ajax的server部分(php版)

Server端的任务通常是根据Client的请求，进行逻辑操作，并将结果响应返回。这个响应通常为XML格式(因此server端需要使用PHP的DOM创建XML响应)

1.PHP使用DOM创建XML响应，供client端的JS解析然后在页面中显示;(因此需要熟练PHP的DOM API)
其实，PHP生成XML的方法有两种：
使用DOM API；（方法一）
另一种是直接将XML的内容echo出去即可；（方法二）
见示例：
HTML页面(包含三个JS触发函数：onmouseover, onmouseout, onclick; 分别触发自己的函数)
<!doctype html public "-//w3c//dtd html 4.0 tRANSITIONAL//en">
<html>
<head>
<title> Server PHP Ajax </title>
<script type="text/javascript" src="js.js"></script>
</head>

<body>
<span onmouseover="PHPechoXML()" onmouseout="PHPDOMXML()">Default Words</span>
<div id="show"></div>
divide<input type="text" id="firstNumber"/>by
<input type="text" id="secondNumber"/>
<input type="button" value="Send" onclick="CSparameter()"/>
<div id="result"></div>
</body>
</html>
JS页面(分别定义三个JS触发函数：PHPechoXML, PHPDOMXML, 以及CSparameter)
其中有XMLHttpRequest对象创建函数，以及各自的Server响应处理函数
///////1. 创建XMLHttpRequest对象
var xmlHttp = createXmlHttpRequestObject();

function createXmlHttpRequestObject()
...{
var xmlHttp;

try
...{
    // try to create XMLHttpRequest object
    xmlHttp = new XMLHttpRequest();
}
catch(e)
...{
    // assume IE6 or older
    var XmlHttpVersions = new Array('MSXML2.XMLHTTP.6.0',
                                    'MSXML2.XMLHTTP.5.0',
                                    'MSXML2.XMLHTTP.4.0',
                                    'MSXML2.XMLHTTP.3.0',
                                    'MSXML2.XMLHTTP',
                                    'Microsoft.XMLHTTP');
    for (var i=0; i<XmlHttpVersions.length && !xmlHttp; i++)
    ...{
      try

      ...{
        // try to create XMLHttpRequest object
        xmlHttp = new ActiveXObject(XmlHttpVersions[i]);
      }
      catch (e) ...{}
    }
}
if (!xmlHttp)
    alert("Error creating the XMLHttpRequest object.");
else
    return xmlHttp;
}

///////2. JavaScript事件响应函数(onmouseover触发)
// read a file from the server
function PHPechoXML()
...{
// only continue if xmlHttp isn't void
if (xmlHttp)
...{
    // try to connect to the server
    try
    ...{
      // initiate reading a file from the server
      //向Server端的PHPechoXML.php文件发送异步请求
      xmlHttp.open("GET", "PHPechoXML.php", true);
      xmlHttp.onreadystatechange = handleRequestStateChange;
      xmlHttp.send(null);
    }
    // display the error in case of failure
    catch (e)
    ...{
      alert("Can't connect to server: " + e.toString());
    }
}
}

///////3. JavaScript事件响应函数(onmouseout触发)
function PHPDOMXML()
...{
// only continue if xmlHttp isn't void
if (xmlHttp)
...{
    // try to connect to the server
    try
    ...{
      // initiate reading a file from the server
      //向Server端的PHPDOMXML.php文件发送异步请求
      xmlHttp.open("GET", "PHPDOMXML.php", true);
      xmlHttp.onreadystatechange = handleRequestStateChange;
      xmlHttp.send(null);
    }
    // display the error in case of failure
    catch (e)
    ...{
      alert("Can't connect to server: " + e.toString());
    }
}
}

// handles the response received from the server，Server端状态回调函数
function handleRequestStateChange()
...{

            //捕获IE和Opera潜在的错误
            if(!xmlResponse||!xmlResponse.documentElement)
            ...{
                throw("Invalid XML structure: "+xmlHttp.responseText);
            }
            //捕获FireFox的潜在错误
            var rootNodeName=xmlResponse.documentElement.nodeName;
            if(rootNodeName=="parsererror")
            ...{
                throw("Invalid XML structure: "+xmlHttp.responseText);
            }

