oracle.com/java/21/latest/jdk-21_linux-x64_bin.tar.gz.sha256'; \
 			;; \
 		'arm64') \
-			downloadUrl='https://download.oracle.com/java/17/latest/jdk-17_linux-aarch64_bin.tar.gz'; \
-			downloadSha256='https://download.oracle.com/java/17/latest/jdk-17_linux-aarch64_bin.tar.gz.sha256'; \
+			downloadUrl='https://download.oracle.com/java/21/latest/jdk-21_linux-aarch64_bin.tar.gz'; \
+			downloadSha256='https://download.oracle.com/java/21/latest/jdk-21_linux-aarch64_bin.tar.gz.sha256'; \
 			;; \
 		*) echo >&2 "error: unsupported architecture: '$arch'"; exit 1 ;; \
 	esac; \