future versions of Elasticsearch will require Java 11; your Java version from [/usr/local/jdk1.8.0_1/jre] does not meet this requirement

使用ES7版本时，启动或者执行ES命令，提示上面错误信息。这是由于ES7使用的高版本的jdk。如果不想升级服务的jdk，可以通过修改elasticsearch-env配置文件，使用ES内置的jdk来解决上面的问题。

# now set the path to java
# 注释掉原来的配置信息
#if [ ! -z "$JAVA_HOME" ]; then
#  JAVA="$JAVA_HOME/bin/java"
#  JAVA_TYPE="JAVA_HOME"
#else
#  if [ "$(uname -s)" = "Darwin" ]; then
#    # macOS has a different structure
#    JAVA="$ES_HOME/jdk.app/Contents/Home/bin/java"
#  else
#    JAVA="$ES_HOME/jdk/bin/java"
#  fi
#  JAVA_TYPE="bundled jdk"
#fi
# 如何为新的配置信息
if [ ! -z "$JAVA_HOME" ]; then
  JAVA="$ES_HOME/jdk/bin/java"
  JAVA_TYPE="JAVA_HOME"
else
  if [ "$(uname -s)" = "Darwin" ]; then
    # macOS has a different structure
    JAVA="$ES_HOME/jdk.app/Contents/Home/bin/java"
  else
    JAVA="$ES_HOME/jdk/bin/java"
  fi  
  JAVA_TYPE="bundled jdk"
fi