[Maven一]Maven概览

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Maven

什么是Maven

Maven这个单词意为知识的积累，最早在Jakata Turbine项目中它开始被用来试图简化构建过程，Maven是一种很方便的发布项目信息的方式，以及一种在多个项目中共享JAR的方式。
Maven是项目管理工具，它为项目构建、测试、打包、部署定义了一个标准的生命周期。。
Maven基于一个通用的软件对象模型（Project Object Model），也就是POM。
Maven项目属于Apache软件基金会的一个顶级项目http://maven.apache.org/。Apache的很多项目都是基于Maven来管理的。同时，越来越多的项目和产品使用Maven作为他们项目管理的基础。它变得易于在项目和构建系统建立关系，并且在这个关系之上导航和做报告。
Maven的规范和中央仓库为项目定义了一种全新的命名系统。使用Maven可以很容易的加入其他的依赖项，并发布你自己的组件。

Maven体系结构

图片来源：http://zc985552943.iteye.com/blog/2090260

Maven安装

下载Maven

最新版本3.2.2，http://maven.apache.org/download.cgi
解压
sudo vim /etc/profile

在最后添加系统变量M2_HOME

export M2_HOME=/home/tom/devsoftware/apache-maven-3.2.2
export PATH=$PATH:$M2_HOME/bin

source /etc/profile
验证安装成功

在用户根目录下输入mvn v，察看Maven是否安装成功

Apache Maven 3.2.2 (45f7c06d68e745d05611f7fd14efb6594181933e; 2014-06-17T21:51:42+08:00)
Maven home: /home/tom/devsoftware/apache-maven-3.2.2
Java version: 1.7.0_55, vendor: Oracle Corporation
Java home: /software/devsoftware/jdk1.7.0_55/jre
Default locale: zh_CN, platform encoding: UTF-8
OS name: "linux", version: "3.2.0-39-generic", arch: "amd64", family: "unix"

Maven版本的Hello World

在~/learnmaven/maven-ch01中新建空的pom.xml,运行mvn compile,会报错，提示pom.xml文件必需的内容缺失

在pom.xml添加必需的xml内容，

<?xml version="1.0" encoding="UTF-8"?>
<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">

    <!--mandatory element in the project-->
    <modelVersion>4.0.0</modelVersion>

    <!--mandatory 3 elements in the project，这是确定唯一Maven模块的三元组-->
    <groupId>LearnMaven</groupId>
    <artifactId>LearnMaven</artifactId>
    <version>1.0</version>

</project>

project的四个子元素，modelVersion，groupId，artifactId和version是四个必需的元素，运行mvn compile之后，得到的结果是

[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building LearnMaven 1.0
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ LearnMaven ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /home/tom/development/learnmaven/maven-ch01/src/main/resources
[INFO] 
[INFO] --- maven-compiler-plugin:2.5.1:compile (default-compile) @ LearnMaven ---
[INFO] No sources to compile
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.707 s
[INFO] Finished at: 2014-08-02T00:22:44+08:00
[INFO] Final Memory: 6M/106M
[INFO] ------------------------------------------------------------------------

在~/learnmaven/maven-ch01目录下创建Maven的标准Maven模块的目录结构

mkdir -p src/main/java

mkdir -p src/main/resources

mkdir -p src/test/java

4. 在 src/main/java目录执行命令mkdir -p com/tom

在 src/test/java目录执行命令mkdir -p com/tom

5. 在com/tom目录下创建一个Java类

package com.tom;
public class HelloMaven {
    public String hi(String name){
        return "Hi " + name + ",welcome to the Maven world";
    }
}

6.回到~/learnmaven/maven-ch01目录执行命令mvn compile,得到如下输出，说明HelloMaven已经编译成功，编译的目标路径是target/classes

[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building LearnMaven 1.0
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ LearnMaven ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] Copying 0 resource
[INFO] 
[INFO] --- maven-compiler-plugin:2.5.1:compile (default-compile) @ LearnMaven ---
[WARNING] File encoding has not been set, using platform encoding UTF-8, i.e. build is platform dependent!
[INFO] Compiling 1 source file to /home/tom/development/learnmaven/maven-ch01/target/classes
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.928 s
[INFO] Finished at: 2014-08-02T00:40:23+08:00
[INFO] Final Memory: 9M/107M
[INFO] -----------------------------------------------------------------------

察看target/classes目录，可以发现com/tom/HelloMaven.classes

7. 在src/test/java/com/tom编写HelloMaven的单元测试类

package com.tom;

import org.junit.Assert;
import org.junit.Test;

public class HelloMavenTest {

    @Test
    public void testHi() {
        String name = "tom";
        HelloMaven hm = new HelloMaven();
        Assert.assertEquals("Hi tom,welcome to the Maven world",hm.hi(name));
    }

