Terry.Li-彬

用 Maven 做項目管理在 Java世界中我們很多的開發人員選擇用 Ant來構建項目，一個 build.xml能夠完成編譯、測試、打包、部署等很多任務，但我們也碰到了很多的問題，如 jar文件管理混亂，各個項目結構和 build.xml相差很大等等。而 Maven的出現，給項目提供了更多的支持。



1        簡介 Maven 作為 Apache 的一個開源項目，旨在給項目管理提供更多的支持，主頁地址為 http://maven.apache.org 。它最早的意圖只是為了給 apache 組織的幾個項目提供統一的開發、測試、打包和部署，能讓開發者在多個項目中方便的切換。很多偉大的事業，出發點都很簡單， ebay 就是很好的例證。而 maven 的成功又一次驗證了這一點，越來越多的項目開始使用 maven 。
基本原理
Maven 的基本原理很簡單，采用遠程倉庫和本地倉庫以及一個類似 build.xml 的 pom.xml ，將 pom.xml 中定義的 jar 文件從遠程倉庫下載到本地倉庫，各個應用使用同一個本地倉庫的 jar ，同一個版本的 jar 只需下載一次，而且避免每個應用都去拷貝 jar 。如圖 1 。同時它采用了現在流行的插件體系架構，只保留最小的核心，其余功能都通過插件的形式提供，所以 maven 下載很小（ 1.1M ），在執行 maven 任務時，才會自動下載需要的插件。
這個基本原理與 Pear ――ＰＨＰ擴展與應用庫（ the PHP Extension and Application Repository ）的原理非常相似，都有一個官方的倉庫，都是微內核，通過網絡將需要的文件下載到本地，通過官方倉庫將相應的類庫進行統一管理。 Pear 已經成為 PHP 開發事實上的標準，而 Maven 在 Java 世界的地位也逐漸加強，成為標準指日可待。
另外由于插件的易開發性，現在有了非常多的可供選擇的插件，如與 eclipse 結合的插件，與 test 相關的插件，后面我們結合 maven 在項目中的使用進行詳細介紹。

2        項目管理 Maven 官方把 maven 定義為一個項目管理工具，我們不妨看看 maven 能給我們的項目提供哪些好的支持。
2.1       項目標準化 Maven 一個重要特性是定義了項目的標準模板，官方說法是最佳實踐。可以通過命令： mvn archetype:create -DgroupId=com.mycompany.app -DartifactId=my-app 創建一個單一的 maven 項目。創建好的項目，具有了特定的項目結構。這個項目結構是參考業界的最佳實踐而成，為后面使用統一的 maven 命令打下了基礎，如測試 mvn test 、打包 mvn package 等，無需寫一行腳本，就可以方便的實現眾多功能。 Maven 還提供其它一些類型模板，可以通過添加 -DarchetypeArtifactId= ｛ type ｝創建，如 -DarchetypeArtifactId=maven-archetype-site ，生成 site 類型的項目。
同時一些好的開源軟件使用了 maven ，也能作為很好的項目模板，如 Equinox （ Appfuse 的簡化版），它的 pom 定義了對 hiberante,spring… 的依賴，可以通過 ant new -Dapp.name=NAME 快速生成項目原型，然后對 pom 文件進行裁減，以符合自身項目的需要。
有了這個標準，項目間能方便的進行交流，你也很容易了解其它使用 maven 項目的結構。對于企業來說，引入 maven 就自然引入了規范，這可比費時費力的寫文檔，定規范有效的多了。
2.2       文檔和報告 使用 mvn site 可以快速生成項目站點， apache 很多開源項目站點都采用 maven 生成，會出現 built by maven 字樣的圖標。
而 maven 提供的針對如 junit ， checkstyle ， pmd 等的插件，能夠方便的進行測試和檢查并能直接生成報告。使用都很簡單，如 mvn surefire-report:report 就能自動進行 junit 測試，并生成 junit 報告， mvn pmd:pmd 生成 pmd 報告。具體使用可以在 http://maven.apache.org/plugins/index.html 找到。
2.3       類庫管理 Maven 一個很重要的特色就是類庫管理。通過在 pom.xml 中定義 jar 包版本和依賴，能夠方便的管理 jar 文件。以下是一個簡單的 jar 定義片斷：

