Maven：使用入门

一、编写POM 
Maven项目的核心是pom.xml； 
POM(Project Object Model，项目对象模型）定义了项目的基本信息，用于描述项目如何构建，声明项目依赖； 
POM文件： 

<?xml version="1.0" encoding="UTF-8"?>                                    //XML头，指定xml文档的版本和编码方式 
<project xmlns="http://maven.apache.org/POM/4.0.0"                        //project根元素，命名空间，避免命名重复 
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0"> 
  <modleVersion>4.0.0</modleVersion>                                      //modleVersion 当前POM模型版本 
  <groupId>com.juvenxu.mvnbook</groupId>                                  //groupId 项目属于哪个组 
  <artifactId>hello-world</artifactId>                                    //artifactId 项目在组中的唯一ID 
  <version>1.0-SNAPSHOT</version>                                         //version 项目当前版本（SNAPSHOT正在开发、不稳定版本） 
  <name>Maven Hello World Project</name>                                  //name 一个对用户更友好的项目名称 
</project> 

没有任何Java代码，就能够定义Maven项目的POM，让项目对象模型最大程度地和实际代码相互独立-解耦； 
二、编写主代码 
项目主代码和测试代码不同，项目主代码会被打包到最终的构建中（如jar），而测试代码只在运行测试时用到； 
默认情况下，Maven假设项目主代码位于src/main/java目录中，然后在该目录下创建包名和源文件； 
HelloWorld.java： 

public class HelloWorld { 
  public String sayHello() { 
    return "Hello Maven"; 
  }  
  public static void main(String[] args) { 
    System.out.print(new HelloWorld().sayHello()); 
  } 
} 

在项目根目录下，运行命令mvn clean compile 

C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world>mvn clean compile 
[INFO] Scanning for projects... 
[INFO] 
[INFO] ------------------------------------------------------------------------ 
[INFO] Building Maven Hello World Project 1.0-SNAPSHOT 
[INFO] ------------------------------------------------------------------------ 
[INFO] 
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ hello-world ---               //执行clean:clean任务，删除target/目录 
[INFO] Deleting C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world\target 
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ hello-world ---   //执行resources:resources任务，未定义项目资源 
[WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent! 
[INFO] skip non existing resourceDirectory C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world\src\main\resources 
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ hello-world ---        //执行compile:compile任务，编译项目主代码至target/classes目录 
[INFO] Changes detected - recompiling the module! 
[WARNING] File encoding has not been set, using platform encoding GBK, i.e. build is platform dependent! 
[INFO] Compiling 1 source file to C:\Users\chengxiang.peng.QUNARSERVERS\MavenSou 
rces\hello-world\target\classes 
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS 
[INFO] ------------------------------------------------------------------------ 
[INFO] Total time: 1.466 s 
[INFO] Finished at: 2015-05-01T11:54:18+08:00 
[INFO] Final Memory: 12M/219M 
[INFO] ------------------------------------------------------------------------

三、编写测试代码 
Maven项目中默认的测试代码目录是src/test/java； 
HelloWorldTest.java:

public class HelloWorldTest{ 
    @Test 
    public void testSayHello(){ 
        HelloWorld helloWorld = new HelloWorld(); 
        String result = helloWorld.sayHello() 
        assertEquals( "Hello Maven", result ); 
    } 
}

POM文件如下： 

<?xml version="1.0" encoding="UTF-8"?> 
<project xmlns="http://maven.apache.org/POM/4.0.0" 
    … …  
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0"> 
  <modelVersion>4.0.0</modelVersion> 
    … …  
  <name>Maven Hello World Project</name> 
  <dependencies>                                     //dependencied元素，可以包含多个dependency元素以声明项目的依赖 
    <dependency> 
      <groupId>junit</groupId>                       //添加junit依赖，自动访问中央仓库下载需要的文件 
      <artifactId>junit</artifactId> 
      <version>4.7</version> 
      <scope>test</scope>                            //scop依赖范围，标识该依赖只对测试有效（如果不声明依赖范围，那么默认值就是compile，标识该依
      </dependency>                                  //赖对主代码和测试代码都有效） 
  </dependencies> 
</project> 

