Maven 简明教程

Maven - Snapshots

大型软件应用程序通常包含多个模块,在多个团队处理同一应用程序的不同模块时,这种情况很常见。例如,假设有一个团队正在处理应用程序的前端,作为 app-ui 项目(app-ui.jar:1.0),并且他们正在使用 data-service 项目(data-service.jar:1.0)。

现在可能发生的情况是,负责 data-service 的团队正在快速修复 bug 或进行增强,他们几乎每隔一天就会向远程存储库发布库。

现在,如果 data-service 团队每隔一天上传一个新版本,那么将会出现以下问题 −

  1. data-service 团队应在每次发布更新代码后告知 app-ui 团队。

  2. app-ui 团队需要定期更新其 pom.xml 以获取更新的版本。

为了处理此类情况, SNAPSHOT 的概念便应运而生。

What is SNAPSHOT?

SNAPSHOT 是一个特殊版本,它表示当前开发副本。与常规版本不同,Maven 会在远程存储库中为每次构建检查新的 SNAPSHOT 版本。

现在,data-service 团队将每次向存储库发布更新的代码的 SNAPSHOT,比如 data-service:1.0-SNAPSHOT,替换旧的 SNAPSHOT jar。

Snapshot vs Version

对于版本,如果 Maven 曾经下载过提到的版本,比如 data-service:1.0,它将永远不会尝试下载存储库中可用的较新的 1.0。要下载更新的代码,data-service 版本应升级到 1.1。

对于 SNAPSHOT,Maven 将每次 app-ui 团队构建其项目时自动获取最新的 SNAPSHOT(data-service:1.0-SNAPSHOT)。

app-ui pom.xml

app-ui 项目使用 data-service 1.0-SNAPSHOT。

<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>app-ui</groupId>
   <artifactId>app-ui</artifactId>
   <version>1.0</version>
   <packaging>jar</packaging>
   <name>health</name>
   <url>http://maven.apache.org</url>
   <properties>
      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
   </properties>
   <dependencies>
      <dependency>
      <groupId>data-service</groupId>
         <artifactId>data-service</artifactId>
         <version>1.0-SNAPSHOT</version>
         <scope>test</scope>
      </dependency>
   </dependencies>
</project>

data-service pom.xml

data-service 项目对每一次轻微的变更发布1.0-SNAPSHOT。

<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>data-service</groupId>
   <artifactId>data-service</artifactId>
   <version>1.0-SNAPSHOT</version>
   <packaging>jar</packaging>
   <name>health</name>
   <url>http://maven.apache.org</url>
   <properties>
      <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
   </properties>
</project>

尽管对于 SNAPSHOT,Maven 会在每天自动提取最新的 SNAPSHOT,但你可以通过任何 Maven 命令使用 -U 转换强制 Maven 下载最新的快照构建。

mvn clean package -U

让我们打开命令控制台,进入 C:\ > MVN > app-ui 目录并执行以下 mvn 命令。

C:\MVN\app-ui>mvn clean package -U

Maven 会在下载 data-service 的最新 SNAPSHOT 后开始构建项目。

[INFO] Scanning for projects...
[INFO]--------------------------------------------
[INFO] Building consumerBanking
[INFO]    task-segment: [clean, package]
[INFO]--------------------------------------------
[INFO] Downloading data-service:1.0-SNAPSHOT
[INFO] 290K downloaded.
[INFO] [clean:clean {execution: default-clean}]
[INFO] Deleting directory C:\MVN\app-ui\target
[INFO] [resources:resources {execution: default-resources}]

[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources,
i.e. build is platform dependent!

[INFO] skip non existing resourceDirectory C:\MVN\app-ui\src\main\resources
[INFO] [compiler:compile {execution:default-compile}]
[INFO] Compiling 1 source file to C:\MVN\app-ui\target\classes
[INFO] [resources:testResources {execution: default-testResources}]

[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources,
i.e. build is platform dependent!

[INFO] skip non existing resourceDirectory C:\MVN\app-ui\src\test\resources
[INFO] [compiler:testCompile {execution: default-testCompile}]
[INFO] Compiling 1 source file to C:\MVN\app-ui\target\test-classes
[INFO] [surefire:test {execution: default-test}]
[INFO] Surefire report directory: C:\MVN\app-ui\target\
surefire-reports

--------------------------------------------------
 T E S T S
--------------------------------------------------

Running com.companyname.bank.AppTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.027 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

[INFO] [jar:jar {execution: default-jar}]
[INFO] Building jar: C:\MVN\app-ui\target\
app-ui-1.0-SNAPSHOT.jar
[INFO]--------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO]--------------------------------------------------------
[INFO] Total time: 2 seconds
[INFO] Finished at: 2015-09-27T12:30:02+05:30
[INFO] Final Memory: 16M/89M
[INFO]------------------------------------------------------------------------