            //获取Server端响应的XML响应并解析，到网页中显示
          // obtain the XML's document element
          xmlRoot = xmlResponse.documentElement;
          // obtain arrays with book titles and ISBNs
          cityArray=xmlRoot.getElementsByTagName("city");
          // generate HTML output
          var html = "";
          // iterate through the arrays and create an HTML structure
          for (var i=0; i<cityArray.length; i++)
            html += cityArray.item(i).firstChild.data + "<br/>";
          // obtain a reference to the <div> element on the page
          myDiv = document.getElementById("show");
          // display the HTML output
          myDiv.innerHTML = "Server says: <br />" + html;
      }
      catch(e)
      ...{
        // display error message
        alert("Error reading the response: " + e.toString());
      }
    }
    else
    ...{
      // display status message
      alert("There was a problem retrieving the data: " +
            xmlHttp.statusText);
    }
}
}

///////4. JavaScript事件响应函数(onclick触发)
function CSparameter()
...{
// only continue if xmlHttp isn't void
if (xmlHttp)
...{
    // try to connect to the server
    try
    ...{

    //获取form中的值
    var firstNumber=document.getElementById("firstNumber").value;
    var secondNumber=document.getElementById("secondNumber").value;

//设置为参数，对Server端的CSparameter.php进行异步请求
var param="firstNumber="+firstNumber+"&secondNumber="+secondNumber;

      // initiate reading a file from the server
      xmlHttp.open("GET", "CSparameter.php?"+param, true);
      xmlHttp.onreadystatechange = handleRequestStateChangePara;
      xmlHttp.send(null);
    }
    // display the error in case of failure
    catch (e)
    ...{
      alert("Can't connect to server: " + e.toString());
    }
}
}

//Server状态改变回调函数（Server端接受Client端传来的参数经过逻辑计算之后返回XML响应，Client端对XML进行解析，返回更新到页面中）
// handles the response received from the server
function handleRequestStateChangePara()
...{

if (xmlHttp.readyState == 4)
...{
    // continue only if HTTP status is "OK"
    if (xmlHttp.status == 200)
    ...{
      try
      ...{
          // read the message from the server
          var xmlResponse = xmlHttp.responseXML;

            //捕获IE和Opera潜在的错误
            if(!xmlResponse||!xmlResponse.documentElement)
            ...{
                throw("Invalid XML structure: "+xmlHttp.responseText);
            }
            //捕获FireFox的潜在错误
            var rootNodeName=xmlResponse.documentElement.nodeName;
            if(rootNodeName=="parsererror")
            ...{
                throw("Invalid XML structure: "+xmlHttp.responseText);
            }

          // obtain the XML's document element
          xmlRoot = xmlResponse.documentElement;

          cityArray=xmlRoot.getElementsByTagName("result");
          // generate HTML output
          var html = "";
          // iterate through the arrays and create an HTML structure
          for (var i=0; i<cityArray.length; i++)
            html += cityArray.item(i).firstChild.data + "<br/>";
          // obtain a reference to the <div> element on the page
          myDiv = document.getElementById("result");
          // display the HTML output
          myDiv.innerHTML = "Server says: <br />" + html;
      }
      catch(e)
      ...{
        // display error message
        alert("Error reading the response: " + e.toString());
      }
    }
    else
    ...{
      // display status message
      alert("There was a problem retrieving the data: " +
            xmlHttp.statusText);
    }
}
}

Server端的PHP脚本(负责接受Client端的异步请求做出响应，并以XML格式返回到Client端)
PHPechoXML.php（PHP生成XML响应的第一种方法，echo输出XML内容）
<?php
//server端的PHP生成XML文件的第一种方法，直接echo出XML
header('Content-Type: text/xml');
// generate XML header
echo '<?xml version="1.0" encoding="UTF-8" standalone="yes"?>';

echo '<cities>';
$cityArray=array('Paris','London','NewYork','Beijing','Tokoy');
foreach ($cityArray as $city)
{
echo '<city>'.$city.'</city>';
}
echo '</cities>';

PHPDOMXML.php(PHP生成XML响应的第二种方法，使用PHP的DOM API，输出XML格式的响应)
<?php
header('Content-Type: text/xml');

$cityArray=array('Shanghai','Beijing','Shanxi','Shandong');
//创建一个XML文档
$dom=new DOMDocument();
//最外层的Tag
$citiesTag=$dom->createElement('cities');
$dom->appendChild($citiesTag);
//里面的Tag可以通过循环产生
foreach ($cityArray as $city)
{
    $cityTag=$dom->createElement('city');
    $cityName=$dom->createTextNode($city);
    $cityTag->appendChild($cityName);
    $citiesTag->appendChild($cityTag);
}
//将XML结构保存为字符串并输出
$xmlString=$dom->saveXML();
echo $xmlString;
?>