执行mvn clean test 

C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world>mvn clean test 
[INFO] Scanning for projects... 
[INFO] 
[INFO] ------------------------------------------------------------------------ 
[INFO] Building Maven Hello World Project 1.0-SNAPSHOT 
[INFO] ------------------------------------------------------------------------ 
[INFO] 
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ hello-world --- 
[INFO] Deleting C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world\target 
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ hello-world --- 
[WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent! 
[INFO] skip non existing resourceDirectory C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world\src\main\resources 
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ hello-world --- 
[INFO] Changes detected - recompiling the module! 
[WARNING] File encoding has not been set, using platform encoding GBK, i.e. build is platform dependent! 
[INFO] Compiling 1 source file to C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world\target\classes 
[INFO] 
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ hello-world --- 
[WARNING] Using platform encoding (GBK actually) to copy filtered resources, i.e. build is platform dependent! 
[INFO] skip non existing resourceDirectory C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world\src\test\resources 
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ hello-world ---       //compiler:testCompile任务，编译测试代码 
[INFO] Changes detected - recompiling the module! 
[WARNING] File encoding has not been set, using platform encoding GBK, i.e. build is platform dependent! 
[INFO] Compiling 1 source file to C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world\target\test-classes 
[INFO] 
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ hello-world ---                  //surefire:test任务，负责执行测试的插件 
[INFO] Surefire report directory: C:\Users\chengxiang.peng.QUNARSERVERS\MavenSou 
rces\hello-world\target\surefire-reports 
-------------------------------------------------------                                        //输出测试报告 
 T E S T S 
------------------------------------------------------- 
Running com.juvenxu.mvnbook.helloworld.HelloWorldTest 
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.063 sec 
Results : 
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0 
[INFO] ------------------------------------------------------------------------ 
[INFO] BUILD SUCCESS 
[INFO] ------------------------------------------------------------------------ 
[INFO] Total time: 2.605 s 
[INFO] Finished at: 2015-05-01T16:23:59+08:00 
[INFO] Final Memory: 13M/154M 
[INFO] ------------------------------------------------------------------------ 

四、打包和运行 
将项目进行编译、测试之后，下一个重要的步骤就是打包（package），执行命令mvn clean package进行打包； 

C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world>mvn clean package 
[INFO] Scanning for projects... 
….. …… 
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ hello-world ---                //jar:jar任务，负责打包               
[INFO] Building jar: C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world\target\hello-world-1.0-SNAPSHOT.jar 
…… …..  

如何才能让其他的项目直接饮用这个jar呢，执行mvn clean install命令 

C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world>mvn clean install 
[INFO] Scanning for projects... 
…… …… 
[INFO] --- maven-install-plugin:2.4:install (default-install) @ hello-world ---  //执行安装任务install:install，将项目输出的jar包安装到Maven本地仓库中 
[INFO] Installing C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world\target\hello-world-1.0-SNAPSHOT.jar to C:\Users\chengxiang.peng.QUNARSERVERS\.m2\repository\com\juvenxu\mvnbook\hello-world\1.0-SNAPSHOT\hello-world-1.0-SNAPSHOT.jar 
[INFO] Installing C:\Users\chengxiang.peng.QUNARSERVERS\MavenSources\hello-world\pom.xml to C:\Users\chengxiang.peng.QUNARSERVERS\.m2\repository\com\juvenxu\mvnbook\hello-world\1.0-SNAPSHOT\hello-world-1.0-SNAPSHOT.pom 
…… ……  

默认打包生成的jar是不能够直接运行的，因为带有main方法的类信息不会添加到manifext中（打开jar文件中的META_INF?MANIFEAT.MF文件，将无法看到Main-Class一行）； 
为了生成可执行的jar文件，需要借助maven-shade-plugin，配置改插件如下： 

   <plugins> 
    <plugin> 
      <groupId>org.apache.maven.plugins</groupId> 
      <artifactId>maven-shade-plugin</artifactId> 
      <version>1.2.1</version> 
      <executions> 
        <execution> 
          <phase>package</phase> 
          <goals> 
            <goal>shade</goal> 
          </goals> 
          <configuration> 
            <transformers> 
              <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer"> 
                <mainClass>com.juvenxu.mvnbook.helloworld.HelloWorld</mainClass>        //配置mainClass 
              </transformer> 
            </transformers> 
          </configuration> 
        </execution> 
      </executions> 
    </plugin>
    </plugins> 

构建完成之后打开target/目录，可以看到hello-world-1.0-SNAPHOST.jar和original-hello-world-SNAPHOST.jar，前者带有Main-Class信息可以运行jar，后者是原有的jar； 

打开hello-world-1.0-SNAPHOST.jar的META_INF/MANIFEST.MF文件如下： 

Manifest-Version: 1.0 
Build-Jdk: 1.7.0_71 
Built-By: chengxiang.peng 
Created-By: Apache Maven 3.3.1 
Main-Class: com.juvenxu.mvnbook.helloworld.HelloWorld 
Archiver-Version: Plexus Archiver 

在项目跟目录下执行java -jar target\hello-world-1.0-SNAPSHOT.jar 

五、使用Archetype生成项目骨架 
前面Hello World项目有一些Maven约定： 
    根目录放置pom.xml； 
    在src/main/java目录中放置项目的主代码； 
    在src/test/java中放置项目的测试代码； 
Maven提供了Archetype可以帮我们快速勾勒出项目骨架，执行mvn archetype:generate，根据提示输入相关信息生成Maven基本结构项目；