第一个简单的maven项目

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学习一个新的东西，最快的方式就是实践。所以我们也不用多说什么了，直接拿一个项目来练手。下面的整理取自maven权威指南，在一堆maven资料中，我觉得这本书写的最好。

简介

我们介绍一个用Maven Archetype插件从空白开始创建的简单项目。当你跟着这个简单项目的开发过程,你会看到这个简单的应用给我们提供了介绍Maven核心概念的机会。
在你能开始使用Maven做复杂的,多模块的构建之前,我们需要从基础开始。如果你之前用过Maven,你将会注意到这里很好的照顾到了细节。你的构建倾向于“只要能工作”,只有当你需要编写插件来自定义默认行为的时候,才需要深入Maven的细节。另一方面,当你需要深入Maven细节的时候,对Maven核心概念的彻底理解是至关重要的。本章致力于为你介绍一个尽可能简单的Maven项目,然后介绍一些使Maven 成为一个可靠的构建平台的核心概念。看过这个例子之后,你将会对构建生命周期 (build lifecycle),Maven仓库 (repositories),依赖管理 (dependency management)和项目对象模型 (Project Object Model)有一个基本的理解。

1，创建一个简单的项目

在这里我使用eclipse来生成一个项目，然后修改POM的文件的默认依赖，然后修改项目的目录文件，形成一个新的项目。OK，下面是该项目的项目结构，这里也贴出POM文件。

<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>org.linkinpark.maven</groupId><artifactId>linkinMaven</artifactId><version>0.0.1-SNAPSHOT</version><packaging>jar</packaging><name>linkinMaven</name><url>http://maven.apache.org</url><properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version><scope>test</scope></dependency><dependency><groupId>org.hamcrest</groupId><artifactId>hamcrest-junit</artifactId><version>2.0.0.0</version><scope>test</scope></dependency></dependencies></project>

2，构建一个简单的项目

这里我们暂时写2个简单的Java文件，一个是源文件，一个是测试文件，下面是代码。

package org.linkinpark.maven.linkinMaven;public class HelloLinkin{public static void main(String[] args){System.out.println("hello，LinkinPark。。。");}}

package org.linkinpark.maven.linkinMaven;import org.junit.Assert;import org.junit.Test;public class HelloTest{@Testpublic void test(){Assert.assertEquals("字符串的结果应该是LinkinPark", "LinkinPark", "LinkinPark");}}

写完代码之后我们在POM文件上右键然后run as maven install，控制台输出如下：

[INFO] Scanning for projects...[INFO]                                                                         [INFO] ------------------------------------------------------------------------[INFO] Building linkinMaven 0.0.1-SNAPSHOT[INFO] ------------------------------------------------------------------------[INFO] [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ linkinMaven ---[INFO] Using 'UTF-8' encoding to copy filtered resources.[INFO] Copying 0 resource[INFO] [INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ linkinMaven ---[INFO] Nothing to compile - all classes are up to date[INFO] [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ linkinMaven ---[INFO] Using 'UTF-8' encoding to copy filtered resources.[INFO] Copying 0 resource[INFO] [INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ linkinMaven ---[INFO] Nothing to compile - all classes are up to date[INFO] [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ linkinMaven ---[INFO] Surefire report directory: /Users/LinkinPark/WorkSpace/linkinMaven/target/surefire-reports------------------------------------------------------- T E S T S-------------------------------------------------------Running org.linkinpark.maven.linkinMaven.HelloTestTests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.052 secResults :Tests run: 1, Failures: 0, Errors: 0, Skipped: 0[INFO] [INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ linkinMaven ---[INFO] [INFO] --- maven-install-plugin:2.4:install (default-install) @ linkinMaven ---[INFO] Installing /Users/LinkinPark/WorkSpace/linkinMaven/target/linkinMaven-0.0.1-SNAPSHOT.jar to /Users/LinkinPark/repository/org/linkinpark/maven/linkinMaven/0.0.1-SNAPSHOT/linkinMaven-0.0.1-SNAPSHOT.jar[INFO] Installing /Users/LinkinPark/WorkSpace/linkinMaven/pom.xml to /Users/LinkinPark/repository/org/linkinpark/maven/linkinMaven/0.0.1-SNAPSHOT/linkinMaven-0.0.1-SNAPSHOT.pom[INFO] ------------------------------------------------------------------------[INFO] BUILD SUCCESS[INFO] ------------------------------------------------------------------------[INFO] Total time: 1.493 s[INFO] Finished at: 2016-02-17T00:21:24+08:00[INFO] Final Memory: 10M/309M[INFO] ------------------------------------------------------------------------

