Basic learning of XML

1.xml concept:

(1) Concept: XML (Extensible Markup Language: Extensible Markup Language) Extensible Markup Language

(2) Function: Store data--method: 1. Configuration file; 2. Transmission in the network.

(3) The difference between xml and html:

1.xml tags are all custom, html tags are predefined.

2.xml has strict syntax and html syntax is loose.

3.xml is for storing data, and html is for displaying data.

2. Syntax:

(1) Notes on xml creation:

1.xml file extension: .xml.

The first line of 2.xml must be defined as the document description.

There is only one root tag in the

3.xml document.

4. The attribute value must be enclosed in quotation marks (single and double).

5. Tags must be properly closed: with a head and tail, except for self-closing tags.

6.xml tag name.

Example:

//root tag

zhangsan

(2) Notes on custom tags:

1. The name can contain letters, numbers and other characters.

2. The name cannot start with a number or punctuation.

3. The name cannot start with the letters xml (or Xml, XML, etc.).

4. The name cannot contain spaces.

3. Constraints:

What is a constraint: specifies the writing rules of an xml document.

As a user (programmer) of the framework: 1. Be able to introduce constraint documents in xml; 2. Be able to simply read and understand constraint documents.

Categories:

1.DTD: a simple constraint technique, replaced;

2.Schema: A complex constraint technique.

4. Parsing XML

(1) Concept: operate the xml document and read the data in the document into the memory

Operating documents: 1. Parsing (reading): Read the data in the document into the memory; 2. Write: Save the data in the memory to the xml document for persistent storage.

How to parse xml:

1.DOM: Load the markup language document into the memory at one time, and form a dom tree in the memory (used on the server side):

Advantages: easy to operate, can perform all CRUD operations on the document

Disadvantage: takes up memory

2.SAX: read line by line, event-driven (mobile terminal use):

Advantages: no memory usage

Disadvantages: only read, can not add, delete or modify

(2) Common parsers for xml:

1.JAXP: The parser improved by sun company supports two ideas of dom and sax, but the performance is low and basically useless.

2.DOM4J: A very good parser, based on DOM.

3.3.Jsoup: Jsoup is a Java HTML parser that can directly parse a URL address and HTML text content.It enhances a very labor-saving API for fetching and manipulating data through DOM, CSS, and jQuery-like manipulation methods.

4.PULL: The built-in parser of the Android operating system, based on the sax method.