什么是Node.js?Node.js详细介绍(2)

实际上,服务器端和客户端没有任何区别。没错,这没有按钮点击操作,也没有向文本字段键入的操作,但在一个更高的层面上,事件正在 发生。一个连接被建立 — 事件!数据通过连接接收 — 事件!数据通过连接停止 — 事件!

为什么这种设置类型对 Node 很理想?JavaScript 是一种很棒的事件驱动编程语言,因为它允许匿名函数和闭包,更重要的是,任何写过代码的人都熟悉它的语法。事件发生时调用的回调函数可以在捕获事件处编写。这样,代码容易编写和维护,没有复杂的面向对象框架,没有接口,没有在上面架构任何内容的潜能。只需监听事件,编写一个回调函数,然后,事件驱动编程将照管好一切!


示例 Node 应用程序

最后,我们来看一些代码!让我们将讨论过的所有内容综合起来,创建我们的第一个 Node 应用程序。由于我们已经知道,Node 对于处理高流量应用程序很理想,我们就来创建一个非常简单的 web 应用程序 — 一个为实现最大速度而构建的应用程序。下面是 “老板” 交代的关于我们的样例应用程序的具体要求:创建一个随机数字生成器 RESTful API。这个应用程序应该接受一个输入:一个名为 “number” 的参数。然后,应用程序返回一个介于 0 和该参数之间的随机数字,并将生成的数字返回调用者。由于 “老板” 希望它成为一个广泛流行的应用程序,因此它应该能处理 50,000 个并发用户。我们来看看代码:

清单 2. Node 随机数字生成器

复制代码 代码如下:


// these modules need to be imported in order to use them.
// Node has several modules.  They are like any #include
// or import statement in other languages
var http = require("http");
var url = require("url");

// The most important line in any Node file.  This function
// does the actual process of creating the server.  Technically,
// Node tells the underlying operating system that whenever a
// connection is made, this particular callback function should be
// executed.  Since we're creating a web service with REST API,
// we want an HTTP server, which requires the http variable
// we created in the lines above.
// Finally, you can see that the callback method receives a 'request'
// and 'response' object automatically.  This should be familiar
// to any PHP or Java programmer.
http.createServer(function(request, response) {

     // The response needs to handle all the headers, and the return codes
     // These types of things are handled automatically in server programs
     // like Apache and Tomcat, but Node requires everything to be done yourself
     response.writeHead(200, {"Content-Type": "text/plain"});

     // Here is some unique-looking code.  This is how Node retrives
     // parameters passed in from client requests.  The url module
     // handles all these functions.  The parse function
     // deconstructs the URL, and places the query key-values in the
     // query object.  We can find the value for the "number" key
     // by referencing it directly - the beauty of JavaScript.
     var params = url.parse(request.url, true).query;
     var input = params.number;

     // These are the generic JavaScript methods that will create
     // our random number that gets passed back to the caller
     var numInput = new Number(input);
     var numOutput = new Number(Math.random() * numInput).toFixed(0);

     // Write the random number to response
     response.write(numOutput);

     // Node requires us to explicitly end this connection.  This is because
     // Node allows you to keep a connection open and pass data back and forth,
     // though that advanced topic isn't discussed in this article.
     response.end();

   // When we create the server, we have to explicitly connect the HTTP server to
   // a port.  Standard HTTP port is 80, so we'll connect it to that one.
}).listen(80);

// Output a String to the console once the server starts up, letting us know everything
// starts up correctly
console.log("Random Number Generator Running...");

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