JavaScript 组件之旅（三）：用 Ant 构建组件_javascript技巧

听起来是不是很惬意？Let's go! 我们出发啦～

这期，我们会使用 Ant 将上期编写、整理的代码文件按指定的先后顺序合并成单一的源文件，然后压缩这个文件。这是构建 JavaScript 项目的基本步骤。Ant 是 Apache 的一个顶级开源项目，网上对它的介绍和安装，已经有很多文章，这里就不再赘述了。在构建之前，我们先来看看已有的文件布局：

 smart-queue <span style="COLOR: #c0c0c0">// 组件的根目录</span>
  +--- src <span style="COLOR: #c0c0c0">// JavaScript源文件目录</span>
    +--- lang.js <span style="COLOR: #c0c0c0">// 前文提到的“外部文件”</span>
    +--- smart-queue.js <span style="COLOR: #c0c0c0">// Smart Queue 主文件</span>

现在，我们要让它“丰满”起来：

• 组件根目录下添加：
  • README: 介绍 Smart Queue 组件
  • LICENSE: 组件的授权信息
  • build.xml: Ant 使用的配置文件
• 组件根目录下添加 lib 子目录：存放构建过程中需要使用的外部程序和库文件
  • lib 子目录下添加 yuicompressor.jar: 我们用 YUI Compressor 压缩 JavaScript
• 组件根目录下添加 test 子目录：存放测试组件所需的文件（下期介绍）
• src 目录下添加 intro.js: 介绍组件的版本及说明信息

麻雀虽小，五脏俱全。现在 Smart Queue 看上去像是比较专业的 JavaScript 项目了：

 smart-queue <span style="COLOR: #c0c0c0">// 组件的根目录</span>
  +--- lib <span style="COLOR: #c0c0c0">// JavaScript外部程序和库文件目录</span>
    +--- yuicompressor.jar <span style="COLOR: #c0c0c0">// YUI Compressor</span>
  +--- test <span style="COLOR: #c0c0c0">// 测试文件目录</span>
  +--- src <span style="COLOR: #c0c0c0">// JavaScript源文件目录</span>
    +--- intro.js <span style="COLOR: #c0c0c0">// 介绍和版本信息</span>
    +--- lang.js <span style="COLOR: #c0c0c0">// 前文提到的“外部文件”</span>
    +--- smart-queue.js <span style="COLOR: #c0c0c0">// Smart Queue 主文件</span>
  +--- README <span style="COLOR: #c0c0c0">// 组件自述文件</span>
  +--- LICENSE <span style="COLOR: #c0c0c0">// 组件授权信息</span>

我们计划将构建出来的文件存放到组件根目录下的 build 子目录，还要通过构建工具创建并销毁它。首次尝试构建前，建议先大概了解一下 Ant 的配置文件——build.xml 的结构：

<span style="COLOR: #b000b0"><span style="COLOR: #c00000">project</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"MyProject"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">default</span>=<span style="COLOR: #008000">"dist"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">basedir</span>=<span style="COLOR: #008000">"."</span><span style="COLOR: #b000b0">></span>
  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">description</span><span style="COLOR: #b000b0">></span>
    simple example build file
  <span style="COLOR: #b000b0"></span><span style="COLOR: #c00000">description</span><span style="COLOR: #b000b0">></span>
 <span style="COLOR: #707070"><span style="COLOR: #707070">-- set global properties for this build --</span><span style="COLOR: #707070">></span>
 <span style="COLOR: #b000b0"><span style="COLOR: #c00000">property</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"src"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">location</span>=<span style="COLOR: #008000">"src"</span><span style="COLOR: #b000b0">/></span>
 <span style="COLOR: #b000b0"><span style="COLOR: #c00000">property</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"build"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">location</span>=<span style="COLOR: #008000">"build"</span><span style="COLOR: #b000b0">/></span>
 <span style="COLOR: #b000b0"><span style="COLOR: #c00000">property</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"dist"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">location</span>=<span style="COLOR: #008000">"dist"</span><span style="COLOR: #b000b0">/></span>

 <span style="COLOR: #b000b0"><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"init"</span><span style="COLOR: #b000b0">></span>
  <span style="COLOR: #707070"><span style="COLOR: #707070">-- Create the time stamp --</span><span style="COLOR: #707070">></span>
  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">tstamp</span><span style="COLOR: #b000b0">/></span>
  <span style="COLOR: #707070"><span style="COLOR: #707070">-- Create the build directory structure used by compile --</span><span style="COLOR: #707070">></span>
  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">mkdir</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">dir</span>=<span style="COLOR: #008000">"${build}"</span><span style="COLOR: #b000b0">/></span>
 <span style="COLOR: #b000b0"></span><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0">></span>

