XML Parsing

Data transferred in XML format must be parsed before being put in use. Generally, three types of elements in XML files need to be parsed: XML tags and tag values, XML attributes and attribute values, and 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

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.

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

3. 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.
   }
   

4. 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 as object as ArrayBuffer, '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 as object as ArrayBuffer, '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

In the following example, all parsing options are invoked 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 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
};
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