maven入门学习及环境搭建
本文将简单介绍maven及使用命令，重点介绍如何搭建maven开发环境，最后给出一个利用maven创建项目的例子。
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一 maven是什么
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简单的说，maven是项目构建和依赖管理的工具。
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利用maven可以脱离IDE创建、编译，打包、发布项目。类似产品如ant。
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二 快速了解
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Based on the concept of a project object model (POM), Maven can manage a project's build, reporting and documentation from a central piece of information.
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At first glance Maven can appear to be many things, but in a nutshell Maven is an attempt?to apply patterns to a project's build infrastructure in order to promote comprehension and productivity by providing a clear path in the use of best practices. Maven is essentially a project management and comprehension tool and as such provides a way to help with managing:
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链接：http://maven.apache.org/users/index.html
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三 下载安装
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以下安装测试是在window7，Eclipse Java EE IDE for Web Developers?Version: Helios Service Release 2（3.6）上进行的。
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A 在系统中安装maven工具（环境）
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安装maven之前确保已经配置好了JDK环境（jre不行，必须是jdk环境）。
下载地址：http://labs.mop.com/apache-mirror/maven/binaries/apache-maven-3.0.4-bin.zip
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window上安装配置如下，其他操作系统详见http://maven.apache.org/download.html#Installation
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1.下载后解压到任意位置，如：D:\dev\apache-maven-3.0.4
2.配置环境变量，在用户变量中增加：
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key：M2_HOMEvalue如： D:\dev\apache-maven-3.0.4
key：M2value：%M2_HOME%\bin
key：MAVEN_OPTSvalue如： -Xms256m -Xmx512m（此属性值可选）
key：Pathvalue：%M2%（添加或更新）
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然后检查JAVA_HOME属性是否配置的为jdk的环境，而且Path中是否配置了?%JAVA_HOME%\bin 值，配置完毕后，在控制台中运行如下命令：
?mvn --version
如果打印版本信息则说明安装成功。
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maven使用本地库来存放项目所需的jar包，安装完毕maven后maven会将${user.home}/.m2/repository/位置作为默认本地库位置。安装完后最好自己重新配置本地库位置，配置方法如下：
在${user.home}/.m2/目录下增加settings.xml文件，内如如下：
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<?xml version="1.0" encoding="UTF-8"?>
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安装完插件后重启eclipse可能会提示：?Eclipse is running in a JRE, but a JDK is required
Some Maven plugins may not work when importing projects or updating source folders.错误。
因为maven需要使用JDK而不是jre，所以需要修改两个位置对jdk的引用：
1. 修改installed JREs，把默认jre改为JDK路径
2. 修改eclipse运行环境应用的jre：在eclipse.ini文件中增加如下参数
-vm
C:\Program Files (x86)\Java\jdk1.6.0_14\bin\javaw.exe
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然后重启eclipse应该就不再提示jre的问题了。
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安装完m2eclipse插件最好配置一下：
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四 常用
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其实没有eclipse插件我们照样也可以使用maven来创建和管理项目，但只是不太那么方便，有了插件与IDE集成，就免去在控制台中输入繁琐命令的麻烦。
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快速使用示例：
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下面介绍在控制台命令行中使用maven来创建项目的示例。
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1.创建工程
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在windows命令行中，首先进入某个文件夹下（这个文件即作为工作空间了），如D:\pro，然后输入下面的命令在这个位置创建一个名称为my-app的项目。
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上面的步骤创建项目结构如下：
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my-app|-- pom.xml`-- src |-- main | `-- java | `-- com | `-- mycompany | `-- app | `-- App.java `-- test `-- java `-- com `-- mycompany `-- app `-- AppTest.java?
