在Dockerfile中，如果直接在CMD命令中写类似于java -Xmx2g -Xms2g -Xmn1g -jar xxxxxx.jar这样的命令，容器启动时会报错：
Invalid maximum heap size: -Xmx2g -Xms2g -Xmn1g -jar xxxxxx.jar
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.
解决方案
ENV JAVA_OPT="-Xmx2g -Xms2g -Xmn1g"
CMD java $JAVA_OPT -jar xxxxxx.jar