Dockerfiles

虽然可以使用 Dockerfile 中的几行代码将 Spring Boot 胖 JAR 包转换为 Docker 镜像，但使用分层特性将会生成一个优化的镜像。当您创建一个包含分层索引文件的 JAR 包时，spring-boot-jarmode-tools JAR 将作为依赖项添加到您的 JAR 包中。通过将此 JAR 包添加到类路径中，您可以在特殊模式下启动您的应用程序，该模式允许引导代码运行与您的应用程序完全不同的内容，例如，提取分层的内容。

以下是您如何通过 tools jar 模式启动您的 JAR 包

$ 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 命令可用于轻松地将应用程序拆分为多个层，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:25-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:25-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 AOT cache (and CDS) friendly
ENTRYPOINT ["java", "-jar", "application.jar"]

假设上述 Dockerfile 位于当前目录中，您的 Docker 镜像可以通过 docker build . 构建，或者选择性地指定您的应用程序 JAR 包的路径，如以下示例所示

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

这是一个多阶段 Dockerfile。构建器阶段提取以后需要的目录。每个 COPY 命令都与 jarmode 提取的层相关。

当然，Dockerfile 也可以不使用 jarmode 来编写。您可以使用 unzip 和 mv 的组合将文件移动到正确的层，但 jarmode 简化了这一点。此外，jarmode 创建的布局开箱即用，兼容 AOT 缓存（和 CDS）。

AOT 缓存

如果您使用的是 Java < 24，则 AOT 缓存不可用。您必须改用 CDS。

如果您想额外启用 AOT 缓存，您可以使用此 Dockerfile

# Perform the extraction in a separate builder container
FROM bellsoft/liberica-openjre-debian:25-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:25-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:AOTCacheOutput=app.aot -Dspring.context.exit=onRefresh -jar application.jar
# 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。作为最后一步，它通过执行训练运行来创建 AOT 缓存文件，并将 AOT 缓存参数传递给 java -jar。

CDS

如果您使用的是 Java 24 或更高版本，请使用 AOT 缓存而不是 CDS。

如果您想额外启用 CDS，您可以使用此 Dockerfile

# Perform the extraction in a separate builder container
FROM bellsoft/liberica-openjre-debian:25-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:25-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。作为最后一步，它通过执行训练运行来创建 CDS 归档，并将 CDS 参数传递给 java -jar。