Maven 入门篇

Maven简介

    提供了项目构建、项目依赖解决方案。例如：jar包依赖，在没有maven之前，通常是在依赖包的官网进行下载，然后复制到lib目录下，人工去处理依赖和管理依赖，非常的麻烦，但是maven之后，只需要引入项目依赖包的坐标就可以自动下载依赖和管理依赖。    本章主要讲述maven的基本使用。具体可以参考：https://maven.apache.org/ 

下载&安装

下载地址：http://maven.apache.org/download.cgi 安装向导：http://maven.apache.org/install.html (包含了环境参数的配置)

关于安装需要注意的问题：1、本地仓库；默认安装本地仓库会安装在 **用户目录/.m2/repository**，2、全局配置/用户配置；1）全局配置：下载的包conf/settings.xml就是全局配置，一旦这里设置了，所有用户目录生效；2）用户配置：将conf/settings.xml copy到.m2/settings.xml 进行配置，只是作用在当前用户目录下；（建议使用）；

POM

POM: Project Object Model, maven是通过pom.xml来构建、管理项目的。该文件用于描述项目；

项目坐标

    如何唯一定位一个项目，就像我们的住宅门牌号码，通过省份、城市、街道、门牌号码等进行划分，然后进行定位。maven自己定了一套坐标用于唯一标识项目，通常称之为“**G**(groupId)**A**(artifactId)**V**(version)”。

• GAV

**groupId**: 一般标识公司的项目；例如：谷歌的账户项目；com.google.account, 推荐命名方式：公司.项目名；**artifactId**: 通常等价于模块，是项目的下一级，例如：账户的邮件模块,com.google.account.account-email, 推荐命名：项目名-模块名;**version**: 项目版本，只要有一套统一的版本管理就可以，不过需要特别注意的是SNAPSHOT（快照）版本；packaging: 打包方式，诸如：jar、pom、warclassifier: 附属构件，例如：spring-core-1.0.0.0-javadoc.jar，其中javadoc就是classifier生成的，不需要用户配置，通常是第三方插件设置的。默认打包：artifactId-version-[classifier].packaging, 例如：spring-core-1.0-SNAPSHOT.jar

• 如何管理

按照GAV坐标我们可以定位项目，但是这些项目是如何管理，并提供服务 ？1、本地仓库：local环境，也就是用户自己的本地环境，即：.m2/repository2、中央仓库：默认：https://repo1.maven.org/maven2/ ；当在项目中指定了依赖之后，maven会默认先从本地仓库下载，如果没有然后从中央仓库下载，下载完成之后，会存储到本地仓库，这样所有的项目就可以使用了，需要使用的地方，只需要申明依赖引用（后续介绍）；

基本使用

创建项目（骨架）

命令创建

mvn archetype:generate Choose a number: 6: Define value for property 'groupId': : study.wzp.mavenDefine value for property 'artifactId': : maven-helloDefine value for property 'version':  1.0-SNAPSHOT: :Define value for property 'package':  study.wzp.maven: : jarConfirm properties configuration:groupId: study.wzp.mavenartifactId: maven-helloversion: 1.0-SNAPSHOTpackage: jarY: : Y

使用m2eclipse(插件)

最终生成的目录结构：maven-study|--- src|--- --- main/java （存放java代码）|--- --- main/resources （存放资源配置文件）|--- --- test/java （存放单元测试代码）|--- --- test/resources （存放单元测试配置文件）|--- pom.xml （maven配置文件）

基本命令操作

clean

• mvn clean

[INFO] Scanning for projects...[WARNING] [WARNING] Some problems were encountered while building the effective model for study.wzp.maven:maven-hello:jar:1.0-SNAPSHOT[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-compiler-plugin is missing. @ line 43, column 15[WARNING] [WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.[WARNING] [WARNING] For this reason, future Maven versions might no longer support building such malformed projects.[WARNING] [INFO]                                                                         [INFO] ------------------------------------------------------------------------[INFO] Building maven-hello 1.0-SNAPSHOT[INFO] ------------------------------------------------------------------------[INFO] [INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ maven-hello ---[INFO] Deleting /Users/wangzhiping/idea-workspace/maven-study/target[INFO] ------------------------------------------------------------------------[INFO] BUILD SUCCESS[INFO] ------------------------------------------------------------------------[INFO] Total time: 0.361s[INFO] Finished at: Tue Aug 15 15:19:15 CST 2017[INFO] Final Memory: 6M/155M[INFO] ------------------------------------------------------------------------

mvn clean 目的是清楚target目录，使用maven-clean-plugin插件[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ maven-hello ---[INFO] Deleting /Users/wangzhiping/idea-workspace/maven-study/target

