Maven 快照(SNAPSHOT)

Maven 快照(SNAPSHOT)一个大型的软件应用通常包含多个模块，并且通常的场景是多个团队开发同一应用的不同模块。举个例子，设想一个团队开发应用的前端，项目为 app-ui(app-ui.jar:





1.0)，而另一个团队开发应用的后台，使用的项目是 data-service(data-service.jar:





1.0)。现在可能出现的情况是开发 data-service 的团队正在进行快节奏的 bug 修复或者项目改进，并且他们几乎每隔一天就要发布库到远程仓库。现在如果 data-service 团队每隔一天上传一个新版本，那么将会出现下面的问题：data-service 团队每次发布更新的代码时都要告知 app-ui 团队。app-ui 团队需要经常地更新他们 pom.xml 文件到最新版本。为了解决这种情况，快照的概念派上了用场。什么是快照?快照是一种特殊的版本，指定了某个当前的开发进度的副本。不同于常规的版本，Maven 每次构建都会在远程仓库中检查新的快照。现在 data-service 团队会每次发布更新代码的快照到仓库中，比如说 data-service:





1.0-SNAPSHOT 来替代旧的快照 jar 包。项目快照 vs 版本对于版本，如果 Maven 以前下载过指定的版本文件，比如说 data-service:





1.0，Maven 将不会再从仓库下载新的可用的 1.0 文件。若要下载更新的代码，data-service 的版本需要升到1.1。快照的情况下，每次 app-ui 团队构建他们的项目时，Maven 将自动获取最新的快照(data-service:





1.0-SNAPSHOT)。app-ui 项目的 pom.xml 文件app-ui 项目使用的是 data-service 项目的 1.0 快照。<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/4.0.0http:





//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 项目的 pom.xml 文件data-service 项目为每次小的改动发布 1.0 快照。<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/4.0.0http:





//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，快照的情况下，Maven 在日常工作中会自动获取最新的快照， 你也可以在任何 maven 命令中使用 -U 参数强制 maven 现在最新的快照构建。mvn clean package -U让我们打开命令控制台，去到 C:





\ > MVN > app-ui 目录，然后执行下面的 mvn 命令。C:





\MVN\app-ui>mvn clean package -UMaven 将在下载 data-service 最新的快照之后，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.AppTestTests run:





1, Failures:





0, Errors:





0, Skipped:





0, Time elapsed:





0.027 secResults :





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:





Tue Jul 10 16:





52:





18 IST 2012[INFO] Final Memory:





16M/89M[INFO] ------------------------------------------------------------------------