2. client端的与Server端的参数传递：
client端的网页中可以有form，这样可以将参数传递到server端<GET或POST方法，变量或XML>，server端根据传递的参数，生成满足要求的XML响应；(实现了client端和server端的参数交互)
见示例：
与1中一样，参数传递的PHP端的脚本如下CSparameter.php(接受Client端form异步请求的参数，进行逻辑处理，并生成XML响应发回Client端)<?php
//自定义Server端的错误处理函数
require_once('error_handler.php');
header('Content-Type: text/xml');

//接受Client端异步请求的参数
$firstNumber=$_GET['firstNumber'];
$secondNumber=$_GET['secondNumber'];

//进行逻辑计算
$result=$firstNumber/$secondNumber;

//生成XML格式的响应向Client端返回
$dom=new DOMDocument();
$resultsTag=$dom->createElement('results');
$dom->appendChild($resultsTag);

$resultTag=$dom->createElement('result');
$resultText=$dom->createTextNode($result);
$resultTag->appendChild($resultText);
$resultsTag->appendChild($resultTag);

$xmlString=$dom->saveXML();
echo $xmlString;

?>
3. PHP端的错误异常(这里说的错误或异常都是指逻辑错误)处理：
a)PHP默认情况下，发生错误或异常的时候，不会将异常抛出(这是因为php.ini中display_errors的默认置为off,错误将被保存在Apache错误日志记录中)，因此编写起来很难调试。<往往浏览器显示的错不太容易定位>

b)但如果将display_errors设置为on后，错误将显示出来，但是不友好的出错信息.

c)可以编写自己的PHP错误异常处理函数(不一定要求display_errors设置为on)，将错误以明显的方式显示出来，便于调试；
通常自己编写异常处理函数如下：
显示定义的Server端错误异常抛出函数error_handler.php(PHP程序中可以方便地复用)
<?php
//set a user-defined error handler function用户自定义出错异常处理方法
set_error_handler('error_handler', E_ALL);
function error_handler($errNo,$errStr,$errFile,$errLine)
{
    //如果输出缓存非空，将其置空
    if(ob_get_length()) ob_clean();
    //定义自定义输出
    $error_message='ERRNO: '.$errNo.chr(10).'TEXT: '.$errStr.chr(10).'LOCATION: '.$errFile.', Line'.$errLine;
    echo $error_message;
    exit;
}
?>

4.server端存取数据库<使用MySQL存取数据，从而实现真正的动态>
这个已经很经典了，可以使用MySQL或MSSQL、Oracle等
a）打开数据库；b)SQL语句Query c)关闭数据库

5.server端PHP程序封装和体系结构(server端php程序引入设计模式)
a) appname.php <接受client端请求>
b) appname.class.php <将server端的逻辑、数据库操作、错误处理等封装成类，包含属性、方法、构造函数、析构函数>
c) config.php
d) error_handler.php

一个server端引入设计模式的例子：(设计Server端PHP脚本的程序架构，增强扩展性和重用性)
一个很简单的Keywords Suggest程序：(包括index.html, css/style.css, js.js以及PHP代码php/suggest.php, suggest.class.php, error_handler.php, config.php 支持数据库)
index.html(css/style.css, js.js; 注意两个JS客户端事件触发onkeyup,onclick)
onkeyup在用户输入的时候实时异步地向Server端发送请求，Server给出响应；onclick在用户点击search的时候，向Server发送请求
<!doctype html public "-//w3c//dtd html 4.0 tRANSITIONAL//en">
<html>
<head>
<title> Design Pattern PHP AJAX (keywords suggest DEMO) </title>
<link type="text/css" rel="stylesheet" href="css/style.css"/>
<script type="text/javascript" src="js.js"></script>
</head>
<body>
    <noscript>
        <strong>This example requires a JavaScript-enabled browser!</strong>
    </noscript>
    <div class="project">
        <span class="title">Welcome to Design Pattern PHP AJAX (keywords suggest DEMO) </span>
        <br />
        <br />
        <div class="news">
        <br /><input type="text" id="keyword" onkeyup="keyup()" /><input type="button" id="search" onclick="search()" value="search"><br /><br />
            suggest keywords:
            <div id="show"></div>
        </div>
    </div>
</body>
</html>
css/style.css
body
{...}{
    font-family: Arial;
    font-size: small;
    background-color: #fff;
}
.title
{...}{
    font-size:x-large;
}
div.project
{...}{
    background-color: #99ccff;
    padding:5px;
    border:#000099 1px solid;
}
div.news
{...}{
    background-color:#fffbb8;
    padding:2px;
    border: 1px dashed;
}
#show
{...}{
    color: #008000;
    font-style: italic;
}js.js(JS中定义响应函数以及Client处理Server响应的回调函数)
///////////////////////////////////////////////////////////
//1.创建XMLHttpRequest对象
///////////////////////////////////////////////////////////
var xmlHttp = createXmlHttpRequestObject();
function createXmlHttpRequestObject()
...{
var xmlHttp;
try
...{
    // try to create XMLHttpRequest object
    xmlHttp = new XMLHttpRequest();
}
catch(e)
...{
    // assume IE6 or older
    var XmlHttpVersions = new Array('MSXML2.XMLHTTP.6.0',
                                    'MSXML2.XMLHTTP.5.0',
                                    'MSXML2.XMLHTTP.4.0',
                                    'MSXML2.XMLHTTP.3.0',
                                    'MSXML2.XMLHTTP',
                                    'Microsoft.XMLHTTP');
    for (var i=0; i<XmlHttpVersions.length && !xmlHttp; i++)
    ...{
      try

