XML Parsing

When using XML as a data carrier, it is necessary to parse relevant elements in practice. This typically includes three types of operations: parsing XML tags and their values, parsing XML attributes and their values, and parsing XML event types and element information. For example, in web services, XML is the foundation of the Simple Object Access Protocol (SOAP). SOAP messages, which are usually encapsulated in XML format and contain request and response parameters, are parsed by web services to process client requests and generate corresponding responses.

The XML module provides the XmlPullParser class to parse XML text. The input is an ArrayBuffer or DataView that contains XML data, and the output is a structured parsing result.

Table 1 XML parsing options (see ParseOptions for detailed descriptions)

Precautions

• The input XML data must be in the standard format.

• Parsing a specified node is not supported.

Parsing XML Tags and Values

1. Import the module.

   import { xml, util } from '@kit.ArkTS'; // Use the API provided by the util module to encode text.
   

   ParsingTagsAndValues.ets

2. Create an XmlPullParser object.

   You can create an XmlPullParser object based on ArrayBuffer or DataView. Both methods yield the same results.

   let strXml: string =
     '<?xml version="1.0" encoding="utf-8"?>' +
       '<note importance="high" logged="true">' +
       '<title>Play</title>' +
       '<lens>Work</lens>' +
       '</note>';
   let textEncoder: util.TextEncoder = new util.TextEncoder();
   let arrBuffer: Uint8Array = textEncoder.encodeInto(strXml); // Encode data to prevent garbled Chinese characters.
   // Method 1: Create an XmlPullParser object based on ArrayBuffer.
   let xmlParser: xml.XmlPullParser = new xml.XmlPullParser(arrBuffer.buffer as object as ArrayBuffer, 'UTF-8');
   

   ParsingTagsAndValues.ets

   // Method 2: Create an XmlPullParser object based on DataView.
   let dataView: DataView = new DataView(arrBuffer.buffer as object as ArrayBuffer);
   let xmlParser: xml.XmlPullParser = new xml.XmlPullParser(dataView, 'UTF-8');
   

   ParsingTagsAndValues.ets

3. Customize a callback function. In this example, the callback function directly prints the tags and their values.

   function func(name: string, value: string): boolean {
     if (name == 'note') {
       console.info(name);
     }
     if (value == 'Play' || value == 'Work') {
       console.info('    ' + value);
       // ...
     }
     if (name == 'title' || name == 'lens') {
       console.info('  ' + name);
     }
     return true; // The value true means to continue parsing, and false means to stop parsing.
   }
   

   ParsingTagsAndValues.ets

4. Set parsing options and call the parseXml function.

   let options: xml.ParseOptions = {supportDoctype:true, ignoreNameSpace:true, tagValueCallbackFunction:func};
   xmlParser.parseXml(options);
   

   ParsingTagsAndValues.ets

   The output is as follows:

   note
     title
       Play
     title
     lens
       Work
     lens
   note
   

Parsing XML Attributes and Values

1. Import the module.

   import { xml, util } from '@kit.ArkTS'; // Use the util module to encode text.
   

   ParsingAttributesAndValues.ets

2. Create an XmlPullParser object.

   let strXml: string =
     '<?xml version="1.0" encoding="utf-8"?>' +
       '<note importance="high" logged="true">' +
       '    <title>Play</title>' +
       '    <title>Happy</title>' +
       '    <lens>Work</lens>' +
       '</note>';
   let textEncoder: util.TextEncoder = new util.TextEncoder();
   let arrBuffer: Uint8Array = textEncoder.encodeInto(strXml); // Encode data to prevent garbled Chinese characters.
   let xmlParser: xml.XmlPullParser = new xml.XmlPullParser(arrBuffer.buffer as object as ArrayBuffer, 'UTF-8');
   

   ParsingAttributesAndValues.ets

3. Customize a callback function. In this example, the callback function directly prints the attributes and their values.

   let str: string = '';
   function func(name: string, value: string): boolean {
     str += name + ' ' + value + ' ';
     return true; // The value true means to continue parsing, and false means to stop parsing.
   }
   

   ParsingAttributesAndValues.ets

4. Set parsing options and call the parseXml function.

   let options: xml.ParseOptions = {supportDoctype:true, ignoreNameSpace:true, attributeValueCallbackFunction:func};
   xmlParser.parseXml(options);
   console.info(str); // Print all attributes and their values.
   

