docker-compose build 每次下载几个 pom 依赖

Question

我正在使用 Heroku Java Docker Image 和 docker-compose 在本地运行基于 dropwizard java 的 Web 服务。

当我运行docker-compose build web 命令构建代码时，它每次都会下载一些依赖项。因此构建过程的周转时间增加了。

我的项目 docker 文件只有一行：FROM heroku/java

这里是构建日志：

[INFO] ------------------------------------------------------------------------
[INFO] Building generator-app-server 0.0.2-SNAPSHOT
[INFO] ------------------------------------------------------------------------
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-clean-plugin/2.5/maven-clean-plugin-2.5.pom
Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-clean-plugin/2.5/maven-clean-plugin-2.5.pom (4 KB at 0.7 KB/sec)
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-plugins/22/maven-plugins-22.pom
Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-plugins/22/maven-plugins-22.pom (13 KB at 9.0 KB/sec)
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-clean-plugin/2.5/maven-clean-plugin-2.5.jar
Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-clean-plugin/2.5/maven-clean-plugin-2.5.jar (25 KB at 14.7 KB/sec)
[INFO] 
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ generator-app-server ---
Downloading: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-utils/3.0/plexus-utils-3.0.pom
Downloaded: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-utils/3.0/plexus-utils-3.0.pom (4 KB at 5.4 KB/sec)
Downloading: https://repo.maven.apache.org/maven2/org/sonatype/spice/spice-parent/16/spice-parent-16.pom
Downloaded: https://repo.maven.apache.org/maven2/org/sonatype/spice/spice-parent/16/spice-parent-16.pom (9 KB at 4.9 KB/sec)
Downloading: https://repo.maven.apache.org/maven2/org/sonatype/forge/forge-parent/5/forge-parent-5.pom
Downloaded: https://repo.maven.apache.org/maven2/org/sonatype/forge/forge-parent/5/forge-parent-5.pom (9 KB at 5.0 KB/sec)
Downloading: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-utils/3.0/plexus-utils-3.0.jar
Downloaded: https://repo.maven.apache.org/maven2/org/codehaus/plexus/plexus-utils/3.0/plexus-utils-3.0.jar (221 KB at 20.0 KB/sec)
[INFO] Deleting /app/user/target
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ generator-app-server ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 7 resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.6.1:compile (default-compile) @ generator-app-server ---
Downloading: https://repo.maven.apache.org/maven2/org/mapstruct/mapstruct-processor/1.1.0.Final/mapstruct-processor-1.1.0.Final.jar
Downloaded: https://repo.maven.apache.org/maven2/org/mapstruct/mapstruct-processor/1.1.0.Final/mapstruct-processor-1.1.0.Final.jar (1502 KB at 24.5 KB/sec)
Downloading: https://repo.maven.apache.org/maven2/org/mapstruct/mapstruct-processor/1.1.0.Final/mapstruct-processor-1.1.0.Final.pom
Downloaded: https://repo.maven.apache.org/maven2/org/mapstruct/mapstruct-processor/1.1.0.Final/mapstruct-processor-1.1.0.Final.pom (12 KB at 4.9 KB/sec)

docker-compose build 没有为上述库使用缓存的依赖项。如何强制使用缓存的依赖？

谷歌了很多，但没有运气。如果有人遇到并修复过，请分享。

更新：

Dockerfile
FROM heroku/java

docker-compose.yml
web:
  build: .
  command: 'bash -c ''java $JAVA_OPTS -jar target/generator-app-server-0.0.2-SNAPSHOT.jar db migrate config.yml && java $JAVA_OPTS -Ddw.server.connector.port=$PORT -jar target/generator-app-server-0.0.2-SNAPSHOT.jar server config.yml'''
  working_dir: /app/user
  environment:
    PORT: 8080
    DATABASE_URL: 'postgres://postgres:@herokuPostgresql:5432/postgres'
  ports:
    - '8080:8080'
  links:
    - herokuPostgresql
shell:
  build: .
  command: bash
  working_dir: /app/user
  environment:
    PORT: 8080
    DATABASE_URL: 'postgres://postgres:@herokuPostgresql:5432/postgres'
  ports:
    - '8080:8080'
  links:
    - herokuPostgresql
  volumes:
    - '.:/app/user'
herokuPostgresql:
  image: postgres

Answer 1

我之前的回答没有意义（我错误地认为 Maven 依赖项是在运行时处理的，而是在 ONBUILD 指令处处理）。但我会尝试再次解释为什么这些特定的依赖项没有被缓存。

问题中列出的下载依赖项来自 Maven clean 的内置插件。在父 Dockerfile 中，我们在 https://github.com/heroku/docker-java/blob/master/Dockerfile#L14 下载项目依赖项（POM 中的所有内容）。然后，稍后在Dockerfile 中，它在https://github.com/heroku/docker-java/blob/master/Dockerfile#L18 运行clean。由于maven-clean-plugin 不是您的 POM 的一部分，它会在清理步骤中自动下载（它不会从之前的 Dockerfile 指令中缓存）。

因此，如果您还想缓存 maven-clean-plugin，您可能需要将其作为依赖项添加到您的 POM 中（您可能只需 <scope>import</scope> 就可以逃脱）。