<dependency>                                                                              <groupId>org.hibernate</groupId>       <artifactId>hibernate</artifactId>       <version>3.1</version>       <type>jar</type>       <scope>runtime</scope>   </dependency>

這個片斷告訴我們，依賴的 jar 包 groupId 為 org.hibernate ， artifactId 為 hibernate ，版本為 3.1 ， scope 為 runtime 。在實際項目中，會將 M2_REPO(maven 本地倉庫地址 )/ org/hibernate / hibernate /3.1/ hibernate -3.1.jar 放入 classpath 。
同時 maven 會通過 pom.xml 管理 jar 包間的依賴。比如上面的 hibernate-3.1.jar 同級目錄肯定會有一個 hibernate -3.1.pom ，在這個 pom 文件中指定了這個 jar 對其它一些 jar 的依賴。而這個 pom 文件是遠程倉庫提供，無需進行修改，執行 maven 相關命令就會自動根據相關依賴去下載 jar 包。這樣只需定義對 hibernate 的依賴而無需關心相關 jar ，在構建項目上方便了很多。
因為 pom 文件對 jar 的管理，也產生了一個很吸引人的特性：項目文件很小。以往一個 web 項目中， jar 文件都要放入 WEB-INF/lib 下，并放入 cvs(svn) 中，很容易就達到幾十 M 。而通過 maven ，只需一個 pom.xml ，在執行 mvn eclipse:eclipse 時再去遠程倉庫下載，項目文件一般只需幾百 K 。
2.4       發布管理 使用 maven 可以方便的進行項目發表管理。在項目開發到一定階段，可以使用 mvn package 打包，它會自動先運行 mvn test ，跑所有的 testcase ，只有全部通過才能正確打包。生成的 war 包（如果項目的 packaging 為 war ）在 target 目錄下。這個 war 包與使用 ant 腳本生成一樣，但無需一行腳本，這也是 maven 對比 ant 的優勢之一。使用 mvn install 將編譯和打包好的文件發布到 distributionManager 指定的遠程 repository 。使用 mvn deploy 可以自動管理項目版本。
  
3         使用 maven Maven 使用簡單，插件豐富且經過大量項目考驗，在項目中引入的風險很小。筆者在項目中使用 maven ，新進員工在半小時內就能成功使用 maven 構建項目，并很快掌握幾個常用的命令。 Maven 也不需要什么特殊的設施。如果項目全部使用開源軟件，并且不需要 maven 管理項目版本，只需要一個 SCM 環境（ CVS 或 SVN ），共享開發源碼就可以。把 pom.xml 中的 repository 設為官方地址就行，配置如下：

<repository>       <id>central</id>       <url>http://www.ibiblio.org/maven2</url> </repository>

這個官方 remote repository 上有非常多的開源軟件，應該能滿足大部分項目的需要。如果有項目需要而它上面暫時還沒有的軟件，或者希望使用公司內部的軟件，那么就需要自己配置一個 repository 了。
3.1       自建私服 傳奇私服大家應該都聽過，一個網吧自己搞個私服，一伙人免費在上面砍殺。官方因此少賺了很多錢，因此總想打擊。而 maven 官方卻對自建私服很是支持，我們總算可以正正當當搞把私服了（ Springside 的老大江南白衣就是創建私服的好手）。我們就來介紹下自建私服的最快方法。
首先需要一個 http server ，找臺服務器裝上 apache 就行。放一個空的 maven 目錄到 htdocs 下，假設服務器 ip 為 192.168.0.1 ，確認能用 http://192.168.0.1/maven 訪問到。然后在自己機器上裝好 maven2 ，初始化好項目，在 pom.xml 放入需要的 jar 定義，運行如 mvn eclipse:eclipse 就自動從官方下載 jar 到本地，如果不做配置，默認本地 repository 為 ${user.home}/.m2/ 。對于 windows xp 來說一般在 C:\Documents and Settings\ ％ username%\.m2 下，其中％ username ％為操作系統登錄用戶名。這時你可以看到 ${user.home}/.m2/ 下多了個 repository 目錄，里面有很多的項目相關 jar ，目錄按 groupId/ artifactId/version 排好。把 repository 目錄整個拷貝到 apache 服務器的 maven 目錄下，如果需要官方缺少的 jar 或公司內部 jar ，仿照這個目錄結構，做好 jar 放到 maven 目錄下。自建私服成功！
要使用私服，只需修改 pom.xml ，在 repository 配置后加上：

