PHP and MySQL Web Development - P161 pptx

The next three lines are used to set up callback functions.We need to tell the parser what to do when it finds elements and character data inside the XML document.The call to xml_set_obj

After all these parameters are set, we call

$this->parseXML();

to actually do the work.The parseXML()method is shown in Listing 31.10.

Listing 31.10 parseXML() Method—Parsing the XML Returned from a Query

// Parse the XML into Product object(s) function parseXML()

{

$xml_parser = xml_parser_create();

xml_parser_set_option($xml_parser,XML_OPTION_SKIP_WHITE,1);

xml_set_object($xml_parser, $this);

xml_set_element_handler($xml_parser,

"startElementHandler",

"endElementHandler");

xml_set_character_data_handler($xml_parser, 'cdataHandler');

if (!($fp = fopen($this->_url, "r"))) {

die("could not open XML input");

} while ($data = fread($fp, 4096)) {

if (!xml_parse($xml_parser, $data, feof($fp))) {

die(sprintf("XML error: %s at line %d",

xml_error_string(xml_get_error_code($xml_parser)), xml_get_current_line_number($xml_parser)));

} } xml_parser_free($xml_parser);

}

In this method we are using PHP’s XML library, which is based on expat.

We begin by calling the xml_parser_create()function.This creates an instance of the parser and returns a handle to this parser, which will need to be passed to other func-tions.

We then need to set up a few things in this parser before we can actually parse the XML document, as follows:

xml_parser_set_option($xml_parser,XML_OPTION_SKIP_WHITE,1);

xml_set_object($xml_parser, $this);

xml_set_element_handler($xml_parser,

"startElementHandler",

"endElementHandler");

xml_set_character_data_handler($xml_parser, 'cdataHandler');

The first line sets the parser to skip whitespace (which will save effort).There are a few other options that can be set with this function, but this is the only one relevant here.

The next three lines are used to set up callback functions.We need to tell the parser what to do when it finds elements and character data inside the XML document.The call to xml_set_object()tells the parser that the callback functions will be found inside

$this, the current AmazonResultSetobject (If we were just using regular functions rather than class methods, we would not need this function call )

The call to xml_set_element_handler()tells the parser that whenever it finds the beginning of an element, it should call the method named startElementHandler(), and when it finds the end of an element, it should call the method named

endElementHandler().These are yet more methods we have written inside the

AmazonResultSetobject.These methods are called callbacks, and their signature must

fol-low a certain format.

The startElementHandler()method must accept three parameters: a reference to the parser, the name of the element that has just started, and an array of the attributes of the element.

The endElementHandler()method must accept two parameters: a reference to the parser, and the name of the element that is ending.

The call to xml_set_character_data_handler()tells the parser what to do when it encounters character data in the XML document.This will occur when the parser tries

to process the actual contents of an element It should call the method called

cDataHandler(), also located in the AmazonResultSetclass Again, this method must have a certain signature In this case, it must accept two parameters: a reference to the parser, and the character data as a string.We’ll look at the content of these callbacks in a moment.

After setting up all these parameters, we open the file at the URL we received a minute ago, and parse the XML we find there.The parser will work its way through the document, invoking the callback functions as it goes.

Finally, we need to clean up after ourselves by deleting the parser:

xml_parser_free($xml_parser);

Now, let’s see what happens in those callback functions.The three functions are shown

in Listing 31.11.

Listing 31.11 Callback Functions

// function to catch callbacks when the XML parser reaches the start of // a new element

function startElementHandler($parser, $name, $attributes) {

array_push($this->_names, $name);

if($name=='DETAILS')

$this->_currentProduct = new Product();

} if($name == 'BROWSENODE') {

$this->_currentProduct->_currentBrowseName++;

} if($name == 'CUSTOMERREVIEW') {

$this->_currentProduct->_currentReview++;

} }

// function to catch callbacks when the XML parser has data from // an element

function cdataHandler($parser, $cdata) {

$this->_currentName = array_slice($this->_names, -1, 1);

$this->_currentName = $this->_currentName[0];

switch($this->_currentName) {

case 'TOTALRESULTS' :

$this->_totalResults = $cdata;

break;

case 'DETAILS' : break;

case 'AUTHOR' :

$this->_currentProduct->authors[] = $cdata;

break;

case 'RATING' : case 'SUMMARY' : case 'COMMENT' :

@$this->_currentProduct->customerReviews[$this->_currentProduct->_

currentReview][$this->_currentName] = $cdata;

// fields that may contain returns and &s need to be concatenated // concatenation will give a notice if they are enabled -

//hence the @ break;

case 'LISTID' :

$this->_currentProduct->listIDs[] = $cdata;

Listing 31.11 Continued

case 'BROWSENAME' :

@$this->_currentProduct->

browseNames[$this->_currentProduct->_currentBrowseName] = $cdata;

// fields that may contain returns and &s need to be concatenated // concatenation will give a notice if they are enabled -

// hence the @ break;

case 'PRODUCT' :

$this->_currentProduct->similarProducts[] = $cdata;

break;

// there are certain keys we are dealing with the children of // separately so can ignore

case 'CUSTOMERREVIEW' : case 'AUTHORS' : case 'BROWSELIST' : case 'BROWSENODE' : case 'LISTS' : case 'REVIEWS' : case 'SIMILARPRODUCTS' : //do nothing

break;

default :

@$this->_currentProduct->nodes[$this->_currentName] = $cdata;

break;

} }

// function to get callbacks when the XML parser reaches the end of an // element

function endElementHandler($parser, $name) {

if($name=='DETAILS') {

//these are no longer required unset($this->_currentProduct->_currentReview);

unset($this->_currentProduct->_currentBrowseName);

array_push($this->_products, $this->_currentProduct);

} array_pop($this->_names) ; }

Listing 31.11 Continued

By reading through this code, you will see that these three functions populate the class member array $_productswith the information contained in the XML document.This array consists of instances of the Productclass, which we have created specifically to hold the details of an item.The code for the Productclass is shown in Listing 31.12. Listing 31.12 Part of Product.php—Storing Data on an Individual Item

<?php // This class holds data about a single amazon product // scalar attributes are all stored in the array nodes // attributes from the XML document that require special // treatment have their own array

// if the data came via XML/HTTP, most of the data will be in $this->nodes // if the data came via SOAP, _ALL_ of the data will be in $this->soap

// This class' main purpose is to provide a common interface to the data // from these two sources so all the display code can be common

class Product {

var $nodes = array();

var $authors = array();

var $listIDs = array();

var $browseNames = array();

var $customerReviews = array();

var $similarProducts = array();

var $_currentReview = -1;

var $_currentBrowseName = -1;

var $soap; // array returned by SOAP calls

// most methods in this class are similar // return the XML variable or the SOAP one // a single Product instance will only have one or the other function similarProductCount()

{ if($this->soap) return count($this->soap['SimilarProducts']);

else return count($this->similarProducts);

} This class consists almost entirely of accessor (get and set) functions, so we will not dwell

on it here.The main reason this class exists is so that we can conveniently store data from two different sources and access it through the same interface.This means we can take the default output from NuSOAP and an easy-to-parse result from the XML and store