Current Location: Home> Latest Articles> How to parse and modify the namespace in an XML file using xml_set_end_namespace_decl_handler?

How to parse and modify the namespace in an XML file using xml_set_end_namespace_decl_handler?

gitbox 2025-05-20

In PHP, the xml_set_end_namespace_decl_handler function is a callback function that handles the end of a namespace declaration when XML parsing. It allows us to handle namespace changes during XML parsing, especially when parsing XML documents with namespaces, how to capture and modify namespace declarations.

1. Basic introduction to xml_set_end_namespace_decl_handler

The xml_set_end_namespace_decl_handler function is used to set a callback function that is called at the end of the namespace declaration when parsing XML. This callback function can be used to record the namespace changes or to perform necessary processing on the namespace.

2. Basic syntax of functions

 bool xml_set_end_namespace_decl_handler ( resource $parser , callable $handler )

  • $parser : XML parser resource, created through xml_parser_create .

  • $handler : The callback function called when the parser encounters the end of the namespace declaration.

3. Actual case: parse XML and modify namespace

Suppose we have an XML file containing some element with namespaces, and we want to capture namespace changes and modify them during parsing.

Here is a simple case showing how to parse XML using xml_set_end_namespace_decl_handler and modify its prefix at the end of the namespace.

 <?php
// create XML Parser
$parser = xml_parser_create();

// Define a callback function that ends with a namespace declaration
function endNamespaceDecl($parser, $prefix, $uri) {
    echo "Namespace ended: Prefix = '$prefix', URI = '$uri'\n";
    
    // Here we can modify the namespace，For example, replace a certain URI Or change the prefix
    if ($uri == "http://www.example.com/oldnamespace") {
        echo "Changing namespace URI\n";
        $uri = "http://www.gitbox.net/newnamespace";  // Replace with new URI
    }
}

// Set the callback function at the end of the namespace declaration
xml_set_end_namespace_decl_handler($parser, "endNamespaceDecl");

// XML Data Example
$xmlData = <<<XML
<root xmlns:old="http://www.example.com/oldnamespace">
    <old:item>Item 1</old:item>
</root>
XML;

// Analysis XML data
if (!xml_parse($parser, $xmlData, true)) {
    echo "XML Parsing error: " . xml_error_string(xml_get_error_code($parser)) . "\n";
    exit;
}

// 释放Parser
xml_parser_free($parser);
?>

4. Code description

  1. Create an XML parser : First use xml_parser_create to create an XML parser resource.

  2. Defining the callback function : We define a function called endNamespaceDecl , which will be called when the parser encounters the end of the namespace declaration. It outputs the prefix and URI of the currently ended namespace.

  3. Modify namespace : If we encounter the old namespace we defined (such as http://www.example.com/oldnamespace ), we can modify the namespace URI in the callback function (such as replace it with http://www.gitbox.net/newnamespace ).

  4. parse XML : We provide a piece of XML data with a namespace and start parsing the data through the xml_parse function.

  5. Release parser : After the parsing is completed, remember to release the parser resources.

5. Output result

When we run the above code, the output will show:

 Namespace ended: Prefix = 'old', URI = 'http://www.example.com/oldnamespace'
Changing namespace URI

This indicates that our callback function is fired at the end of the namespace declaration and we successfully modified the namespace URI.

6. Summary

Using the xml_set_end_namespace_decl_handler function allows us to capture the namespace changes when parsing XML data and modify the namespace if necessary. Through this method, you can flexibly process the namespace in XML documents, suitable for scenarios where XML namespaces need to be dynamically modified.

Related