如何用PHP把RDF内容插入Web站点之中(4)

返回到类（Back To Class）c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e 既然你有这么大的权力，那么究竟为什么要把自己限制在仅仅是单个的ＲＤＦ来源呢？就象我早先说过的一样，大多数主要的站点都经常为他们所提供的内容做快照。其实将所有这些不同的来源插入到你的站点当中是相当简单的。让我们看看是如何做的。c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e 首先，我们把前面例子中的代码模块化。这样一来，你就无须为每一个单个的来源都一遍又一遍的重写相同的代码了。简化的方法就是将之打包成类，再把这个类包含到我的ＰＨＰ脚本当中。c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e 类代码如下：c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e<?class RDFParser{  //  // variables  //    // set up local variables for this class  var $currentTag = "";  var $flag = "";  var $count = 0;    // this is an associative array of channel data with keys("title", "link", "description")  var $channel = array();    // this is an array of arrays, with each array elementrepresenting an <item>  // each outer array element is itself an associative array   // with keys ("title", "link", "description")  var $items = array();     //  // methods  //   // set the name of the RDF file to parse  // this is usually a local file  // you may set it to a remote file if your PHP build supportsURL fopen()  function setResource($file)  {           $this->file = $file;  }     // parse the RDF file set with setResource()  // this populates the $channel and $items arrays  function parseResource()  {           // create parser           $this->xp = xml_parser_create();                      // set object reference           xml_set_object($this->xp, $this);                      // set handlers and parser options           xml_set_element_handler($this->xp, "elementBegin","elementEnd");           xml_set_character_data_handler($this->xp,"characterData");           xml_parser_set_option($this->xp,XML_OPTION_CASE_FOLDING, TRUE);           xml_parser_set_option($this->xp, XML_OPTION_SKIP_WHITE,TRUE);                      // read XML file           if (!($fp = fopen($this->file, "r")))            {                 die("Could not read $this->file");           }                      // parse data           while ($xml = fread($fp, 4096))            {               if (!xml_parse($this->xp, $xml, feof($fp)))                {                            die("XML parser error: " .xml_error_string(xml_get_error_code($this->xp)));               }           }                      // destroy parser           xml_parser_free($this->xp);  }   // opening tag handler  function elementBegin($parser, $name, $attributes)  {           $this->currentTag = $name;           // set flag if entering <channel> or <item> block           if ($name == "ITEM")           {                   $this->flag = 1;           }           else if ($name == "CHANNEL")           {                   $this->flag = 2;           }  }    // closing tag handler         function elementEnd($parser, $name)  {           $this->currentTag = "";             // set flag if exiting <channel> or <item> block           if ($name == "ITEM")           {                   $this->count++;                   $this->flag = 0;           }           else if ($name == "CHANNEL")           {                   $this->flag = 0;           }  }    // character data handler  function characterData($parser, $data)  {           $data = trim(htmlspecialchars($data));           if ($this->currentTag == "TITLE" || $this->currentTag =="LINK" || $this->currentTag == "DEscriptION")           {                   // add data to $channels[] or $items[] array                   if ($this->flag == 1)                   {  $this->items[$this->count][strtolower($this->currentTag)] .= $data;                   }                   else if ($this->flag == 2)                   {  $this->channel[strtolower($this->currentTag)] .= $data;                   }           }  }           // return an associative array containing channel information  // (the $channel[] array)  function getChannelInfo()  {           return $this->channel;  }   // return an associative array of arrays containing iteminformation  // (the $items[] array)  function getItems()  {           return $this->items;  } } ?>c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e 如果你对ＰＨＰ类较为熟悉的话，那么理解这段代码是相当容易的。如果不太懂的话，那么请直接跳到文章末尾的链接部分，看一篇关于类工作原理的好文章。然后在回来继续阅读上面的代码。c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e 在使用这个类之前，我要特别花几分钟指出其中的一行代码——即上面对xml_set_object()函数调用的那一行。c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e 现在的问题是如何使用这个类实际生成具有多个内容来源的Web页。c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e<?include("class.RDFParser.php");// how many items to display in each channel$maxItems = 5;?><html><head><basefont face="Verdana"><body> <table width="100%" border="0" cellspacing="5" cellpadding="5"> <tr><!-- first cell --><td valign=top align=left><font size="-1"><?// get and parse freshmeat.net channel$f = new RDFParser();$f->setResource("http://www.freshmeat.net/backend/fm-releases.rdf");$f->parseResource();$f_channel = $f->getChannelInfo();$f_items = $f->getItems();// now format and print it...?>The latest from <a href=<? echo $f_channel["link"]; ?>><? echo$f_channel["title"]; ?></a> <br> <ul> <? // iterate through items arrayfor ($x=0; $x<$maxItems; $x++) {  if (is_array($f_items[$x]))  {           // print data           $item = $f_items[$x];           echo "<li><a href=" . $item["link"] . ">" .$item["title"] . "</a>";  }}?></ul></font></td> <!-- second cell --><td align=center width=50%><i>Primary page content here</i></td> <!-- third cell --><td valign=top align=left><font size="-1"><?// get and parse slashdot.org channel$s = new RDFParser();$s->setResource("http://slashdot.org/slashdot.rdf");$s->parseResource();$s_channel = $s->getChannelInfo();$s_items = $s->getItems();// now format and print it...?>The latest from <a href=<? echo $s_channel["link"]; ?>><? echo$s_channel["title"]; ?></a> <br> <ul> <? // iterate through items arrayfor ($x=0; $x<$maxItems; $x++) {  if (is_array($s_items[$x]))  {           // print data           $item = $s_items[$x];           echo "<li><a href=" . $item["link"] . ">" .$item["title"] . "</a>";  }}?></ul></font></td> </tr></table> </body></head> </html>c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e  c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e 这段代码相当简单。一旦你用“new”关键字生成一个类的实例，c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e  $f = new RDFParser();c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e 那么就可以用类方法来设置要分析的RDF文件的位置，c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e$f->setResource("http://www.freshmeat.net/backend/fm-releases.rdf"); $f->parseResource();c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e 并且获取$channel和$items数组，以用于后面的处理。c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e  c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e<?$f_channel = $f->getChannelInfo();$f_items = $f->getItems();?> The latest from <a href=<? echo $f_channel["link"]; ?>><? echo$f_channel["title"]; ?></a> <br> <ul> <? // iterate through items arrayfor ($x=0; $x<$maxItems; $x++) {  if (is_array($f_items[$x]))  {           // print data           $item = $f_items[$x];           echo "<li><a href=" . $item["link"] . ">" .$item["title"] . "</a>";  }}?> </ul>c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e  c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e 每次你重新装入上面的脚本，相应的RDF文件就会被从特定的位置上取来，经过分析之后，按要求的格式显示出来。c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e 如果你站点具有高的访问量，你就可能觉得我们的辛苦无意义之极，尤其是当所用的RDF数据更新地没有那么快时，情况更糟。 在这种情况下，或许探究一下在本地缓存RDF数据才是较明智的做法：要么扩展上面的例子程序，在其中加入缓存功能；要么每阁几个小时都花很长的时间下载一个最新RDF文件的本地副本到你的Web服务器上，然后使用这个本地副本，而不是那个“活”的（the “live” one）。c hina it power . c omCBelzmR2KKFMNVzYrCnjicq0e
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