<repository>       <id>companyName</id>       <url>http:// ${ip}/maven</url> </repository>

這樣需要下載 jar 時，會先到本地 repository 查看，沒有下載過再到官方搜索，沒有找到再到后面的 repository 查找。
3.2       安裝配置 Maven 的安裝很簡單：
1.         從 apache 網站上下載 maven 安裝包，實際上就是個壓縮文件。將其解壓到你想要存放 maven 的目錄中。在這里假設你將 maven 解壓到 C:\Program Files\Apache Software Foundation\maven-2.0.4 中。
2.       將 C:\Program Files\Apache Software Foundation\maven-2.0.4\bin 設到你的系統環境變量%PATH%中。
3.       同時確保你已經將你的JDK安裝目錄設為java_home系統變量。
4.         打開個命令行窗口，運行 mvn –version 驗證是否安裝成功。
5.         如果使用 eclipse ，在運行 mvn eclipse:eclipse 生成 eclipse 項目文件后，需加入 M2_REPO 到 Classpath Variables 中，指向 本地 repository ，例如： C:/Documents and Settings/Owner/.m2/repository 。
3.3       基本使用流程 在項目進程中，不必做什么配置，在 pom.xml 同級目錄， cmd 使用簡單的 maven 命令，就可以完成初始化 -> 開發 -> 測試 -> 發布 的全過程。 Maven 的基本使用流程如下圖：

其中在初次使用命令 mvn eclipse:eclipse 時會下載很多的插件和 jar ，可能需要較長的時間，建議泡杯咖啡，和同事吹吹牛。如果失敗，可能是網絡問題，可以重新運行 mvn eclipse:eclipse ，已下載好的插件和 jar 不會再下。運行 mvn test 和 mvn package 等命令，產出物都會放在 target 目錄下。如果在使用過程中有什么問題，也可以和我聯系， mail:pesome@gmail.com ，我們一起來嘗試解決。
  
總結：
Maven 作為新的項目管理工具，簡單易用，能對項目的各個階段提供大力支持，同時由于它易擴展的插件體系架構，出現了越來越多的插件，也使得其功能更加強大。短短一篇文章，實在很難把其特點一一盡述， maven 還有很多好用的功能和插件等待我們去使用和開發。而學習新技術的最好方式就是實踐，大家如果有興趣，盡快下載一個最新版，開始你的 maven 之旅吧！
  
作者簡介：張俊，網名 pesome ，上海交大軟件工程碩士， 2 年 JavaEE 開發經驗，資歷尚淺。去年下半年開始接觸 spring 等開源軟件，并產生了濃厚的興趣。今年 3 月開始做 www.openfans.net ，用一堆開源軟件搭建而成，希望為中國的開源事業做出一點貢獻。
  
參考文檔：
1.       http://maven.apache.org 官方網站文檔
2.       http://www-128.ibm.com/developerworks/cn/opensource/os-maven2/ Maven2 的新特性


Posted by kevinwu on December 15, 2006 09:22 PM | 全文 |MAVEN|del.icio.us|VIVI|365key|blogChina|Poco|SOHU|Hexun

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Maven入門--較復雜的實例

</encoding>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <configuration>
                    <archive>
                        <addMavenDescriptor>false</addMavenDescriptor>
                    </archive>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <configuration>
                    <archive>
                        <addMavenDescriptor>false</addMavenDescriptor>
                    </archive>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-javadoc-plugin</artifactId>
                <configuration>
                    <charset>UTF16</charset>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">

