构建SpringBoot应用Docker镜像

准备工作

使用到的工具及运行环境：

JDK 1.8 及以上
Gradle 4+ 或 Maven 3.2+
开发工具
- Spring Tool Suite (STS)
- IntelliJ IDEA

创建SpringBoot应用

这边我是使用 IntelliJ IDEA 创建的，你也可以通过这种方式创建然后导入到IDE中 http://start.spring.io/

在 pom.xml 中添加 docker maven插件：

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.1.9.RELEASE</version><relativePath/> <!-- lookup parent from repository --></parent><groupId>com.xumiao</groupId><artifactId>spring-boot-docker</artifactId><version>0.0.1-SNAPSHOT</version><name>spring-boot-docker</name><description>Demo project for Spring Boot</description><properties><java.version>1.8</java.version><docker.image.prefix>springio</docker.image.prefix></properties><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin><!--build docker image--><plugin><groupId>com.spotify</groupId><artifactId>dockerfile-maven-plugin</artifactId><version>1.4.9</version><configuration><repository>${docker.image.prefix}/${project.artifactId}</repository></configuration></plugin><!-- tag::unpack[] --><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-dependency-plugin</artifactId><executions><execution><id>unpack</id><phase>package</phase><goals><goal>unpack</goal></goals><configuration><artifactItems><artifactItem><groupId>${project.groupId}</groupId><artifactId>${project.artifactId}</artifactId><version>${project.version}</version></artifactItem></artifactItems></configuration></execution></executions></plugin><!-- end::unpack[] --></plugins></build></project>

在 SpringBootApplication 启动文件中添加个简单的路由：

@SpringBootApplication
@RestController
public class Application {@RequestMapping("/")public String home() {return "Hello Docker World";}public static void main(String[] args) {SpringApplication.run(Application.class, args);}}

编写Dockerfile

在项目根目录创建 Dockerfile 文件，内容如下，启动类名全路径根据实际情况填写

FROM openjdk:8-jdk-alpine
VOLUME /tmp
ARG DEPENDENCY=target/dependency
COPY ${DEPENDENCY}/BOOT-INF/lib /app/lib
COPY ${DEPENDENCY}/META-INF /app/META-INF
COPY ${DEPENDENCY}/BOOT-INF/classes /app
ENTRYPOINT ["java","-cp","app:app/lib/*","com.xumiao.springboot.docker.Application"]

FROM：基于openjdk镜像进行构建；第一条指令必须为FROM 指令。并且，如果在同一个Dockerfile中创建多个镜像时，可以使用多个FROM 指令（每个镜像一次）。

VOLUME：指向了一个 /tmp 的目录，由于 SpringBoot 使用内置的Tomcat容器，Tomcat 默认使用 /tmp 作为工作目录。效果就是在主机的 /var/lib/docker 目录下创建了一个临时文件，并连接到容器的/tmp；如果应用中有对文件系统进行写操作这个是必须要写的。

ARG：设置构建参数

COPY：复制本地主机的（为 Dockerfile 所在目录的相对路径）到容器中的 app 目录下

ENTRYPOINT：配置容器启动后执行的命令，并且不可被 docker run 提供的参数覆盖。每个 Dockerfile 中只能有一个 ENTRYPOINT ，当指定多个时，只有最后一个起效。

上面命令参考以下资料

https://jiajially.gitbooks.io/dockerguide/content/chapter_fastlearn/dockerfile_details.html
https://yeasy.gitbooks.io/docker_practice/image/dockerfile/

构建 Docker 镜像

启动 Docker 后在应用下目录执行以下 maven 命令开始构建

 mvn install dockerfile:build

执行完成后我们查看下构建好的 docker 镜像（docker image ps），如下：

springio/spring-boot-docker   latest              436d7666f2f3        About a minute ago   122MB
openjdk                       8-jdk-alpine        a3562aa0b991        5 months ago         105MB

运行 Docker 镜像

通过以下命令创建 docker 容器并运行：

docker run -p 8080:8080 -t springio/spring-boot-docker.   ____          _            __ _ _/\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \\\/  ___)| |_)| | | | | || (_| |  ) ) ) )'  |____| .__|_| |_|_| |_\__, | / / / /=========|_|==============|___/=/_/_/_/:: Spring Boot ::        (v2.1.9.RELEASE)2019-10-24 13:33:09.064  INFO 1 --- [           main] c.xumiao.springboot.docker.Application   : Starting Application on 9a8a14b6d1ec with PID 1 (/app started by root in /)
2019-10-24 13:33:09.067  INFO 1 --- [           main] c.xumiao.springboot.docker.Application   : No active profile set, falling back to default profiles: default
2019-10-24 13:33:10.335  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2019-10-24 13:33:10.374  INFO 1 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2019-10-24 13:33:10.374  INFO 1 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.26]
2019-10-24 13:33:10.525  INFO 1 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2019-10-24 13:33:10.525  INFO 1 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1384 ms
2019-10-24 13:33:10.723  INFO 1 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2019-10-24 13:33:10.883  INFO 1 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2019-10-24 13:33:10.886  INFO 1 --- [           main] c.xumiao.springboot.docker.Application   : Started Application in 2.279 seconds (JVM running for 2.619)

我们通过docker ps查看一下容器运行情况：

docker psCONTAINER ID        IMAGE                         COMMAND                  CREATED             STATUS              PORTS                    NAMES
9a8a14b6d1ec        springio/spring-boot-docker   "java -cp app:app/li…"   4 minutes ago       Up 4 minutes        0.0.0.0:8080->8080/tcp   elegant_goldwasser

接着在浏览器访问http://localhost:8080可以看到“Hello Docker World”结果，大功告成！

参考资料

https://spring.io/guides/gs/spring-boot-Docker/

https://lw900925.github.io/docker/docker-springboot.html