 <span style="COLOR: #b000b0"><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"compile"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">depends</span>=<span style="COLOR: #008000">"init"</span>
<span style="COLOR: #b000b0">    </span><span style="COLOR: #0000c0">description</span>=<span style="COLOR: #008000">"compile the source "</span><span style="COLOR: #b000b0"> ></span>
  <span style="COLOR: #707070"><span style="COLOR: #707070">-- Compile the java code from ${src} into ${build} --</span><span style="COLOR: #707070">></span>
  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">javac</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">srcdir</span>=<span style="COLOR: #008000">"${src}"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">destdir</span>=<span style="COLOR: #008000">"${build}"</span><span style="COLOR: #b000b0">/></span>
 <span style="COLOR: #b000b0"></span><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0">></span>

 <span style="COLOR: #b000b0"><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"clean"</span>
<span style="COLOR: #b000b0">    </span><span style="COLOR: #0000c0">description</span>=<span style="COLOR: #008000">"clean up"</span><span style="COLOR: #b000b0"> ></span>
  <span style="COLOR: #707070"><span style="COLOR: #707070">-- Delete the ${build} and ${dist} directory trees --</span><span style="COLOR: #707070">></span>
  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">delete</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">dir</span>=<span style="COLOR: #008000">"${build}"</span><span style="COLOR: #b000b0">/></span>
  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">delete</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">dir</span>=<span style="COLOR: #008000">"${dist}"</span><span style="COLOR: #b000b0">/></span>
 <span style="COLOR: #b000b0"></span><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0">></span>
<span style="COLOR: #b000b0"></span><span style="COLOR: #c00000">project</span><span style="COLOR: #b000b0">></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>

仔细观察一下，除了 <font face="新宋体">name, description</font> 这些名字都很容易理解外，其他可以看到的规律包括：

• <font face="新宋体">project</font> 元素的 <font face="新宋体">default</font> 属性值对应某个 <font face="新宋体">target</font> 元素的 <font face="新宋体">name</font> 属性；
• <font face="新宋体">target</font> 元素的 <font face="新宋体">depends</font> 属性值对应其他某些 <font face="新宋体">target</font> 元素的 <font face="新宋体">name</font> 属性；
• <font face="新宋体">${somename}</font> 可以引用 <font face="新宋体">property</font> 中定义的值。

下面我们开始写自己的 build.xml.

首先，配置项目的基本信息，以及相关目录名称，将要使用的编码等等：

<span style="COLOR: #b000b0"><span style="COLOR: #c00000">project</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"Smart Queue"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">default</span>=<span style="COLOR: #008000">"compress"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">basedir</span>=<span style="COLOR: #008000">"."</span><span style="COLOR: #b000b0">></span>
  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">description</span><span style="COLOR: #b000b0">></span>Build file for Ant<span style="COLOR: #b000b0"></span><span style="COLOR: #c00000">description</span><span style="COLOR: #b000b0">></span>
  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">property</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"src"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">location</span>=<span style="COLOR: #008000">"src"</span><span style="COLOR: #b000b0"> /></span>
  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">property</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"build"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">location</span>=<span style="COLOR: #008000">"build"</span><span style="COLOR: #b000b0"> /></span>
  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">property</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"lib"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">location</span>=<span style="COLOR: #008000">"lib"</span><span style="COLOR: #b000b0">/></span>
  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">property</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"inputencoding"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">value</span>=<span style="COLOR: #008000">"utf-8"</span><span style="COLOR: #b000b0">/></span>
  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">property</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"outputencoding"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">value</span>=<span style="COLOR: #008000">"gbk"</span><span style="COLOR: #b000b0">/></span></span></span></span></span></span></span></span>

接着，定义一个用于初始化的 <font face="新宋体">target</font>, 它负责创建 build 子目录：

  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"init"</span><span style="COLOR: #b000b0">></span>
    <span style="COLOR: #b000b0"><span style="COLOR: #c00000">mkdir</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">dir</span>=<span style="COLOR: #008000">"${build}"</span><span style="COLOR: #b000b0">/></span>
  <span style="COLOR: #b000b0"></span><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0">></span></span></span>

