这是一个最简单的Maven项目，只有一个主类输出一句话，使用maven命令打包出jar包。
public class MainClass {
public static void main(String[] args) {
System.out.println("hello world！");
}
}
<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>org.example</groupId>
<artifactId>JVMDemo</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>jar</packaging>
<name>JVMDemo</name>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
<dependencyManagement>
<dependencies>
</dependencies>
</dependencyManagement>
<build>
<pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
<plugins>
<plugin>
<!-- Build an executable JAR -->
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>3.1.0</version>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<classpathPrefix>lib/</classpathPrefix>
<mainClass>MainClass</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
</plugins>
</pluginManagement>
</build>
</project>
Docker镜像最基本的要求就是需要有个Dockerfile文件，在这里面编写对应的依赖镜像、环境和启动参数等信息。
第一行是说要依赖store/oracle/serverjre:8镜像，这其实是Oracle JDK 8的一个官方镜像，第二行则是把当前目录的JVMDemo-1.0-SNAPSHOT.jar复制到容器内部的/opt/jar目录下，jar包就是上面maven项目生成的，最后一行是一条执行命令，也就是启动这个jar包。
FROM store/oracle/serverjre:8
COPY JVMDemo-1.0-SNAPSHOT.jar /opt/jar/JVMDemo-1.0-SNAPSHOT.jar
CMD java -jar /opt/jar/JVMDemo-1.0-SNAPSHOT.jar
执行docker image build -t hello-java:latest .命令来根据Dockerfile构建镜像，注意其中的.是表明在当前路径作为根路径，-t则是添加标签。
E:\docker\java-demo>docker image build -t hello-java:latest .
[+] Building 0.7s (7/7) FINISHED
=> [internal] load build definition from Dockerfile 0.1s
=> => transferring dockerfile: 181B 0.0s
=> [internal] load .dockerignore 0.1s
=> => transferring context: 2B 0.0s
=> [internal] load metadata for docker.io/store/oracle/serverjre:8 0.0s
=> [internal] load build context 0.2s
=> => transferring context: 3.24kB 0.0s
=> [1/2] FROM docker.io/store/oracle/serverjre:8 0.3s
=> => resolve docker.io/store/oracle/serverjre:8 0.0s
=> [2/2] COPY JVMDemo-1.0-SNAPSHOT.jar /opt/jar/JVMDemo-1.0-SNAPSHOT.jar 0.1s
=> exporting to image 0.1s
=> => exporting layers 0.1s
=> => writing image sha256:6de2db209e0e4175a00d99d91abb048ed3ca64da48a648e5620b99cc67fd6c66 0.0s
=> => naming to docker.io/library/hello-java:latest
可以查看本地镜像会有刚才生成的hello-java
E:\docker\java-demo>docker image ls
REPOSITORY TAG IMAGE ID CREATED SIZE
hello-java latest 6de2db209e0e 16 seconds ago 290MB
运行该镜像会输出对应信息，可以看到本质上就是只将所需要的环境集成在镜像内，以减小镜像大小，加快构建速度，响应的启动速度也会更快，占用资源也会更少。
E:\docker\java-demo>docker run --name java hello-java
hello world!
Docker Hub是类似于Github一样的一个远程镜像仓库，里面有很多官方的镜像，也可以推送自己的上去。首先要登录自己的Doker Hub账号。
E:\docker\java-demo>docker login
Login with your Docker ID to push and pull images from Docker Hub. If you don't have a Docker ID, head over to https://hub.docker.com to create one.
Username: test
Password:
需要对镜像打标签，最后一段的格式是Docker Hub用户名/仓库名:标签名，如果没有对应仓库会自动创建一个仓库。
docker tag hello-java:latest nemohalf/hello-java:latest
最后使用push命令推送到远程仓库，下一次使用时，直接拉取到本地就可以。
E:\docker\java-demo>docker push nemohalf/hello-java:latest
The push refers to repository [docker.io/nemohalf/hello-java]
154fc6c09dec: Pushed
945301b2fd91: Pushed
11e019486fcd: Pushed
5102fc2ee26e: Pushed
latest: digest: sha256:12af8b4c6d474189d00b8eb3e9cb1b56106db5488619b0592f89babffce2da60 size: 1160
maven还提供了docker构建的插件，只要添加下列配置即可把项目构建成镜像。
<plugin>
<groupId>com.spotify</groupId>
<artifactId>docker-maven-plugin</artifactId>
<version>1.2.2</version>
<configuration>
<!-- <dockerHost>http://localhost:2375</dockerHost>-->
<!--镜像名称-->
<imageName>spotify-docker-java</imageName>
<!--指定基础镜像-->
<baseImage>java</baseImage>
<!--ENTRYPOINT指令-->
<entryPoint>["java", "-jar", "/${project.build.finalName}.jar"]</entryPoint>
<resources>
<resource>
<targetPath>/</targetPath>
<!--用于指定需要复制的根目录-->
<directory>${project.build.directory}</directory>
<!--用于指定需要复制的文件-->
<include>${project.build.finalName}.jar</include>
</resource>
</resources>
</configuration>
</plugin>
运行mvn package docker:build就可以执行构建命令，注意最下面会有构建步骤，但是需要Docker引擎对外暴露2375端口，否则会提示无法连接。
D:\download\JVMDemo>mvn package docker:build
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building JVMDemo 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ JVMDemo ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory D:\download\JVMDemo\src\main\resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ JVMDemo ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ JVMDemo ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory D:\download\JVMDemo\src\test\resources
[INFO]
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ JVMDemo ---
[INFO] No sources to compile
[INFO]
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ JVMDemo ---
[INFO]
[INFO] --- maven-jar-plugin:3.1.0:jar (default-jar) @ JVMDemo ---
[INFO]
[INFO] --- docker-maven-plugin:1.2.2:build (default-cli) @ JVMDemo ---
[INFO] Using authentication suppliers: [ConfigFileRegistryAuthSupplier]
[INFO] Copying D:\download\JVMDemo\target\JVMDemo-1.0-SNAPSHOT.jar -> D:\download\JVMDemo\target\docker\JVMDemo-1.0-SNAPSHOT.jar
[INFO] Building image spotify-docker-java
Step 1/3 : FROM java
---> d23bdf5b1b1b
Step 2/3 : ADD /JVMDemo-1.0-SNAPSHOT.jar //
---> Using cache
---> bdba5da04d67
Step 3/3 : ENTRYPOINT ["java", "-jar", "/JVMDemo-1.0-SNAPSHOT.jar"]
---> Using cache
---> 785f5ba92d2d
ProgressMessage{id=null, status=null, stream=null, error=null, progress=null, progressDetail=null}
Successfully built 785f5ba92d2d
Successfully tagged spotify-docker-java:latest
[INFO] Built spotify-docker-java
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 20.828 s
[INFO] Finished at: 2021-01-05T11:09:56+08:00
[INFO] Final Memory: 24M/144M
[INFO] ------------------------------------------------------------------------