Dockerfiles

虽然可以将 Spring Boot uber jar 转换为 Docker 镜像，只需在 Dockerfile 中添加几行代码即可，但使用分层功能将生成优化后的镜像。当你创建一个包含层索引文件的 jar 时，spring-boot-jarmode-tools jar 将作为依赖项添加到你的 jar 中。通过在 classpath 中包含此 jar，你可以在一种特殊模式下启动你的应用，该模式允许引导代码运行与你的应用完全不同的内容，例如，提取层的内容。

tools 模式不能用于包含启动脚本的完全可执行 Spring Boot 归档文件。在构建打算与 extract 工具模式命令一起使用的 jar 文件时，请禁用启动脚本配置。

你可以通过以下方式使用 tools jar 模式启动你的 jar

$ java -Djarmode=tools -jar my-app.jar

这将提供以下输出

Usage:
  java -Djarmode=tools -jar my-app.jar

Available commands:
  extract      Extract the contents from the jar
  list-layers  List layers from the jar that can be extracted
  help         Help about any command

extract 命令可以轻松地将应用拆分成层，以便添加到 Dockerfile 中。以下是使用 jarmode 的 Dockerfile 示例。

# Perform the extraction in a separate builder container
FROM bellsoft/liberica-openjre-debian:24-cds AS builder
WORKDIR /builder
# This points to the built jar file in the target folder
# Adjust this to 'build/libs/*.jar' if you're using Gradle
ARG JAR_FILE=target/*.jar
# Copy the jar file to the working directory and rename it to application.jar
COPY ${JAR_FILE} application.jar
# Extract the jar file using an efficient layout
RUN java -Djarmode=tools -jar application.jar extract --layers --destination extracted

# This is the runtime container
FROM bellsoft/liberica-openjre-debian:24-cds
WORKDIR /application
# Copy the extracted jar contents from the builder container into the working directory in the runtime container
# Every copy step creates a new docker layer
# This allows docker to only pull the changes it really needs
COPY --from=builder /builder/extracted/dependencies/ ./
COPY --from=builder /builder/extracted/spring-boot-loader/ ./
COPY --from=builder /builder/extracted/snapshot-dependencies/ ./
COPY --from=builder /builder/extracted/application/ ./
# Start the application jar - this is not the uber jar used by the builder
# This jar only contains application code and references to the extracted jar files
# This layout is efficient to start up and CDS/AOT cache friendly
ENTRYPOINT ["java", "-jar", "application.jar"]

假设上面的 Dockerfile 位于当前目录，你可以使用 docker build . 构建你的 Docker 镜像，或者选择性地指定应用 jar 的路径，如下例所示

$ docker build --build-arg JAR_FILE=path/to/myapp.jar .

这是一个多阶段的 Dockerfile。构建器阶段会提取后续所需的目录。每个 COPY 命令都与由 jarmode 提取的层相关联。

当然，也可以不使用 jarmode 来编写 Dockerfile。你可以使用 unzip 和 mv 的组合将内容移动到正确的层，但 jarmode 简化了这一过程。此外，由 jarmode 创建的布局开箱即支持 CDS 和 AOT 缓存。

CDS

如果你想额外启用 CDS，可以使用这个 Dockerfile

# Perform the extraction in a separate builder container
FROM bellsoft/liberica-openjre-debian:24-cds AS builder
WORKDIR /builder
# This points to the built jar file in the target folder
# Adjust this to 'build/libs/*.jar' if you're using Gradle
ARG JAR_FILE=target/*.jar
# Copy the jar file to the working directory and rename it to application.jar
COPY ${JAR_FILE} application.jar
# Extract the jar file using an efficient layout
RUN java -Djarmode=tools -jar application.jar extract --layers --destination extracted

# This is the runtime container
FROM bellsoft/liberica-openjre-debian:24-cds
WORKDIR /application
# Copy the extracted jar contents from the builder container into the working directory in the runtime container
# Every copy step creates a new docker layer
# This allows docker to only pull the changes it really needs
COPY --from=builder /builder/extracted/dependencies/ ./
COPY --from=builder /builder/extracted/spring-boot-loader/ ./
COPY --from=builder /builder/extracted/snapshot-dependencies/ ./
COPY --from=builder /builder/extracted/application/ ./
# Execute the CDS training run
RUN java -XX:ArchiveClassesAtExit=application.jsa -Dspring.context.exit=onRefresh -jar application.jar
# Start the application jar with CDS enabled - this is not the uber jar used by the builder
# This jar only contains application code and references to the extracted jar files
# This layout is efficient to start up and CDS friendly
ENTRYPOINT ["java", "-XX:SharedArchiveFile=application.jsa", "-jar", "application.jar"]

这与上面的 Dockerfile 大致相同。作为最后几步，它通过一次训练运行创建 CDS 归档文件，并将 CDS 参数传递给 java -jar。

AOT 缓存

如果你想额外启用 AOT 缓存，可以使用这个 Dockerfile

# Perform the extraction in a separate builder container
FROM bellsoft/liberica-openjre-debian:24-cds AS builder
WORKDIR /builder
# This points to the built jar file in the target folder
# Adjust this to 'build/libs/*.jar' if you're using Gradle
ARG JAR_FILE=target/*.jar
# Copy the jar file to the working directory and rename it to application.jar
COPY ${JAR_FILE} application.jar
# Extract the jar file using an efficient layout
RUN java -Djarmode=tools -jar application.jar extract --layers --destination extracted

# This is the runtime container
FROM bellsoft/liberica-openjre-debian:24-cds
WORKDIR /application
# Copy the extracted jar contents from the builder container into the working directory in the runtime container
# Every copy step creates a new docker layer
# This allows docker to only pull the changes it really needs
COPY --from=builder /builder/extracted/dependencies/ ./
COPY --from=builder /builder/extracted/spring-boot-loader/ ./
COPY --from=builder /builder/extracted/snapshot-dependencies/ ./
COPY --from=builder /builder/extracted/application/ ./
# Execute the AOT cache training run
RUN java -XX:AOTMode=record -XX:AOTConfiguration=app.aotconf -Dspring.context.exit=onRefresh -jar application.jar
RUN java -XX:AOTMode=create -XX:AOTConfiguration=app.aotconf -XX:AOTCache=app.aot -jar application.jar && rm app.aotconf
# Start the application jar with AOT cache enabled - this is not the uber jar used by the builder
# This jar only contains application code and references to the extracted jar files
# This layout is efficient to start up and AOT cache friendly
ENTRYPOINT ["java", "-XX:AOTCache=app.aot", "-jar", "application.jar"]

这与上面的 Dockerfile 大致相同。作为最后几步，它通过一次训练运行创建 AOT 缓存文件，并将 AOT 缓存参数传递给 java -jar。