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2. 编写java文件
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进入项目目录，D:\pro\my-app\src\main\java\com\mycompany\app下有个示例java文件App.java
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如果自己编写java文件就放在\src\main\java下；
如果是资源文件如属性配置文件放在\src\main\resources下，编译或打包时这个位置等同于\src\main\java；
测试文件存放位置：\src\test
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3. 编译项目
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在命令行中输入如下命令：
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4. 测试项目
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在命令行中输入如下命令
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5. 项目打包
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在命令行中输入如下命令即可将项目打包，maven会根据不同的项目类型将项目打为不同的包，如jar，war等。打包前会先对项目进行一次编译、测试，然后才打包。
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6. 运行项目或将项目包发布到库中
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打包后的项目可以来运行或者安装到本地库中以便其他项目引用。
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运行此示例项目：
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将项目包安装到本地库中，同样执行安装过程也会先执行编译、测试、打包、最后才将包复制到本地库中。
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至此，一个简单maven使用入门教程学习完毕。在eclipse中使用maven开发项目的方法估计可以类比命令行中的使用过程。
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至于更加详细具体的如何使用maven来工作，自己可以从网上去查阅资料，学习别人的最佳实践经验，也可以自己取探索，以后我再慢慢补充。
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下面引用maven官方对maven常用命令的介绍
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Running Maven ToolsMaven Phases
Although hardly a comprehensive list, these are the most common?default?lifecycle phases executed.
There are two other Maven lifecycles of note beyond the?default?list above. They are
Phases are actually mapped to underlying goals. The specific goals executed per phase is dependant upon the packaging type of the project. For example,?package?executes?jar:jar?if the project type is a JAR, and?war:war?is the project type is - you guessed it - a WAR.
An interesting thing to note is that phases and goals may be executed in sequence.
mvn clean dependency:copy-dependencies package
This command will clean the project, copy dependencies, and package the project (executing all phases up to?package, of course).
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一个简单的POM示例：
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mvn compile?
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How do I compile my test sources and run my unit tests?
Now you're successfully compiling your application's sources and now you've got some unit tests that you want to compile and execute (because every programmer always writes and executes their unit tests *nudge nudge wink wink*).
Execute the following command:
mvn test?
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How do I create a JAR and install it in my local repository?
Making a JAR file is straight forward enough and can be accomplished by executing the following command:
mvn packageIf you take a look at the POM for your project you will notice the?packaging?element is set to?jar. This is how Maven knows to produce a JAR file from the above command (we'll talk more about this later). You can now take a look in the?${basedir}/target?directory and you will see the generated JAR file.
Now you'll want to install the artifact you've generated (the JAR file) in your local repository (~/.m2/repository?is the default location). For more information on repositories you can refer to our?Introduction to Repositories?but let's move on to installing our artifact! To do so execute the following command:
mvn install?
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There are plenty of other standalone goals that can be executed as well, for example:
mvn cleanThis will remove the?target?directory with all the build data before starting so that it is fresh.
Perhaps you'd like to generate an IntelliJ IDEA descriptor for the project?
mvn idea:ideaThis can be run over the top of a previous IDEA project - it will update the settings rather than starting fresh.
If you are using Eclipse IDE, just call:
mvn eclipse:eclipse?
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How do I add resources to my JAR?
Another common use case that can be satisfied which requires no changes to the POM that we have above is packaging resources in the JAR file. For this common task, Maven again relies on the?Standard Directory Layout, which means by using standard Maven conventions you can package resources within JARs simply by placing those resources in a standard directory structure.
You see below in our example we have added the directory?${basedir}/src/main/resources?into which we place any resources we wish to package in our JAR. The simple rule employed by Maven is this: any directories or files placed within the?${basedir}/src/main/resources?directory are packaged in your JAR with the exact same structure starting at the base of the JAR.
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How do I build other types of projects?
Note that the lifecycle applies to any project type. For example, back in the base directory we can create a simple web application:
mvn archetype:generate \ -DarchetypeGroupId=org.apache.maven.archetypes \ -DarchetypeArtifactId=maven-archetype-webapp \ -DgroupId=com.mycompany.app \ -DartifactId=my-webappNote that these must all be on a single line. This will create a directory called?my-webapp?containing the following project descriptor:
<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>com.mycompany.app</groupId> <artifactId>my-webapp</artifactId> <version>1.0-SNAPSHOT</version> <packaging>war</packaging> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>3.8.1</version> <scope>test</scope> </dependency> </dependencies> <build> <finalName>my-webapp</finalName> </build></project>?
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