本文演示瞭如何用 Docker、Gradle 來構建、執行、釋出來一個 Spring Boot 應用。

Docker 簡介

Docker是一個 Linux 容器管理工具包，具備“社交”方面，允許使用者釋出容器的 image (映象)，並使用別人釋出的 image。Docker image 是用於執行容器化程序的方案，在本文中，我們將構建一個簡單的 Spring Boot 應用程式。

有關 Docker 的詳細介紹，可以移步至《簡述 Docker》

前置條件

• Docker 最新版。有關 Docker 在的安裝，可以參閱《Docker 在 CentOS 下的安裝、使用》。 如果你的電腦不是 Linux 系統，最好裝個虛擬機器，在虛擬機器裡面裝個 Linux ，因為 Docker 的依賴 Linux。

用 Gradle 構建專案

建立目錄結構

專案的目錄結構因符合 Gradle 的約定。

在 *nix 系統下執行mkdir -p src/main/java/docker_spring_boot,生產如下結構 :

└── src
 └── main
 └── java
 └── com
 └── waylau
 └── docker_spring_boot

建立 Gradle 構建檔案

build.gradle

buildscript {
 repositories {
 mavenCentral()
 }
 dependencies {
 classpath('org.springframework.boot:spring-boot-gradle-plugin:1.3.3.RELEASE'
 
)
// tag::build[]
 classpath('se.transmode.gradle:gradle-docker:1.2')
// end::build[]
 }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'
apply plugin: 'spring-boot' // tag::plugin[]
apply plugin: 'docker' // end::plugin[] // This is used as the docker image prefix (org) group = 'gregturn'
 


jar {
 baseName = 'docker-spring-boot-gradle'
 version = '1.0.0'
}

// tag::task[] task buildDocker(type: Docker, dependsOn: build) {
 push = true
 applicationName = jar.baseName
 dockerfile = file('src/main/docker/Dockerfile')
 doFirst {
 copy {
 from jar
 into stageDir
 }
 }
}
// end::task[]

repositories {
 mavenCentral()
}

sourceCompatibility = 1.8
targetCompatibility = 1.8

dependencies {
 compile("org.springframework.boot:spring-boot-starter-web") 
 testCompile("org.springframework.boot:spring-boot-starter-test")
}

task wrapper(type: Wrapper) {
 gradleVersion = '2.3'
}

編寫 Spring Boot 應用

編寫一個簡單的 Spring Boot 應用 ：

src/main/java/com/waylau/docker_spring_boot/Application.java:

package com.waylau.docker_spring_boot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * 主應用入口
 * @author <a href="http://waylau.com">waylau.com</a>
 * @date 2016年3月19日
 */ @SpringBootApplication @RestController public class Application {

 @RequestMapping("/")
 public String home() {
 return "Hello Docker World."
 + "<br />Welcome to <a href='http://waylau.com'>waylau.com</a></li>";
 }

 public static void main(String[] args) {
 SpringApplication.run(Application.class, args);
 }

}

解釋下上面的程式碼：

• 類用@SpringBootApplication@RestController標識,可用 Spring MVC 來處理 Web 請求。
• @RequestMapping將/對映到home()，並將"Hello Docker World" 文字作為響應。
• main()方法使用 Spring Boot 的SpringApplication.run()方法來啟動應用。

執行程式

使用 Gradle

編譯：

gradle build 

執行：

java -jar build/libs/docker-spring-boot-gradle-1.0.0.jar

訪問專案

如果程式正確執行，瀏覽器訪問http://localhost:8080/，可以看到頁面 “Hello Docker World.” 字樣。

將專案容器化

Docker 使用Dockerfile檔案格式來指定 image 層，

建立檔案src/main/docker/Dockerfile:

FROM frolvlad/alpine-oraclejdk8:slim
VOLUME /tmp
ADD docker-spring-boot-gradle-1.0.0.jar app.jar
ENTRYPOINT ["java","-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]

解釋下這個配置檔案：

• VOLUME指定了臨時檔案目錄為/tmp。其效果是在主機/var/lib/docker目錄下建立了一個臨時檔案，並連結到容器的/tmp。改步驟是可選的，如果涉及到檔案系統的應用就很有必要了。/tmp目錄用來持久化到 Docker 資料資料夾，因為 Spring Boot 使用的內嵌 Tomcat 容器預設使用/tmp作為工作目錄
• 專案的 jar 檔案作為 "app.jar" 新增到容器的
• ENTRYPOINT執行專案 app.jar。為了縮短Tomcat 啟動時間，新增一個系統屬性指向 "/dev/urandom" 作為 Entropy Source

構建 Docker Image

執行構建成為 docker image:

gradle build buildDocker

執行

執行 Docker Image

docker run -p 8080:8080 -t waylau/docker-spring-boot-gradle

[[email protected] spring-boot]# docker run -p 8080:8080 -t waylau/docker-spring-boot-gradle

 . ____ _ __ _ _
 /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/ ___)| |_)| | | | | || (_| | ) ) ) )
 ' |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot :: (v1.3.3.RELEASE)

