matlab.io.xml.dom.EntityResolver Class

Namespace: matlab.io.xml.dom

Abstract base class for entity resolvers

Since R2021a

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Description

matlab.io.xml.dom.EntityResolver is an abstract base class for deriving entity resolvers that resolve entity references encountered by a parser while parsing an XML file or string.

The matlab.io.xml.dom.EntityResolver class is a handle class.

Class Attributes

Abstract
true
ConstructOnLoad
true
HandleCompatible
true

For information on class attributes, see Class Attributes.

Methods

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Examples

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This example creates an entity resolver, configures a parser to use the resolver, and parses an XML file that includes an entity reference.

If the path of a file that contains an entity is specified relative to the location of the main XML document, a parser can use a default entity resolver to resolve the path. In this case, you do not have to define your own resolver. To make sure that a resolver is required for this example, the example saves the file that contains the entity and the main XML file in different folders at the same level.

In a subfolder chapters of the current folder, create a file chapter.xml that contains this markup for a chapter:

<?xml version="1.0" encoding="UTF-8"?>
<chapter><title color="red">Introduction</title></chapter>

In a subfolder books that is at the same level as the chapters folder, create a file books.xml that contains this markup for a book:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book [
<!ENTITY chapter SYSTEM "chapters/chapter.xml">
]>
<book>
    &chapter;
</book>

book.xml contains the entity reference &chapter; and declares that the resource for the entity is chapters/chapter.xml.

Define a subclass of the abstract class matlab.io.xml.dom.EntityResolver and name it BookEntityResolver. Save BookEntityResolver.m in the folder that contains the chapters and books folder.

classdef BookEntityResolver < matlab.io.xml.dom.EntityResolver
    
    properties
        BaseDir
    end
    
    methods
        
        function obj =  BookEntityResolver(baseDir)
            obj@matlab.io.xml.dom.EntityResolver()
            obj.BaseDir = baseDir;
        end
        
        function res = resolveEntity(obj,ri)
            import matlab.io.xml.dom.ResourceIdentifierType
            if getResourceIdentifierType(ri) == ResourceIdentifierType.ExternalEntity
                res = fullfile(obj.BaseDir, ri.SystemID);
            end
        end
    end
    
end

Create an entity resolver as an instance of the BookEntityResolver class.

import matlab.io.xml.dom.*

resolver = BookEntityResolver(pwd);

Create a parser and configure it to use the resolver.

p = Parser();
p.Configuration.EntityResolver = resolver;
p.Configuration.AllowDoctype = true;

Parse the file book.xml into a matlab.io.xml.dom.Document object.

filePath = "books/book.xml";
domDoc = parseFile(p,filePath);

To see that the chapter entity was resolved, find the chapter element node in the document.

nl = getElementsByTagName(domDoc,"chapter");
ch = node(nl,1)
ch = 
  Element with properties:

          TagName: 'chapter'
    HasAttributes: 0
      TextContent: 'Introduction'
         Children: [1×1 matlab.io.xml.dom.Element]

Version History

Introduced in R2021a

See Also

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