基于layer jars构建docker镜像

经过一番折腾之后，还是觉得老老实实的写Dockerfile更香，Spring Boot 2.3.1对layer jars的支持与2.3.0有所变化，网上的资料大部分都是过时了的，正确步骤如下：

1. pom里开启layer jars支持

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

2. 编写Dockerfile，下面是一个简单的例子

   FROM adoptopenjdk:8-jre-hotspot as builder
   WORKDIR application
   ARG JAR_FILE=target/*.jar
   COPY ${JAR_FILE} application.jar
   RUN java -Djarmode=layertools -jar application.jar extract
   FROM adoptopenjdk:8-jre-hotspot
   WORKDIR application
   COPY --from=builder application/dependencies/ ./
   COPY --from=builder application/spring-boot-loader/ ./
   COPY --from=builder application/snapshot-dependencies/ ./
   COPY --from=builder application/application/ ./
   ENTRYPOINT ["java", "org.springframework.boot.loader.JarLauncher"]

3. 最后编译即可。

   docker build . -t tomu:v0.0.1