然后定义名为 <font face="新宋体">concat</font> 的 <font face="新宋体">target</font>, 负责将 src 里的 3 个 JavaScript 文件按先后顺序连接起来。运行它要先运行前面定义的 <font face="新宋体">init</font>:

  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"concat"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">depends</span>=<span style="COLOR: #008000">"init"</span><span style="COLOR: #b000b0">></span>
    <span style="COLOR: #b000b0"><span style="COLOR: #c00000">concat</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">destfile</span>=<span style="COLOR: #008000">"${build}/smart-queue.source.js"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">encoding</span>=<span style="COLOR: #008000">"${inputencoding}"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">outputencoding</span>=<span style="COLOR: #008000">"${outputencoding}"</span><span style="COLOR: #b000b0">></span>
      <span style="COLOR: #b000b0"><span style="COLOR: #c00000">filelist</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">dir</span>=<span style="COLOR: #008000">"${src}"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">files</span>=<span style="COLOR: #008000">"intro.js, lang.js, smart-queue.js"</span><span style="COLOR: #b000b0"> /></span>
    <span style="COLOR: #b000b0"></span><span style="COLOR: #c00000">concat</span><span style="COLOR: #b000b0">></span>
  <span style="COLOR: #b000b0"></span><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0">></span></span></span></span>

这样，就可以得到一个可以工作的 JavaScript 文件，下面的 <font face="新宋体">target</font> 负责压缩这个文件，显然它依赖于 <font face="新宋体">concat</font>, 也依赖于 <font face="新宋体">init</font>, 但是不必显式指定对 <font face="新宋体">init</font> 的依赖——Ant 能处理这种依赖关系。这里调用 YUI Compressor 并传入适当的参数：

  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"compress"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">depends</span>=<span style="COLOR: #008000">"concat"</span><span style="COLOR: #b000b0">></span>
    <span style="COLOR: #b000b0"><span style="COLOR: #c00000">java</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">jar</span>=<span style="COLOR: #008000">"${lib}/yuicompressor.jar"</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">fork</span>=<span style="COLOR: #008000">"true"</span><span style="COLOR: #b000b0">></span>
      <span style="COLOR: #b000b0"><span style="COLOR: #c00000">arg</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">line</span>=<span style="COLOR: #008000">"--type js --charset utf-8 -o ${build}/smart-queue.js ${build}/smart-queue.js"</span><span style="COLOR: #b000b0">/></span>
    <span style="COLOR: #b000b0"></span><span style="COLOR: #c00000">java</span><span style="COLOR: #b000b0">></span>
  <span style="COLOR: #b000b0"></span><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0">></span></span></span></span>

大功告成，<font face="新宋体">compress</font> 处理后的文件就可以部署到生产系统上去了。最后我们做一下清理工作，使你在生成文件后还可以回到最初的状态:

  <span style="COLOR: #b000b0"><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">name</span>=<span style="COLOR: #008000">"clean"</span><span style="COLOR: #b000b0">></span>
    <span style="COLOR: #b000b0"><span style="COLOR: #c00000">delete</span><span style="COLOR: #b000b0"> </span><span style="COLOR: #0000c0">dir</span>=<span style="COLOR: #008000">"${build}"</span><span style="COLOR: #b000b0">/></span>
  <span style="COLOR: #b000b0"></span><span style="COLOR: #c00000">target</span><span style="COLOR: #b000b0">></span></span></span>

到此可以说基本的配置就写完了。怎么使用它呢？以命令行方式进入到组件根目录（或者说 build.xml 所在的目录），然后：

• 运行 <font face="新宋体">ant concat</font>, 将得到 ./build/smart-queue.source.js
• 运行 <font face="新宋体">ant</font>, 将选择 <font face="新宋体"><project></project></font> 中 <font face="新宋体">default</font> 引用的那个 <font face="新宋体">target</font>, 即 <font face="新宋体">compress</font>, 所以会得到 ./build 下的 smart-queue.source.js 和 smart-queue.js
• 运行 <font face="新宋体">ant clean</font>, 将删除 ./build 目录，回到最初的状态

这些前提是你已经正确安装或者说设置好了 JDK 和 Ant, 如果有错误提示出来，则可能需要检查它们是否已准备妥当。

一路看下来，是不是觉得本期介绍的东西很简单？那是当然了，构建工具就应该简单易用，否则把大量的时间花在那上面岂非不值？工具的价值在于提升生产力，从而创造更多价值。

最后，你可以在这里查看 Ant 的帮助文档（里面有很多好玩的东东哦），也可以在这里查看本期完整的 build.xml 文件。