大型软件应用程序通常由多个模块组成，通常情况下，多个团队正在处理同一应用程序的不同模块.例如，考虑一个团队正在作为app-ui项目(app-ui.jar:1.0)在应用程序的前端工作，他们正在使用数据服务项目(data-service.jar:1.0).
现在可能会发生从事数据服务工作的团队正在快速修复错误或增强功能，并且他们几乎每隔一天就将库发布到远程存储库.
现在，如果数据服务团队每隔一天上传一个新版本，则会出现以下问题 :
数据服务团队应该在每次发布更新代码时告诉app-ui团队.
app-ui团队需要定期更新他们的pom.xml获取更新版本.
为了处理这种情况， SNAPSHOT 概念发挥作用.
SNAPSHOT是一个特殊版本，表示当前的开发副本.与常规版本不同，Maven会在每个版本的远程存储库中检查新的SNAPSHOT版本.
现在数据服务团队每次都会向存储库发布其更新代码的SNAPSHOT，比如数据 - service:1.0-SNAPSHOT，替换旧的SNAPSHOT jar.
如果是Version，如果Maven下载了上述版本，说数据服务:1.0，它永远不会尝试下载存储库中可用的新1.0.要下载更新的代码，数据服务版本将升级到1.1.
如果是SNAPSHOT，Maven将每次自动获取最新的SNAPSHOT(数据服务:1.0-SNAPSHOT) app-ui团队建立他们的项目.
app-ui 项目正在使用1.0 -SNAPSHOT数据服务.
<project xmlns = "http://maven.apache.org/POM/4.0.0" xmlns:xsi = "https://img01.yuandaxia.cn/Content/img/tutorials/maven/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>
数据服务项目正在发布1.0-每次轻微更改都会发生快照.
<project xmlns = "http://maven.apache.org/POM/4.0.0" xmlns:xsi = "https://img01.yuandaxia.cn/Content/img/tutorials/maven/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>
虽然在SNAPSHOT的情况下，Maven每天自动获取最新的SNAPSHOT，但您可以强制maven使用-U开关下载最新的快照构建maven命令.
mvn clean package -U
让我们打开命令控制台，转到 C:\> MVN> app-ui 目录并执行以下 mvn 命令.
C:\MVN\app-ui>mvn clean package -U
Maven将在之后开始构建项目下载最新的SNAPSHOT数据服务.
[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]------------------------------------------------------------------------------
