harmony 鸿蒙XML Generation

2023-10-30
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XML Generation

XML can be used as a data exchange format, which is supported by a wealth of systems and applications. For example, web services can transfer structured data in XML format.

XML can also be used as a message passing format for communication between nodes in a distributed system.

Precautions

XML tags must appear in pairs: one start tag and one end tag.
XML tags are case sensitive. The start tag and end tag must use the same case.

How to Develop

The xml module provides the XmlSerializer class to generate XML files. The input is an object of the ArrayBuffer or DataView type with a fixed length, which is used to store the output XML data.

You can call different to write different types of content. For example, call startElement(name: string) to write the start tag and setText(text: string) to write a tag value.

For details about the APIs of the XML module, see @ohos.xml (XML Parsing and Generation).

The following steps walk you through on how to generate an XML file.

Import the modules.

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

Create a buffer and create an XmlSerializer object, either based on an object of the ArrayBuffer or DataView type.

   // 1. Create an XmlSerializer object based on an object of the ArrayBuffer type.
   let arrayBuffer: ArrayBuffer = new ArrayBuffer(2048); // Create a 2048-byte object of the ArrayBuffer type.
   let thatSer: xml.XmlSerializer = new xml.XmlSerializer(arrayBuffer); // Create an XmlSerializer object based on the object of the ArrayBuffer type.

   // 2. Create an XmlSerializer object based on an object of the DataView type.
   let arrayBuffer: ArrayBuffer = new ArrayBuffer(2048); // Create a 2048-byte object of the ArrayBuffer type.
   let dataView: DataView = new DataView(arrayBuffer); // Use an object of the DataView type to operate the object of the ArrayBuffer type.
   let thatSer: xml.XmlSerializer = new xml.XmlSerializer(dataView); // Create an XmlSerializer object based on the object of the DataView type.

Call the functions to generate an XML file.

   thatSer.setDeclaration(); // Write the XML file declaration.
   thatSer.startElement('bookstore'); // Write the start flag.
   thatSer.startElement('book'); // Write the start tag of a nested element.
   thatSer.setAttributes('category', 'COOKING'); // Write the attributes and attribute values.
   thatSer.startElement('title');
   thatSer.setAttributes('lang', 'en');
   thatSer.setText('Everyday'); // Write the tag value.
   thatSer.endElement(); // Write the end flag.
   thatSer.startElement('author');
   thatSer.setText('Giada');
   thatSer.endElement();
   thatSer.startElement('year');
   thatSer.setText('2005');
   thatSer.endElement();
   thatSer.endElement();
   thatSer.endElement();

Use Uint8Array to operate the object of the ArrayBuffer type, and use TextDecoder to decode the Uint8Array.

   let view: Uint8Array = new Uint8Array(arrayBuffer); // Use Uint8Array to read data from the object of the ArrayBuffer type.
   let textDecoder: util.TextDecoder = util.TextDecoder.create(); // Call the TextDecoder class of the util module.
   let res: string = textDecoder.decodeWithStream(view); // Decode the view.
   console.info(res);

The output is as follows:

   <?xml version=\"1.0\" encoding=\"utf-8\"?><bookstore>\r\n  <book category=\"COOKING\">\r\n    <title lang=\"en\">Everyday</title>\r\n    <author>Giada</author>\r\n    <year>2005</year>\r\n  </book>\r\n</bookstore>