Maven入門--概念與實例

3 標準目錄布局
    Maven為工程中的源文件，資源文件，配置文件，生成的輸出和文檔都制定了一個標準的目錄結構。Maven鼓勵使用標準目錄布局，這樣就不需要進行額外 的配置，而且有助于各個不同工程之間的聯接。當然，Maven也允許定制個性的目錄布局，這就需要進行更多的配置。關于Maven的標準目錄布局，請見參考資源[6]中的附錄B.1。
4 Maven的優點
    [1]build邏輯可以被重用。在Ant中可能需要多次重復地寫相同的語句，但由于POM的繼承性，可以復用其它的POM文件中的語句。這樣既可以寫出清晰的build語句，又可以構造出層次關系良好的build工程。
    [2]不必關注build工作的實現細節。我們只需要使用一些build生命周期短語就可以達到我們的目標，而不必管Maven是如何做到這些的。如，只需要告訴Maven要安裝(install)，那么它自然就會驗證，編譯，打包，及安裝。
    [3]Maven會自動加載工程依賴的artifact所依賴的其它artifact(Transitive Dependency)，而不用顯示的將這些artifact全部寫到dependency中。
    [4]如果完全使用Maven的標準目錄布局，那么可以極大地減少配置細節。
5 實例
5.1 構想
    由于只是闡述Maven的基本使用方法，所以本文將要設計的實例，只是一個簡單的Maven demo。該實例包含兩個工程：普通應用程序工程(app)和Web應用工程(webapp)。app工程提供一個簡單的Java類；webapp工程只 包含一個Servlet，并將使用app中的Java類。
    該Demo的目標是能夠正確地將webapp制成war包，以供部署時使用。要能夠正確制作war，自然首先就必須要能夠正確的編譯源代碼，且要將App模塊制成jar包。本文創建的工程所在的目錄是D:\maven\demo。
5.2 App工程
    可以使用Maven的archetype插件來創建新工程，命令如下：
    D:\maven\demo>mvn archetype:create -DgroupId=ce.demo.mvn -DartifactId=app
該工程的groupId是ce.demo.mvn，那么該工程的源文件將放在Java包ce.demo.mvn中。artifactId是app，那么該工程根目錄的名稱將為app。
    當第一次執行該命令時，Maven會從central倉庫中下載一些文件。這些文件包含插件archetype，以及它所依賴的其它包。該命令執行完畢后，在目錄D:\maven\demo下會出現如下目錄布局：
app
|-- pom.xml
`-- src
    |-- main
    |   `-- java
    |       `-- ce
    |           `-- demo
    |               `-- mvn
    |                   `-- App.java
    `-- test
        `-- java
            `-- ce
                `-- demo
                    `-- mvn
                        `-- AppTest.java
因本文暫時不涉及JUnit測試，故請將目錄app\src\test目錄刪除(不刪除也沒關系 ^_^)。然后再修改App.java文件，其完全內容如下：
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">package ce.demo.mvn;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">public class App screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">{
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    public String getStr(String str) screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">{
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        return str;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    }
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">}
其實，如果我們能夠清楚地知道Maven的標準目錄布局，就可以不使用archetype插件來創建工程原型；如果我們要定制個性的目錄布局，那么就更沒有必要使用archetype插件了。
5.3 WebApp工程
    我們仍然如創建app工程一樣使用archetype插件來創建webapp工程，命令如下：
    D:\maven\demo>mvn archetype:create -DgroupId=ce.demo.mvn -DartifactId=webapp -DarchetypeArtifactId=maven-archetype-webapp
    第一次運行此命令時，也會從central倉庫中下載一些與Web應用相關的artifact(如javax.servlet)。此命令與創建app的命 令的不同之處是，多設置了一個屬性archetypeArtifacttId，該屬性的值為maven-archetype-webapp。即告訴 Maven，將要創建的工程是一個Web應用工程。創建app工程時沒有使用該屬性值，是由于archetype默認創建的是應用程序工程。同樣的，執行 完該命令之后，會出現如下標準目錄布局：
webapp
|-- pom.xml
`-- src
    `-- main
        `-- webapp
            [size=+0]|-- index.jsp
            |-- WEB-INF
                `-- web.xml
    根據5.1節的構想，webapp工程將只包含一個Servlet，所以我們不需要index.jsp文件，請將其刪除。此時大家可以發現，目前的目錄布 局中并沒有放Servlet，即Java源文件的地方。根據參考資源[6]中的附錄B.1，以及app工程中Java源文件的布局，可以知道 Servlet（它仍然是一個Java類文件）仍然是放在webapp\src\main\java目錄中，請新建該目錄。此處的Servlet是一個簡單HelloServlet，其完整代碼如下：
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">package hello;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import java.io.IOException;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import java.io.PrintWriter;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import javax.servlet.ServletException;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import javax.servlet.http.HttpServlet;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import javax.servlet.http.HttpServletRequest;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import javax.servlet.http.HttpServletResponse;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import ce.demo.mvn.App;  // 引用app工程中的App類
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">public class HelloServlet extends HttpServlet screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">{
