Docker compose connection between java and mysql container not possible

I have an java spring / hibernate application and I cant create a connection beween the mysql and java containers. When I start just the mysql Container and run the java application manualy in CMD it works fine. But once the java application runs in a container I get the following problem:

bookAPI | com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure
bookAPI |
bookAPI | The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
bookAPI |      at com.mysql.cj.jdbc.exceptions.SQLError.createCommunicationsException(SQLError.java:174) ~[mysql-connector-java-8.0.21.jar!/:8.0.21]
bookAPI |      at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:64) ~[mysql-connector-java-8.0.21.jar!/:8.0.21]

If I understand the error correctly the java container can send to the mysql container but not the other way around. I have linked the java container to the mysql container. Anyone knows how to connect these containers correctly?

My docker-compose.yml looks like this:

version: '3'
 
services:
  db:
    image: mysql:5.7
    container_name: mysql
    environment:
      MYSQL_ROOT_PASSWORD: aaaaaa
      MYSQL_DATABASE: bookAPI
      MYSQL_USER: aaaaaa
      MYSQL_PASSWORD: aaaaaa
    ports:
      - 3306:3306
  phpmyadmin:
    image: phpmyadmin/phpmyadmin
    container_name: phpmyadmin
    links:
      - db
    environment:
      PMA_HOST: db
      PMA_PORT: 3306
      PMA_ARBITRARY: 1
    restart: always
    ports:
      - 8081:80
  java:
    container_name: bookAPI
    image: openjdk:8
    depends_on:
    - db
    volumes:
    - ./:/app
    working_dir: /app
    command: bash -c "cd /app && java -jar bookAPI.jar"  
    stdin_open: true
    tty: true
    ports:
      - 8080:8080
    links:
      - db

You can also directly override the applications.properties with docker-compose environment variables like this :

  java:
    container_name: bookAPI
    image: openjdk:8
    volumes:
    - ./:/app
    working_dir: /app
    command: bash -c "cd /app && java -jar bookAPI.jar"
    stdin_open: true
    tty: true
    environment:
      spring.datasource.url="jdbc:mysql://db:3306/bookAPI""
    links:
      - db
    ports:
      - 8080:8080

I would recomment you tu use depends_on db instead of links

depends_on:
  - db


</details>



# 答案2
**得分**: 1

好的，我已经解决了这个问题。要将Spring应用程序与另一个Docker容器连接起来，您需要将application.properties文件中的url值从localhost或IP更改为Docker MySQL容器的名称。当在本地运行或运行maven install时，这可能会有些棘手，所以最佳做法是在容器中启动应用程序时进行覆盖。

```yaml
  java:
    container_name: bookAPI
    image: openjdk:8
    volumes:
    - ./:/app
    working_dir: /app
    command: bash -c "cd /app && java -jar bookAPI.jar --spring.datasource.url='jdbc:mysql://db:3306/bookAPI'"
    stdin_open: true
    tty: true
    links:
      - db
    ports:
      - 8080:8080

  java:
    container_name: bookAPI
    image: openjdk:8
    volumes:
    - ./:/app
    working_dir: /app
    command: bash -c "cd /app && java -jar bookAPI.jar  --spring.datasource.url="jdbc:mysql://db:3306/bookAPI""  
    stdin_open: true
    tty: true
    links:
      - db
    ports:
      - 8080:8080