harmony 鸿蒙XML Parsing

  • 2023-10-30
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XML Parsing

Data transferred in XML format must be parsed in actual use. Generally, three types of elements need to be parsed, as described in Parsing XML Tags and Tag Values, Parsing XML Attributes and Attribute Values, and Parsing XML Event Types and Element Depths.

The xml module provides the XmlPullParser class to parse XML files. The input is an object of the ArrayBuffer or DataView type containing XML text, and the output is the parsed information.

Table 1 XML parsing options

Name Type Mandatory Description
supportDoctype boolean No Whether to ignore the document type. The default value is false, indicating that the document type is parsed.
ignoreNameSpace boolean No Whether to ignore the namespace. The default value is false, indicating that the namespace is parsed.
tagValueCallbackFunction (name: string, value: string) => boolean No Callback used to return tagValue, which consists of a tag and its value. The default value is null, indicating that XML tags and tag values are not parsed.
attributeValueCallbackFunction (name: string, value: string) => boolean No Callback used to return attributeValue, which consists of an attribute and its value. The default value is null, indicating that XML attributes and attribute values are not parsed.
tokenValueCallbackFunction (eventType: EventType, value: ParseInfo) => boolean No Callback used to return tokenValue, which consists of the event type and the attributes of parseInfo. The default value is null, indicating that the event type and the attributes of parseInfo are not parsed.

Precautions

  • To ensure successful XML parsing and conversion, the input XML data must comply with the standard format.

  • Currently, parsing a given node is not supported.

Parsing XML Tags and Tag Values

  1. Import the modules.

    import xml from '@ohos.xml';
    import util from '@ohos.util'; // Use the API provided by the util module to encode the file.
    
  2. Create an XmlPullParser object.

The XmlPullParser object can be created based on an object of the ArrayBuffer or DataView type.

```ts
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 the data to prevent garbled characters.
// 1. Create an XmlPullParser object based on an object of the ArrayBuffer type.
let that: xml.XmlPullParser = new xml.XmlPullParser(arrBuffer.buffer, 'UTF-8');

// 2. Create an XmlPullParser object based on an object of the DataView type.
let dataView: DataView = new DataView(arrBuffer.buffer);
let that: xml.XmlPullParser = new xml.XmlPullParser(dataView, 'UTF-8');
```
  1. Customize a callback function. In this example, the tag and tag value are directly printed.

    let str: string = '';
    function func(name: string, value: string): boolean {
      str = name + value;
      console.info(str);
      return true; // The value true means to continue parsing, and false means to stop parsing.
    }
    
  2. Set parsing options and call the parse() function.

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

    The output is as follows:

    note
    title
    Play
    title
    lens
    Work
    lens
    note
    

Parsing XML Attributes and Attribute Values

  1. Import the modules.

    import xml from '@ohos.xml';
    import util from '@ohos.util'; // Use the API provided by the util module to encode the file.
    
  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 the data to prevent garbled characters.
    let that: xml.XmlPullParser = new xml.XmlPullParser(arrBuffer.buffer, 'UTF-8');
    
  3. Customize a callback function. In this example, the attribute and attribute value are directly printed.

    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.
    }
    
  4. Set parsing options and call the parse() function.

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

The output is as follows:

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

Parsing XML Event Types and Element Depths

  1. Import the modules.

    import xml from '@ohos.xml';
    import util from '@ohos.util'; // Use the API provided by the util module to encode the file.
    
  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 the data to prevent garbled characters.
    let that: xml.XmlPullParser = new xml.XmlPullParser(arrBuffer.buffer, 'UTF-8');
    
  3. Customize a callback function. In this example, the event type and element depth are directly printed.

    let str: string  = '';
    function func(name: xml.EventType, value: xml.ParseInfo): boolean {
      str = name +' ' + value.getDepth(); // getDepth is called to obtain the element depth.
      console.info(str)
      return true; // The value true means to continue parsing, and false means to stop parsing.
    }
    
  4. Set parsing options and call the parse() function.

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

The output is as follows:

```
 0 0 // 0: <?xml version="1.0" encoding="utf-8"?>. The event type value of START_DOCUMENT is 0. 0: The depth is 0.
 2 1 // 2: <note importance="high" logged="true">. The event type value of START_TAG is 2. 1: The depth is 1.
 2 2 // 2: <title>. The event type value of START_TAG is 2. 2: The depth is 2.
 4 2 // 4: Play. The event type value of TEXT is 4. 2: The depth is 2.
 3 2 // 3: </title>. The event type value of END_TAG is 3. 2: The depth is 2.
 3 1 // 3: </note>. The event type value of END_TAG is 3. 1: The depth is 1 (corresponding to <note>).
 1 0 // 1: The event type value of END_DOCUMENT is 1. 0: The depth is 0.
```

Example Scenario

The following uses invoking all parsing options as an example to describe how to parse XML tags, attributes, and event types.

import xml from '@ohos.xml';
import util from '@ohos.util';

let strXml: string =
  '<?xml version="1.0" encoding="UTF-8"?>' +
    '<book category="COOKING">' +
    '<title lang="en">Everyday</title>' +
    '<author>Giada</author>' +
    '</book>';
let textEncoder: util.TextEncoder = new util.TextEncoder();
let arrBuffer: Uint8Array = textEncoder.encodeInto(strXml);
let that: xml.XmlPullParser = new xml.XmlPullParser(arrBuffer.buffer, '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
};
that.parse(options);

The output is as follows:

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

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