compile

• mvn compile

INFO] ------------------------------------------------------------------------[INFO] Building maven-hello 1.0-SNAPSHOT[INFO] ------------------------------------------------------------------------[INFO] [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-hello ---[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent![INFO] Copying 1 resource[INFO] [INFO] --- maven-compiler-plugin:2.5.1:compile (default-compile) @ maven-hello ---[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent![INFO] Compiling 1 source file to /Users/wangzhiping/idea-workspace/maven-study/target/classes[INFO] ------------------------------------------------------------------------[INFO] BUILD SUCCESS[INFO] ------------------------------------------------------------------------[INFO] Total time: 1.634s[INFO] Finished at: Tue Aug 15 15:21:23 CST 2017[INFO] Final Memory: 12M/155M[INFO] ------------------------------------------------------------------------

注意mvn compile执行是，首先是执行maven-resources-plugin,然后再执行maven-compiler-plugin插件，因为在编译时，可能会使用资源配置文件，因此需要先将资源配置文件也先引入进来，然后再编译，编译之后将class文件存放在：/Users/wangzhiping/idea-workspace/maven-study/target/classes （target/classes）

test

• mvn test

INFO] ------------------------------------------------------------------------[INFO] Building maven-hello 1.0-SNAPSHOT[INFO] ------------------------------------------------------------------------[INFO] [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-hello ---[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent![INFO] Copying 1 resource[INFO] [INFO] --- maven-compiler-plugin:2.5.1:compile (default-compile) @ maven-hello ---[INFO] Nothing to compile - all classes are up to date[INFO] [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ maven-hello ---[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent![INFO] Copying 1 resource[INFO] [INFO] --- maven-compiler-plugin:2.5.1:testCompile (default-testCompile) @ maven-hello ---[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent![INFO] Compiling 1 source file to /Users/wangzhiping/idea-workspace/maven-study/target/test-classes[INFO] [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ maven-hello ---[INFO] Surefire report directory: /Users/wangzhiping/idea-workspace/maven-study/target/surefire-reports------------------------------------------------------- T E S T S-------------------------------------------------------Running study.wzp.maven.AppTestTests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.083 secResults :Tests run: 1, Failures: 0, Errors: 0, Skipped: 0[INFO] ------------------------------------------------------------------------[INFO] BUILD SUCCESS[INFO] ------------------------------------------------------------------------[INFO] Total time: 2.699s[INFO] Finished at: Tue Aug 15 15:24:04 CST 2017[INFO] Final Memory: 13M/165M[INFO] ------------------------------------------------------------------------

执行mvn test时，会执行1,maven-resources-plugin: resources2,maven-compiler-plugin: compile3,maven-resources-plugin: testResources;4,mavne-compiler-plugin: testCompile;5,maven-surefire-plugin: test;其实很容易理解，单元测试依赖于主项目代码，因此主项目代码需要先加载资源、编译；然后再执行单元测试，因此在执行单元测试时，再加载资源、编译；最后执行单元测试。

package

• mvn package

[INFO] ------------------------------------------------------------------------[INFO] Building maven-hello 1.0-SNAPSHOT[INFO] ------------------------------------------------------------------------[INFO] [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-hello ---[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent![INFO] Copying 1 resource[INFO] [INFO] --- maven-compiler-plugin:2.5.1:compile (default-compile) @ maven-hello ---[INFO] Nothing to compile - all classes are up to date[INFO] [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ maven-hello ---[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent![INFO] Copying 1 resource[INFO] [INFO] --- maven-compiler-plugin:2.5.1:testCompile (default-testCompile) @ maven-hello ---[INFO] Nothing to compile - all classes are up to date[INFO] [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ maven-hello ---[INFO] Surefire report directory: /Users/wangzhiping/idea-workspace/maven-study/target/surefire-reports------------------------------------------------------- T E S T S-------------------------------------------------------Running study.wzp.maven.AppTestTests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.074 secResults :Tests run: 1, Failures: 0, Errors: 0, Skipped: 0[INFO] [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ maven-hello ---[INFO] Building jar: /Users/wangzhiping/idea-workspace/maven-study/target/maven-hello-1.0-SNAPSHOT.jar[INFO] ------------------------------------------------------------------------[INFO] BUILD SUCCESS[INFO] ------------------------------------------------------------------------[INFO] Total time: 1.695s[INFO] Finished at: Tue Aug 15 15:28:33 CST 2017[INFO] Final Memory: 8M/155M[INFO] ------------------------------------------------------------------------

