等待docker容器在circleci中准备就绪

我是这样定义的

start_selenium: &start_selenium
    name: Download & Run Selenium Stand alone Server
    command: |
      curl -O https://selenium-release.storage.googleapis.com/3.141/selenium-server-standalone-3.141.59.jar
      java -jar selenium-server-standalone-3.141.59.jar -log selenium.log
      java --version
    background: true

jobs: 
  docker:

  - image: circleci/php:7.2.30      
  - image: circleci/openjdk
  - image: circleci/mariadb:10.3
  steps:
      - run: *start_selenium

还有像这样的工作

start_selenium: &start_selenium
    name: Download & Run Selenium Stand alone Server
    command: |
      curl -O https://selenium-release.storage.googleapis.com/3.141/selenium-server-standalone-3.141.59.jar
      java -jar selenium-server-standalone-3.141.59.jar -log selenium.log
      java --version
    background: true

jobs: 
  docker:

  - image: circleci/php:7.2.30      
  - image: circleci/openjdk
  - image: circleci/mariadb:10.3
  steps:
      - run: *start_selenium

但问题是，start_selenium在docker映像准备就绪之前运行，它表示未定义“java”命令。