支持 Docker / Buildpack 镜像构建

云原生buildpacks(CNB)，一种再也不需要dockerfile并将源代码转换为Docker Image的标准。

SpringBoot 2.3 开启方式

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <configuration>
      <layers>
        <enabled>true</enabled>
      </layers>
    </configuration>
  </plugin>

bootJar {
	layered()
}

概述

1. 分层jar 的思想：根据规则把jar 细分。
2. SpringBoot 继承这个思想发布**「layertools」** 工具，该功能集成进了**「org.springframework.boot」**插件

分析过程

1. 新建一个最简单的SpringBoot2.4 项目

2. bootJar 后解压

   ├── BOOT-INF
   │   ├── classes
   │   ├── classpath.idx
   │   ├── layers.idx
   │   └── lib
   ├── META-INF
   │   └── MANIFEST.MF
   └── org
       └── springframework
   
   layers.idx 内容
   - "dependencies":
     - "BOOT-INF/lib/"
   - "spring-boot-loader":
     - "org/"
   - "snapshot-dependencies":
   - "application":
     - "BOOT-INF/classes/"
     - "BOOT-INF/classpath.idx"
     - "BOOT-INF/layers.idx"
     - "META-INF/"
   
   MANIFEST.MF 内容
   Manifest-Version: 1.0
   Main-Class: org.springframework.boot.loader.JarLauncher
   Start-Class: com.vector.layerjar.LayerjarApplication
   Spring-Boot-Version: 2.4.0
   Spring-Boot-Classes: BOOT-INF/classes/
   Spring-Boot-Lib: BOOT-INF/lib/
   Spring-Boot-Classpath-Index: BOOT-INF/classpath.idx
   Spring-Boot-Layers-Index: BOOT-INF/layers.idx
   

   可见，划分为4 层

   • dependencies 依赖层，项目所以依赖的第三方库，release 版本的
   • spring-boot-loader 加载层，用于jar加载程序类，SpringBoot 的高级加载
   • snapshot-dependencies 快照依赖层，可能经常升级的依赖
   • application 应用层，自己写的代码和资源

3. 打包成docker 镜像

   # 基础镜像, 需要的环境就是JDK
   FROM jboss/base-jdk:11 as builder
   
   # 使用root 操作
   USER root
   
   # 工作目录
   WORKDIR /usr/local/owl
   
   ARG JAR_FILE=./build/libs/layerjar-1.0.0.jar
   
   COPY ${JAR_FILE} app.jar
   
   RUN java -Djarmode=layertools -jar app.jar extract
   
   FROM jboss/base-jdk:11
   
   # 使用root 操作
   USER root
   
   # 工作目录
   WORKDIR /usr/local/owl
   
   # 分层复制class,jar 文件
   COPY --from=builder /usr/local/owl/dependencies/ ./
   COPY --from=builder /usr/local/owl/spring-boot-loader/ ./
   COPY --from=builder /usr/local/owl/snapshot-dependencies/ ./
   COPY --from=builder /usr/local/owl/application/ ./
   
   ENV PARAMS=""
   
   # 运行jar 文件
   ENTRYPOINT [ "sh", "-c", "java $PARAMS -Dfile.encoding=UTF-8 org.springframework.boot.loader.JarLauncher" ]
   

   # 编译
   docker build . --tag layerjar
   
   # 运行
   → docker run -p 80:80 -e PARAMS="-Dserver.port=80" -it layerjar 
   
     .   ____          _            __ _ _
    /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
   ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
    \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
     '  |____| .__|_| |_|_| |_\__, | / / / /
    =========|_|==============|___/=/_/_/_/
    :: Spring Boot ::                (v2.4.0)
   
   2020-11-16 10:34:03.267  INFO 1 --- [           main] com.vector.layerjar.LayerjarApplication  : Starting LayerjarApplication using Java 11.0.1 on a35a3c9d0ef1 with PID 1 (/usr/local/owl/BOOT-INF/classes started by root in /usr/local/owl)
   2020-11-16 10:34:03.274  INFO 1 --- [           main] com.vector.layerjar.LayerjarApplication  : No active profile set, falling back to default profiles: default
   2020-11-16 10:34:05.761  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 80 (http)
   2020-11-16 10:34:05.782  INFO 1 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
   2020-11-16 10:34:05.783  INFO 1 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.39]
   2020-11-16 10:34:05.925  INFO 1 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
   2020-11-16 10:34:05.929  INFO 1 --- [           main] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 2452 ms
   2020-11-16 10:34:06.400  INFO 1 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
   2020-11-16 10:34:06.924  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 80 (http) with context path ''
   2020-11-16 10:34:06.954  INFO 1 --- [           main] com.vector.layerjar.LayerjarApplication  : Started LayerjarApplication in 4.838 seconds (JVM running for 5.741)
   2020-11-16 10:34:10.655  INFO 1 --- [p-nio-80-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
   2020-11-16 10:34:10.656  INFO 1 --- [p-nio-80-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
   2020-11-16 10:34:10.659  INFO 1 --- [p-nio-80-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 2 ms
   

自定义分层

实际的项目中，常常拆分成多个项目，打包成jar相互依赖，这些jar 也是经常改变的。

那么这些jar 包就应该移到snapshot-dependencies，application 或在application 中间再加一层

# 基础镜像, 需要的环境就是JDK
FROM jboss/base-jdk:11 as builder
...
# 特殊处理自定义的依赖
RUN mkdir -p ./snapshot-dependencies/BOOT-INF/lib
RUN mv ./dependencies/BOOT-INF/lib/OwlCommons-*.jar ./snapshot-dependencies/BOOT-INF/lib/

FROM jboss/base-jdk:11
...