执行package，会先执行test阶段，然后再使用maven-jar-plugin打包，并输出到:target/[INFO] Building jar: /Users/wangzhiping/idea-workspace/maven-study/target/maven-hello-1.0-SNAPSHOT.jar (jar包的命名规则就是上文提到的默认命名)

install

• mvn install

[INFO] ------------------------------------------------------------------------[INFO] Building maven-hello 1.0-SNAPSHOT[INFO] ------------------------------------------------------------------------[INFO] [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ maven-hello ---[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent![INFO] Copying 1 resource[INFO] [INFO] --- maven-compiler-plugin:2.5.1:compile (default-compile) @ maven-hello ---[INFO] Nothing to compile - all classes are up to date[INFO] [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ maven-hello ---[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent![INFO] Copying 1 resource[INFO] [INFO] --- maven-compiler-plugin:2.5.1:testCompile (default-testCompile) @ maven-hello ---[INFO] Nothing to compile - all classes are up to date[INFO] [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ maven-hello ---[INFO] Surefire report directory: /Users/wangzhiping/idea-workspace/maven-study/target/surefire-reports------------------------------------------------------- T E S T S-------------------------------------------------------Running study.wzp.maven.AppTestTests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.062 secResults :Tests run: 1, Failures: 0, Errors: 0, Skipped: 0[INFO] [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ maven-hello ---[INFO] [INFO] --- maven-install-plugin:2.4:install (default-install) @ maven-hello ---[INFO] Installing /Users/wangzhiping/idea-workspace/maven-study/target/maven-hello-1.0-SNAPSHOT.jar to /Users/wangzhiping/.m2/repository/study/wzp/maven/maven-hello/1.0-SNAPSHOT/maven-hello-1.0-SNAPSHOT.jar[INFO] Installing /Users/wangzhiping/idea-workspace/maven-study/pom.xml to /Users/wangzhiping/.m2/repository/study/wzp/maven/maven-hello/1.0-SNAPSHOT/maven-hello-1.0-SNAPSHOT.pom[INFO] ------------------------------------------------------------------------[INFO] BUILD SUCCESS[INFO] ------------------------------------------------------------------------[INFO] Total time: 1.693s[INFO] Finished at: Tue Aug 15 15:31:08 CST 2017[INFO] Final Memory: 9M/155M[INFO] ------------------------------------------------------------------------

mvn install 的目的是将当前项目安装到本地仓库，这样本地的其他项目都可以引用；wangzhiping@wangzhipingdeMacBook-Pro ~/.m2/repository/study/wzp/maven/maven-hello/1.0-SNAPSHOT-rw-r--r--  1 wangzhiping  staff   195B  8 15 15:31 _remote.repositories-rw-r--r--  1 wangzhiping  staff   2.9K  8 15 15:30 maven-hello-1.0-SNAPSHOT.jar-rw-r--r--  1 wangzhiping  staff   1.8K  8 15 15:30 maven-hello-1.0-SNAPSHOT.pom-rw-r--r--  1 wangzhiping  staff   706B  8 15 15:31 maven-metadata-local.xml可以在.m2/repository查看已经安装。

总结

| --- clean (use maven-clean-plugin)| --- --- delete target/| --- install (use maven-install-plugin)| --- --- package (use maven-jar-plugin)| --- --- --- test (use maven-surefire-plugin)| --- --- --- --- compile (use maven-compile-plugin)| --- --- --- --- --- resources: resources| --- --- --- --- --- compiler: compile| --- --- --- --- resources: testResources| --- --- --- --- compiler: testCompile (to target/test-classes)| --- --- --- --- surefire: test| --- --- install (install to .m2/repository)

配置

<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>  <!--    项目坐标，GAV（groupId, ArtifactId, Version）- Packaging, Classifier（用于构建附属构件的，例如:javadoc.jar，sources.jar之类的）    最佳实践命名：    groupId: 一般是一家公司的项目名，例如：eleme的运单项目；me.ele.order    artifactId: 一般是项目的模块；例如：支付模块; order-payment，格式：[App].[Module]    version: 版本，一般是遵循一套版本管理模范，特别需要注意的是SNAPSHOT；    packaging: jar, pom, war 默认命名是: artifactId-version-[classifier].jar,例如：maven-hello-1.0-SNAPSHOT-javadoc.jar  -->  <groupId>study.wzp.maven</groupId>  <artifactId>maven-hello</artifactId>  <version>1.0-SNAPSHOT</version>  <packaging>jar</packaging>  <name>maven-hello</name>  <!-- 依赖管理 -->  <dependencies>    <!-- 依赖junit，使用GAV定位 -->    <dependency>      <groupId>junit</groupId>      <artifactId>junit</artifactId>      <version>4.10</version>      <scope>test</scope>    </dependency>  </dependencies></project>

参考：

[1] https://maven.apache.org/guides/index.html