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    private static final long serialVersionUID = -3696470690560528247L;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    public void doGet(HttpServletRequest request, HttpServletResponse response)
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">            throws ServletException, IOException screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">{
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        App app = new App();
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        String str = app.getStr("CE Maven Demo");
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        PrintWriter out = response.getWriter();
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        out.print("<html><body>");
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        out.print("<h1>" + str);
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        out.print("</body></html>");
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    }
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">}
5.4 POM文件
    大家可以發現，在前面新建工程時，我們并沒有提到各個工程中的pom.xml文件。現在將要討論這個問題。我們先看看app工程中的POM文件，其完整內容如下：
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0"><project>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <modelVersion>4.0.0</modelVersion>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <groupId>ce.demo.mvn</groupId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <artifactId>app</artifactId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <packaging>jar</packaging>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <version>1.0</version>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <name>CE Maven Demo -- App</name>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0"></project>
    大家可以發現此我帖出來的內容與實際由archetype插件生成的POM文件的內容有些不同，但基本上是一致的。只是為了使文件中的語句更清晰，此處刪 除了一些冗余的內容，并修改了該工程的version和name的值，以與此例子的背景來符合。在目前情況下modelVersion值將被固定為 4.0.0，這也是Maven2唯一能夠識別的model版本。groupId，artifactId的值與創建工程時使用的命令中的相關屬性值是一致 的。packaging的值由工程的類型決定，如應用程序工程的packaging值為jar，Web應用工程的packaging值為war。上述情況 也可以從webapp的POM文件中看出，下面將看看這個pom的完整內容。
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0"><project>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <modelVersion>4.0.0</modelVersion>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <groupId>ce.demo.mvn</groupId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <artifactId>webapp</artifactId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <packaging>war</packaging>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <version>1.0</version>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <name>CE Maven Demo -- WebApp</name>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <dependencies>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">      <dependency>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">          <groupId>ce.demo.mvn</groupId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">          <artifactId>app</artifactId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">          <version>1.0</version>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">      </dependency>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <dependency>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        <groupId>javax.servlet</groupId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        <artifactId>servlet-api</artifactId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        <version>2.4</version>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        <scope>provided</scope>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    </dependency>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  </dependencies>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0"></project>
    比較app與webapp中的POM，除前面已經提過的packaging的差別外，我們還可以發現webapp中的POM多了dependencies 項。由于webapp需要用到app工程中的類(見HelloServlet源代碼)，它還需要javax.servlet包(因為該包并不默認存在于 jsdk中)。故，我們必須要將它們聲明到依賴關系中。