最后的结果build success，OK，没有问题。注意的是上面的测试tests命令之后的install，控制台明确的告诉了maven默认将我们编译过后生成的这个jar包放到了什么位置上面。

我们切到maven给我们安装的jar所在文件夹下，使用Java -cp命令来执行jar包看下效果：

3，POM文件的说明

在前面第一点上我已经贴出了POM文件。这个pom.xml文件是你将会面对的Maven项目中最基础的POM,一般来说一个POM文件会复杂得多:定义多个依赖,自定义插件行为。最开始的几个元素——groupId,artifactId, packaging, version——是Maven的坐标(coordinates),它们唯一标识了一个项目。name和url是POM提供的描述性元素,它们给人提供了可阅读的名字,将一个项目关联到了项目web站点。最后,dependencies元素定义了一个单独的,测试范围(test-scoped)依赖,依赖于称为JUnit的单元测试框架。关于POM，记住最重要的一句话，pom.xml是一个让Maven跑起来的文件。
当Maven运行的时候,它是根据项目的pom.xml里设置的组合来运行的,一个最上级的POM定义了Maven的安装目录,在这个目录中全局的默认值被定义了,(可能)还有一些用户定义的设置。想要看这个“有效的 (effective)”POM,或者说Maven真正运行根据的POM,在simple项目的基础目录下跑下面的命令，