}

8.为pom.xml添加junit4依赖，pom.xml为

<?xml version="1.0" encoding="UTF-8"?>
<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">

    <!--mandatory element in the project-->
    <modelVersion>4.0.0</modelVersion>

    <!--mandatory 3 elements in the project-->
    <groupId>LearnMaven</groupId>
    <artifactId>LearnMaven-ch01</artifactId>
    <version>1.0</version>

    <dependencies>
        <!--JUnit 4.11-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
        </dependency>
    </dependencies>

</project>

9.在回到~/learnmaven/maven-ch01目录执行命令mvn compile test，看到测试代码编译并且执行，

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running com.tom.HelloMavenTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.094 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 9.853 s
[INFO] Finished at: 2014-08-02T01:25:38+08:00
[INFO] Final Memory: 17M/170M
[INFO] ------------------------------------------------------------------------

结果显示：测试用例成功执行，并且在target下创建了surefire-reports目录，在这个目录中创建了关于测试结果的信息文件

Maven模块依赖

1.在Maven Hello World的基础上，重新创建一个Maven模块，LearnMavenCh02,创建Maven的标准目录结构src/main/java和src/test/java等

2.在src/main/java/com/tom目录下，新建一个Java类，这个类依赖于Maven HelloWorld的HelloMaven，代码：

package com.tom;
public class HelloMavenCh02 {
    public String hi(String name){
        return new HelloMaven().hi(name);
    }
}

因为LearnMaven02模块依赖于LearnMaven01模块，因此，我们需要将对LearnMaven01模块的依赖加入到LearnMaven02模块中，pom文件的内容如下

<?xml version="1.0" encoding="UTF-8"?>
<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">

    <!--mandatory element in the project-->
    <modelVersion>4.0.0</modelVersion>

    <!--mandatory 3 elements in the project-->
    <groupId>LearnMaven</groupId>
    <artifactId>LearnMaven-ch02</artifactId>
    <version>1.0</version>

    <dependencies>
        <!--JUnit 4.11-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
        </dependency>
        <dependency>
            <groupId>LearnMaven</groupId>
            <artifactId>LearnMaven-ch01</artifactId>
            <version>1.0</version>
        </dependency>
    </dependencies>


</project

3.执行命令mvn compile,报错，报错信息是

[ERROR] Failed to execute goal on project LearnMaven-ch02: Could not resolve dependencies for project LearnMaven:LearnMaven-ch02:jar:1.0: Failure to find LearnMaven:LearnMaven-ch01:jar:1.0 in http://repo.maven.apache.org/maven2 was cached in the local repository, resolution will not be reattempted until the update interval of central has elapsed or updates are forced -> [Help 1]

意思是在中央仓库找不到LearnMaven-ch01,原因是我们还没有将LearnMaven-ch01放到本地仓库中

4.对LearnMaven01模块执行mvn install命令，将LearnMaven01模块添加到本地仓库.在LearnMaven01模块的~/development/learnmaven/maven-ch01目录执行mvn install，可以看到LearnMaven-ch01模块已经添加到本地仓库中，本地仓库路径~/.m2/repository/LearnMaven/LearnMaven-ch01/1.0/LearnMaven-ch01-1.0.jar

5.回到~/development/learnmaven/maven-ch02目录执行mvn compile发现LearnMaven-ch02模块编译成功

仓库

1.在pom.xml中定义的dependency，当查找这些依赖的jar包时候，首先从本地仓库中，然后再到全球的中央Maven库中下载，比如http://mvnrepository.com/中查找下载

2. 本地仓库~/.m2/repository

执行mvn install是将Maven模块打包后发布到本地仓库中，本地仓库的路径是在M2_HOME/conf/settings.xml中指定，

  <!-- localRepository
   | The path to the local repository maven will use to store artifacts.
   |
   | Default: ${user.home}/.m2/repository
  <localRepository>/path/to/local/repo</localRepository>
  -->

3. 中央仓库，默认的配置是在$M2_HOME/lib/maven-settings-builder-3.2.2.jar包的pom-4.0.0.xml中，

 <repositories>
    <repository>
      <id>central</id>
      <name>Central Repository</name>
      <url>http://repo.maven.apache.org/maven2</url>
      <layout>default</layout>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
    </repository>
  </repositories>

  <pluginRepositories>
    <pluginRepository>
      <id>central</id>
      <name>Central Repository</name>
      <url>http://repo.maven.apache.org/maven2</url>
      <layout>default</layout>
      <snapshots>
        <enabled>false</enabled>
      </snapshots>
      <releases>
        <updatePolicy>never</updatePolicy>
      </releases>
    </pluginRepository>
  </pluginRepositories>