      ...{
        // try to create XMLHttpRequest object
        xmlHttp = new ActiveXObject(XmlHttpVersions[i]);
      }
      catch (e) ...{}
    }
}
if (!xmlHttp)
    alert("Error creating the XMLHttpRequest object.");
else
    return xmlHttp;
}

//向id为show的div显示server端响应的正确
function display(message)
...{
    showDIV=document.getElementById("show");
    showDIV.innerHTML=message;
}
//向id为show的div显示server端响应的错误信息
function displayError(errormessage)
...{
    //显示出错信息
    display("Error retrieving the new message!<br/>"+errormessage);
}

///////////////////////////////////////////////////////////
//2. event-driven函数(keyup函数)
///////////////////////////////////////////////////////////
var keyupAddress="php/suggest.php?action=keyup&keyword=";
function keyup()
...{
    if(xmlHttp)
    ...{
        //server不忙的时候发送异步请求
        if(xmlHttp.readyState==0||xmlHttp.readyState==4)
        ...{
            try
            ...{
                var keyword=document.getElementById("keyword").value;
                //发出异步请求
                xmlHttp.open("GET",keyupAddress+keyword,true);
                xmlHttp.onreadystatechange=handlereadystatechange;
                xmlHttp.send(null);
            }
            catch(e)
            ...{
                displayError(e.toString);
            }
        }
    }
}
///////////////////////////////////////////////////////////
//3. 回调函数,server端响应状态发生变化后激发该函数
///////////////////////////////////////////////////////////
function handlereadystatechange()
...{
    if(xmlHttp.readyState==4)
    ...{
        if(xmlHttp.status==200)
        ...{
            try
            ...{
                //获取server端响应
                var xmlResponse = xmlHttp.responseXML;
                suggestArray=xmlResponse.getElementsByTagName("suggest");
                var showText="";
                for(var i=0;i<suggestArray.length;i++)
                ...{
                    var textNodes=suggestArray[i].getElementsByTagName("text");
                    var timesNodes=suggestArray[i].getElementsByTagName("times");
                    for(var j=0;j<textNodes.length;j++)
                    ...{
                        showText+=textNodes[j].childNodes[0].nodeValue+" ("+timesNodes[j].childNodes[0].nodeValue+") <br />";
                    }
                }
                //显示响应到页面中
                display(showText);
            }
            catch(e)
            ...{
                displayError(e.toString());
            }
        }
    }
}
///////////////////////////////////////////////////////////
//2. event-driven函数(search函数)
///////////////////////////////////////////////////////////
var searchAddress="php/suggest.php?action=search&keyword=";
function search()
...{
    if(xmlHttp)
    ...{
        //server不忙的时候发送异步请求
        if(xmlHttp.readyState==0||xmlHttp.readyState==4)
        ...{
            try
            ...{
                var keyword=document.getElementById("keyword").value;
                //发出异步请求
                xmlHttp.open("GET",searchAddress+keyword,true);
                xmlHttp.onreadystatechange=handlereadystatechange;
                xmlHttp.send(null);
            }
            catch(e)
            ...{
                displayError(e.toString);
            }
        }
    }
}

最后注意：Server端PHP脚本的程序架构(suggest.php为Server端的主要处理函数，另外suggest.class.php,error_handler.php,config.php等)
suggest.php(获取Client端的参数，并调用suggest类的两个方法，生成XML格式的响应发回到Client端)
<?php
require_once('suggest.class.php');
header('Content-Type: text/xml');
//确定用户浏览器不会缓存结果
header('Expires: Wed, 23 Dec 1980 00:30:00 GMT');
header('Last-Modified: '.gmdate('D, d M Y H:i:s').' GMT' );
header('Cache-Control: no-cache, must-revalidate');
header('Pragma: no-cache');