5.5 執行
    上述兩個工程創建完畢后，就需要執行一些命令來看看會有什么結果出現。我們首先進入app目錄，并執行命令mvn compile，然后會在該目錄下發現新生成的目錄target\classes，即編譯后的class文件(包括它的包目錄)就放在了這里。再執行命令mvn package，在目錄target中就會生成app-1.0.jar文件。該文件的全名由如下形式確定：artifactId-version.packaging。根據第2章的敘述可以知道，執行命令mvn package時，將首先將產生執行命令mvn compile之后的結果，故如果要打包，那么只需要執行mvn package即可。
    在app工程中執行完之后，就需要進入webapp工程了。進入webapp目錄，此次將只執行mvn package命令(隱示地執行了compile過程)。此次命令的執行并不成功，會出現如下問題：
D:\maven\demo\webapp>mvn package
……
Downloading: http://repo1.maven.org/maven2/ce/demo/mvn/app/1.0/app-1.0.pom
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] Error building POM (may not be this project's POM).
Project ID: ce.demo.mvn:app
Reason: Error getting POM for 'ce.demo.mvn:app' from the repository: Error transferring file
  ce.demo.mvn:app:pom:1.0
from the specified remote repositories:
  central (http://repo1.maven.org/maven2)
……
    由粗體內容可知，Maven正試圖從central倉庫下載app工程的artifact，但central倉庫肯定不會有這個artifact，其結果 只能是執行失敗!由第1章artifact名詞的解釋可知，被依賴的artifact必須存在于倉庫(遠程或本地)中，但目前webapp所依賴的app 必不存在于倉庫中，所以執行只能失敗。
    解決這個問題有兩種方法：[1]將app-1.0.jar安裝到倉庫中，使它成為一個artifact；[2]構建一個更高層次的工程，使app和webapp成為這個工程的子工程，然后從這個更高層次工程中執行命令。
    第一種方法比較簡單（見），此處將詳細討論第2種方法(見5.6節)。
5.6 更高層次工程
    我們可以將app和webapp的上一級目錄demo作為這兩個工程的 一個 更高層次工程，即使用app和webapp成為這個工程的子工程。為了使demo目錄成為一個demo工程，只需要在這個目錄下添加一個pom.xml文件，該文件內容如下：
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0"><project>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <modelVersion>4.0.0</modelVersion>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <groupId>ce.demo</groupId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <artifactId>mvn-demo</artifactId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <packaging>pom</packaging>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <version>1.0</version>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <name>CE Maven Demo</name>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">   
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <modules>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        <module>app</module>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        <module>webapp</module>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    </modules>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0"></project>
    與app和webapp中的POM相比，demo的POM使用了modules項，modules用于聲明本工程的子工程，module中的值對應于子工程的artifact名。而且該POM的packaging類型必須為pom。
    有了demo工程后，我們只需要在demo目錄下執行相關命令就可以了。通過如下命令即可驗證：
    [1]mvn clean – 消除工程(包括所有子工程)中產生的所有輸出。這本文的實例中，實際上是刪除target目錄。由于之前的操作只有app工程產生了target目錄，而webapp并沒有，所以將只會刪除app工程中的target目錄。
    [2]mvn package – 將工程制作成相應的包，app工程是作成jar包(app-1.0.jar)，webapp工程是作成war包(webapp-1.0.war)。打開 webapp-1.0.war包，可以發現app-1.0.jar被放到了WEB-INF的lib目錄中。
6 小結
    通過以上的敘述與實例，應該可以對Maven有一個粗略的認識了。使用Maven關鍵是要弄清楚如何寫pom.xml文件，就如同使用Ant要會寫 build.xml文件一樣。在POM中可以直接寫入Ant的task腳本，也可以調用Ant的build.xml文件(推薦)，所以Maven也可以完 成Ant的絕大多數工作(但不必安裝Ant)。注意：使用Maven就不要再過多的使用Ant腳本。
    利用好Maven的繼承特性及子工程的關系，可以很好地簡化POM文件，并能夠構建層次結構良好的工程，有利于工程的維護。
7 參考資源
[1]Maven官方網站. http://maven.apache.org
[2]Maven POM文件參考結構. http://maven.apache.org/ref/current/maven-model/maven.html
[3]Super POM. http://maven.apache.org/guides/introduction/introduction-to-the-pom.html
[4]Maven主要插件的列表. http://maven.apache.org/plugins
[5]Maven基本使用指南. http://maven.apache.org/guides/index.html
[6]Better Build with Maven. http://www.mergere.com/m2book_download.jsp -- 強烈推薦
[7]介紹Maven2. http://www.javaworld.com/javaworld/jw-12-2005 /jw-1205-maven_p.html
[8]揭秘Maven2 POM. http://www.javaworld.com/javaworld/jw-05-2006/jw-0529-maven.html
[9]Maven讓事情變得簡單. http://www-128.ibm.com/developerworks/cn/java/j-maven
[10]Maven文檔集. http://docs.codehaus.org/display/MAVENUSER/Home
[11]有效利用Maven2的站點生成功能. http://www.matrix.org.cn/resource/article/44/44491_Maven2.html
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