   ParsingAttributesAndValues.ets

   The output is as follows:

   importance high logged true // Attributes and values of the note node
   

Parsing XML Event Types and Element Information

1. Import the module.

   import { xml, util } from '@kit.ArkTS'; // Use the util module to encode text.
   

   ParsingEventTypesAndElementInformation.ets

2. Create an XmlPullParser object.

   let strXml: string =
     '<?xml version="1.0" encoding="utf-8"?>' +
       '<note importance="high" logged="true">' +
       '<title>Play</title>' +
       '</note>';
   let textEncoder: util.TextEncoder = new util.TextEncoder();
   let arrBuffer: Uint8Array = textEncoder.encodeInto(strXml); // Encode data to prevent garbled Chinese characters.
   let xmlParser: xml.XmlPullParser = new xml.XmlPullParser(arrBuffer.buffer as object as ArrayBuffer, 'UTF-8');
   

   ParsingEventTypesAndElementInformation.ets

3. Customize a callback function. In this example, the callback function directly prints the event types and element depths.

   let str: string = '';
   function func(name: xml.EventType, value: xml.ParseInfo): boolean {
     str = name + ' ' + value.getDepth(); // Obtain the current depth of an element in the XML document.
     console.info(str);
     // ...
     return true; // The value true means to continue parsing, and false means to stop parsing.
   }
   

   ParsingEventTypesAndElementInformation.ets

4. Set parsing options and call the parseXml function.

   let options: xml.ParseOptions = {supportDoctype:true, ignoreNameSpace:true, tokenValueCallbackFunction:func};
   xmlParser.parseXml(options);
   

   ParsingEventTypesAndElementInformation.ets

   The output is as follows:

   0 0 // First digit 0: <?xml version="1.0" encoding="utf-8"?> corresponds to event type START_DOCUMENT, which value is 0; second digit 0: The depth is 0.
   2 1 // First digit 2: <note importance="high" logged="true"> corresponds to event type START_TAG, which value is 2; second digit 1: The depth is 1.
   2 2 // First digit 2: <title> corresponds to event type START_TAG, which value is 2; second digit 2: The depth is 2.
   4 2 // First digit 4: "Play" corresponds to event type TEXT, which value is 4; second digit 2: The depth is 2.
   3 2 // First digit 3: </title> corresponds to event type END_TAG, which value is 3; second digit 2: The depth is 2.
   3 1 // First digit 3: </note> corresponds to event type END_TAG, which value is 3; second digit 1: The depth is 1.
   1 0 // First digit 1: corresponds to event type END_DOCUMENT, which value is 1; second digit 0: The depth is 0.
   

Example Scenario

This example demonstrates how to use all parsing options to parse XML tags, attributes, and event types.

import { xml, util } from '@kit.ArkTS';
// ...
let strXml: string =
  '<?xml version="1.0" encoding="UTF-8"?>' +
    '<book category="COOKING">' +
    '<title lang="en">Everyday</title>' +
    '<author>Giana</author>' +
    '</book>';
let textEncoder: util.TextEncoder = new util.TextEncoder();
let arrBuffer: Uint8Array = textEncoder.encodeInto(strXml);
let xmlParser: xml.XmlPullParser = new xml.XmlPullParser(arrBuffer.buffer as object as ArrayBuffer, 'UTF-8');
let str: string = '';

function tagFunc(name: string, value: string): boolean {
  str = name + value;
  console.info('tag-' + str);
  return true;
}

function attFunc(name: string, value: string): boolean {
  str = name + ' ' + value;
  console.info('attri-' + str);
  return true;
}

function tokenFunc(name: xml.EventType, value: xml.ParseInfo): boolean {
  str = name + ' ' + value.getDepth();
  console.info('token-' + str);
  // ...
  return true;
}
// ...
  let options: xml.ParseOptions = {
    supportDoctype: true,
    ignoreNameSpace: true,
    tagValueCallbackFunction: tagFunc,
    attributeValueCallbackFunction: attFunc,
    tokenValueCallbackFunction: tokenFunc
  };
  xmlParser.parseXml(options);

The output is as follows:

tag-
token-0 0
tag-book
token-2 1
attri-category COOKING
tag-title
token-2 2
attri-lang en
tag-Everyday
token-4 2
tag-title
token-3 2
tag-author
token-2 2
tag-Giana
token-4 2
tag-author
token-3 2
tag-book
token-3 1
tag-
token-1 0