第一个简单的maven项目

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
{

@Test
public 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.HelloTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.052 sec

Results :

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。