$action=$_GET['action'];
$keyword=$_GET['keyword'];

$oSuggest=new suggest();
if($action=='keyup'&&$keyword!='')
{
    $suggestXML=$oSuggest->getSuggests($keyword);
}
if($action=='search'&&$keyword!='')
{
    $suggestXML=$oSuggest->submitKeyword($keyword);
}
echo $suggestXML;
?>suggest.class.php类
<?php
require_once('error_handler.php');
require_once('config.php');
class suggest
{
    //成员变量
    private $conn;

    //构造函数, 数据库链接
    function __construct()
    {
        $this->conn=new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_DATABASE);
        if (mysqli_connect_errno()) {
            printf("Connect failed: %s ", mysqli_connect_error());
            exit();
        }
    }
    //析构函数,断开数据库链接
    function __destruct()
    {
        $this->conn->close();
    }
    //getSuggests成员函数(该函数主要响应Client端action=keyup，即用户正在输入时候的异步请求)
    public function getSuggests($keyword)
    {
        //产生suggest(产生数据库中与所输入关键词前半部分相同的关键词)
        $suggest_query='select * from keywords where keyword like ''.$keyword.'%' order by times desc limit 5';
        $suggest_result=$this->conn->query($suggest_query);
        $suggest_num=$suggest_result->num_rows;

        $strOUT='<?xml version="1.0" encoding="UTF-8" standalone="yes"?>';
        if($suggest_num==0)
        {
            //$strOUT=$strOUT.'<suggests><suggest><text>'.$keyword.'</text><times>0</times></suggest></suggests>';
        }
        else
        {
            $strOUT=$strOUT."<suggests>";
            for($i=0;$i<$suggest_num;$i++)
            {
              $suggest_row = $suggest_result->fetch_row();
              $strOUT=$strOUT.'<suggest><text>'.$suggest_row[1].'</text><times>'.$suggest_row[2].'</times></suggest>';
            }
           $strOUT=$strOUT.'</suggests>';
        }
       return $strOUT;
    }
    //submitKeyword成员函数(该函数主要响应Client端action=search，即用户点击search时候的异步请求)
    public function submitKeyword($keyword)
    {
        $select_query='select * from keywords where keyword=''.$keyword.''';
        $select_result=$this->conn->query($select_query);
        $select_num=$select_result->num_rows;

        //遇到新的keywords添加到数据库中，遇到已有的keywords增加次数
        $strOUT='<?xml version="1.0" encoding="UTF-8" standalone="yes"?>';
        //已经存在,增加次数
        if($select_num!=0)
        {
            $select_row = $select_result->fetch_row();
            $times_now=$select_row[2];
            $times_now=$times_now+1;
            $update_query='update keywords set times ='.$times_now.' where keyword=''.$keyword.''';
            $update_result=$this->conn->query($update_query);
            $strOUT=$strOUT.'<suggests><suggest><text>'.$keyword.'</text><times>'.$times_now.'</times></suggest></suggests>';
        }
        else
        {
        //不存在保存插入
            $insert_query='insert into keywords(keyword, times) values (''.$keyword.'',1)';
            $insert_result=$this->conn->query($insert_query);
            $strOUT=$strOUT.'<suggests><suggest><text>'.$keyword.'</text><times>1</times></suggest></suggests>';
        }
       return $strOUT;
    }
}
?>
最后两个函数，config.php保存应用程序配置信息(如数据库配置信息)
<?php
define('DB_HOST', 'localhost');
define('DB_USER','phpajaxuser');
define('DB_PASSWORD','phpajaxuser');
define('DB_DATABASE','phpajax');
?>
error_handler.php保存自定义异常处理
<?php
//设置用户自定义错误处理函数
set_error_handler('error_handler', E_ALL);

function error_handler($errNo,$errStr,$errFile,$errLine)
{
if(ob_get_length()) ob_clean();

    $error_message='ERRNO: '.$errNo.chr(10).'TEXT: '.$errStr.chr(10).'LOCATION: '.$errFile.' Line: '.$errLine;
    echo $error_message;
    exit;
}
?>最后还需要sql语句向数据库中添加用于保存keywords的database
CREATE TABLE `keywords` (
`id` int(10) unsigned NOT NULL auto_increment,
`keyword` varchar(32) NOT NULL default '',
`times` int(10) unsigned NOT NULL default '0',
PRIMARY KEY (`id`)
) TYPE=MyISAM AUTO_INCREMENT=1 ;

6.关于PHP的小知识，以后研究：
PHP从远程服务器读取数据的方法(有点儿类似Web Crawl)：
file_get_contents;
或者CURL<Client URL Library>www.php.net/curl

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