mvn help:effective-pom

一旦你运行了此命令,你应该能看到一个大得多的POM,它暴露了Maven的默认设置。这里我贴出一份有效的pom文件，也就是默认的那个pom文件。

ffective POMs, after inheritance, interpolation, and profiles are applied:<!-- ====================================================================== --><!--                                                                        --><!-- Generated by Maven Help Plugin on 2016-02-16T06:14:54                  --><!-- See: http://maven.apache.org/plugins/maven-help-plugin/                --><!--                                                                        --><!-- ====================================================================== --><!-- ====================================================================== --><!--                                                                        --><!-- Effective POM for project                                              --><!-- 'org.linkinpark.maven:linkinMaven:jar:0.0.1-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>org.linkinpark.maven</groupId>  <artifactId>linkinMaven</artifactId>  <version>0.0.1-SNAPSHOT</version>  <name>linkinMaven</name>  <url>http://maven.apache.org</url>  <properties>    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>  </properties>  <dependencies>    <dependency>      <groupId>junit</groupId>      <artifactId>junit</artifactId>      <version>4.12</version>      <scope>test</scope>    </dependency>    <dependency>      <groupId>org.hamcrest</groupId>      <artifactId>hamcrest-junit</artifactId>      <version>2.0.0.0</version>      <scope>test</scope>    </dependency>  </dependencies>  <repositories>    <repository>      <snapshots>        <enabled>false</enabled>      </snapshots>      <id>central</id>      <name>Central Repository</name>      <url>https://repo.maven.apache.org/maven2</url>    </repository>  </repositories>  <pluginRepositories>    <pluginRepository>      <releases>        <updatePolicy>never</updatePolicy>      </releases>      <snapshots>        <enabled>false</enabled>      </snapshots>      <id>central</id>      <name>Central Repository</name>      <url>https://repo.maven.apache.org/maven2</url>    </pluginRepository>  </pluginRepositories>  <build>    <sourceDirectory>/Users/LinkinPark/WorkSpace/linkinMaven/src/main/java</sourceDirectory>    <scriptSourceDirectory>/Users/LinkinPark/WorkSpace/linkinMaven/src/main/scripts</scriptSourceDirectory>    <testSourceDirectory>/Users/LinkinPark/WorkSpace/linkinMaven/src/test/java</testSourceDirectory>    <outputDirectory>/Users/LinkinPark/WorkSpace/linkinMaven/target/classes</outputDirectory>    <testOutputDirectory>/Users/LinkinPark/WorkSpace/linkinMaven/target/test-classes</testOutputDirectory>    <resources>      <resource>        <directory>/Users/LinkinPark/WorkSpace/linkinMaven/src/main/resources</directory>      </resource>    </resources>    <testResources>      <testResource>        <directory>/Users/LinkinPark/WorkSpace/linkinMaven/src/test/resources</directory>      </testResource>    </testResources>    <directory>/Users/LinkinPark/WorkSpace/linkinMaven/target</directory>    <finalName>linkinMaven-0.0.1-SNAPSHOT</finalName>    <pluginManagement>      <plugins>        <plugin>          <artifactId>maven-antrun-plugin</artifactId>          <version>1.3</version>        </plugin>        <plugin>          <artifactId>maven-assembly-plugin</artifactId>          <version>2.2-beta-5</version>        </plugin>        <plugin>          <artifactId>maven-dependency-plugin</artifactId>          <version>2.8</version>        </plugin>        <plugin>          <artifactId>maven-release-plugin</artifactId>          <version>2.3.2</version>        </plugin>      </plugins>    </pluginManagement>    <plugins>      <plugin>        <artifactId>maven-clean-plugin</artifactId>        <version>2.5</version>        <executions>          <execution>            <id>default-clean</id>            <phase>clean</phase>            <goals>              <goal>clean</goal>            </goals>          </execution>        </executions>      </plugin>      <plugin>        <artifactId>maven-resources-plugin</artifactId>        <version>2.6</version>        <executions>          <execution>            <id>default-testResources</id>            <phase>process-test-resources</phase>            <goals>              <goal>testResources</goal>            </goals>          </execution>          <execution>            <id>default-resources</id>            <phase>process-resources</phase>            <goals>              <goal>resources</goal>            </goals>          </execution>        </executions>      </plugin>      <plugin>        <artifactId>maven-jar-plugin</artifactId>        <version>2.4</version>        <executions>          <execution>            <id>default-jar</id>            <phase>package</phase>            <goals>              <goal>jar</goal>            </goals>          </execution>        </executions>      </plugin>      <plugin>        <artifactId>maven-compiler-plugin</artifactId>        <version>3.1</version>        <executions>          <execution>            <id>default-compile</id>            <phase>compile</phase>            <goals>              <goal>compile</goal>            </goals>          </execution>          <execution>            <id>default-testCompile</id>            <phase>test-compile</phase>            <goals>              <goal>testCompile</goal>            </goals>          </execution>        </executions>      </plugin>      <plugin>        <artifactId>maven-surefire-plugin</artifactId>        <version>2.12.4</version>        <executions>          <execution>            <id>default-test</id>            <phase>test</phase>            <goals>              <goal>test</goal>            </goals>          </execution>        </executions>      </plugin>      <plugin>        <artifactId>maven-install-plugin</artifactId>        <version>2.4</version>        <executions>          <execution>            <id>default-install</id>            <phase>install</phase>            <goals>              <goal>install</goal>            </goals>          </execution>        </executions>      </plugin>      <plugin>        <artifactId>maven-deploy-plugin</artifactId>        <version>2.7</version>        <executions>          <execution>            <id>default-deploy</id>            <phase>deploy</phase>            <goals>              <goal>deploy</goal>            </goals>          </execution>        </executions>      </plugin>      <plugin>        <artifactId>maven-site-plugin</artifactId>        <version>3.3</version>        <executions>          <execution>            <id>default-site</id>            <phase>site</phase>            <goals>              <goal>site</goal>            </goals>            <configuration>              <outputDirectory>/Users/LinkinPark/WorkSpace/linkinMaven/target/site</outputDirectory>              <reportPlugins>                <reportPlugin>                  <groupId>org.apache.maven.plugins</groupId>                  <artifactId>maven-project-info-reports-plugin</artifactId>                </reportPlugin>              </reportPlugins>            </configuration>          </execution>          <execution>            <id>default-deploy</id>            <phase>site-deploy</phase>            <goals>              <goal>deploy</goal>            </goals>            <configuration>              <outputDirectory>/Users/LinkinPark/WorkSpace/linkinMaven/target/site</outputDirectory>              <reportPlugins>                <reportPlugin>                  <groupId>org.apache.maven.plugins</groupId>                  <artifactId>maven-project-info-reports-plugin</artifactId>                </reportPlugin>              </reportPlugins>            </configuration>          </execution>        </executions>        <configuration>          <outputDirectory>/Users/LinkinPark/WorkSpace/linkinMaven/target/site</outputDirectory>          <reportPlugins>            <reportPlugin>              <groupId>org.apache.maven.plugins</groupId>              <artifactId>maven-project-info-reports-plugin</artifactId>            </reportPlugin>          </reportPlugins>        </configuration>      </plugin>    </plugins>  </build>  <reporting>    <outputDirectory>/Users/LinkinPark/WorkSpace/linkinMaven/target/site</outputDirectory>  </reporting></project>

关于详细的POM文件，我后面会专门整理到的。

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