2016-03-20 08:45:51.276 INFO 1 --- [ main] c.waylau.docker_spring_boot.Application : Starting Application v1.0.0 on 048fb623038f with PID 1 (/app.jar started by root in /)
2016-03-20 08:45:51.289 INFO 1 --- [ main] c.waylau.docker_spring_boot.Application : No active profile set, falling back to default profiles: default
2016-03-20 08:45:51.722 INFO 1 --- [ main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot[email protected]669af5fc: startup date [Sun Mar 20 08:45:51 GMT 2016]; root of context hierarchy
2016-03-20 08:45:54.874 INFO 1 --- [ main] o.s.b.f.s.DefaultListableBeanFactory : Overriding bean definition for bean 'beanNameViewResolver' with a different definition: replacing [Root bean: class [null]; scope=; abstract=false; lazyInit=false; autowireMode=3; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration$WhitelabelErrorViewConfiguration; factoryMethodName=beanNameViewResolver; initMethodName=null; destroyMethodName=(inferred); defined in class path resource [org/springframework/boot/autoconfigure/web/ErrorMvcAutoConfiguration$WhitelabelErrorViewConfiguration.class]] with [Root bean: class [null]; scope=; abstract=false; lazyInit=false; autowireMode=3; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapter; factoryMethodName=beanNameViewResolver; initMethodName=null; destroyMethodName=(inferred); defined in class path resource [org/springframework/boot/autoconfigure/web/WebMvcAutoConfiguration$WebMvcAutoConfigurationAdapter.class]]
2016-03-20 08:45:57.893 INFO 1 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)
2016-03-20 08:45:57.982 INFO 1 --- [ main] o.apache.catalina.core.StandardService : Starting service Tomcat
2016-03-20 08:45:57.984 INFO 1 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/8.0.32
2016-03-20 08:45:58.473 INFO 1 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext
2016-03-20 08:45:58.473 INFO 1 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 6877 ms
2016-03-20 08:45:59.672 INFO 1 --- [ost-startStop-1] o.s.b.c.e.ServletRegistrationBean : Mapping servlet: 'dispatcherServlet' to [/]
2016-03-20 08:45:59.695 INFO 1 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean : Mapping filter: 'characterEncodingFilter' to: [/*]
2016-03-20 08:45:59.701 INFO 1 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2016-03-20 08:45:59.703 INFO 1 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2016-03-20 08:45:59.703 INFO 1 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean : Mapping filter: 'requestContextFilter' to: [/*]
2016-03-20 08:46:00.862 INFO 1 --- [ main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot[email protected]669af5fc: startup date [Sun Mar 20 08:45:51 GMT 2016]; root of context hierarchy
2016-03-20 08:46:01.166 INFO 1 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/]}" onto public java.lang.String com.waylau.docker_spring_boot.Application.home()
2016-03-20 08:46:01.189 INFO 1 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2016-03-20 08:46:01.190 INFO 1 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2016-03-20 08:46:01.302 INFO 1 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2016-03-20 08:46:01.302 INFO 1 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2016-03-20 08:46:01.438 INFO 1 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2016-03-20 08:46:01.833 INFO 1 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup
2016-03-20 08:46:02.332 INFO 1 --- [ main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)
2016-03-20 08:46:02.343 INFO 1 --- [ main] c.waylau.docker_spring_boot.Application : Started Application in 13.194 seconds (JVM running for 15.828) 

訪問專案

如果程式正確執行，瀏覽器訪問http://localhost:8080/，可以看到頁面 “Hello Docker World.” 字樣。

推送 image 到 Docker Hub

首先，你在 Docker Hub 要有註冊賬號，且建立了相應的庫；

其次，docker 推送前，先要登入，否則報unauthorized: access to the requested resource is not authorized的錯誤

執行：

docker login

輸出為：

[[email protected] spring-boot]# docker login
Username: waylau
Password: 
Email: [email protected]
WARNING: login credentials saved in /root/.docker/config.json
Login Succeeded

執行推送

docker push waylau/docker-spring-boot-gradle

[[email protected] spring-boot]# docker push waylau/docker-spring-boot-gradle
The push refers to a repository [docker.io/waylau/docker-spring-boot-gradle]
751d29eef02e: Layer already exists 4da3741f39c7: Pushed 
5f70bf18a086: Layer already exists 7e4d0cb13643: Layer already exists 8f045733649f: Layer already exists 
latest: digest: sha256:eb4d5308ba1bb27489d808279e74784bda6761b3574f4298d746abba59b35164 size: 9415 

映象加速器

Docker Hub 在國外，有時候拉取 Image 極其緩慢，可以使用國內的映象來實現加速

阿里雲

echo "DOCKER_OPTS=\"--registry-mirror=https://yourlocation.mirror.aliyuncs.com\"" | sudo tee -a /etc/default/docker
sudo service docker restart

DaoCloud

sudo echo “DOCKER_OPTS=\”\$DOCKER_OPTS –registry-mirror=http://your-id.m.daocloud.io -d\”” >> /etc/default/docker
sudo service docker restart

原始碼

獲取專案映象， 執行

docker pull waylau/docker-spring-boot-gradle