XML Overview

XML is an extensible markup language (eXtensible Markup Language), the file extension .xml

Uses: description, data transmission

Use:

• Persistent data storage
• Data Exchange
• Configuration data

XML syntax and format

<?xml version="1.0" encoding="UTF-8" ?>
<! - comment format, beginning of the XML declaration ->
<! - There must be only one root element, case sensitive tag ->
<Students>
    <-! [] Attribute value in double quotes ->
    <Student id="2002">
        <! - tag pairs, and elements to be properly nested, nested allowed cross ->
        <name>Joe Smith</name>
        <age>28</age>
        <class>12 classes</class>
        <! - label-free body may be abbreviated ->
        <dcr/>
    </Student>
    <Student id="2003">
        <name>John Doe</name>
        <age>25</age>
        <class>14 classes</class>
    </Student>
</Students>

An XML element can contain letters, numbers and some other visible character, but must comply with some of the following specifications:

1. The name can contain letters, numbers and other characters
2. The name can not start with a number or punctuation
3. The name can not begin with the characters "xml" (or XML, Xml)
4. The name can not contain spaces
   browser verify the validity of the file format.

XML parsing

Analytical methods for the XML file:

1. Use DOM4J (DOM For Java) implement DOM parsing
2. JAXP Technology (abandoned)
3. SAX parsing
4. Pull resolution, similar to the SAX parsing

Compare DOM and SAX parsing mode

DOM parsing (Document Object Model) Document Object Model
(1) ease of use and strong, the use of DOM, XML documents will all information is stored in memory and simple traversal, supports XPath, enhanced ease of use
(2) inefficient, slow parsing, the memory footprint is too high, almost impossible to use for larger files,
(3) supported CRUD
SAX parsing (Simple API for Xml)
(1) to "push" event-driven model XML processing, although it is not W3C standards, but it is a widely accepted API
(2) The biggest advantage is the small memory consumption
(3) only for reading

Use DOM4J resolve

Dom4j is a simple, flexible open source library. Dom4j is a very good Java XML API, with excellent performance, powerful and extremely easy to use features.
Dom4j use development, need to download the appropriate Dom4j jar file.

How to use the project DOM4J
IDEA configuration:
create (1) a project folder lib
(2) copy the packet into the jar lib directory
(3) right-click on the folder lib -> Add as Library
Eclipse configuration:
create (1) a project folder lib
(2) copy the packet into the jar lib directory
(3) Right-click the jar package -> build path-> add to build path

Read and write operations to change deleted
DOM is a tree structure, XML above example, the root node is Students., Which is a leaf node Student, attribute child node is a child, it is also from the resolution process begins with the node, gradually resolved.

1, increase operational

// Create SAXReader class object, then use the read method to read
SAXReader reader = new SAXReader();
Document document= reader.read(new File("input.xml"));

// Get the root
Element root = document.getRootElement();

// add an element under the root
Element book = root.addElement("book");

// add the book value of the [property]
book.addAttribute("id", "1008");

// add a child node child
book.addElement("name").setText("" Jiuyangzhenjing "");
book.addElement("author").setText("Zhang Wuji");
book.addElement("price").setText("89.9");

// add the result still in memory, there needs to be written to a file
1 // Create output format
OutputFormat outputFormat = OutputFormat.createPrettyPrint();
outputFormat.setEncoding("utf-8");

// 2. Create a file format XMLWriter
XMLWriter writer = new XMLWriter(new FileWriter("input.xml"), outputFormat);

// 3. Write and Close
writer.write(document);
writer.close();

2, altered operation

1 // Create SaxReader
SAXReader reader = new SAXReader();
2 // Read
Document document = reader.read(new FileReader("input.xml"));
3 // Get the root
Element root = document.getRootElement();
// 4. Modify elements
List<Element> bookList = root.elements("book");
Element firstBook = bookList.get(0);
firstBook.element("price").setText("101");
Element secondBook = bookList.get(1);
secondBook.element("price").setText("120");
// 5. Delete the last
root.remove(bookList.get(bookList.size() - 1));
// 6. write file
OutputFormat format = OutputFormat.createPrettyPrint();
format.setEncoding("utf-8");
XMLWriter writer = new XMLWriter(new FileWriter("input.xml"), format);
// 7. Write
writer.write(document);
// 8. Close
writer.close();

3. Read Operation

public static void readxml() throws Exception{
	1 // create SaxReader
	SAXReader reader=new SAXReader();
	2 // Gets the Document object
	Document document=reader.read(new FileReader("src\\books2.xml"));
	// get the root node 3
	Element root=document.getRootElement();//books
	//System.out.println(root.getName());
	4 // get book collection, traversing get
	List<Element> bookList=root.elements("book");
	for (Element b : bookList) {
		// get 5 [property value]
		String id=b.attributeValue("id");
		// 6. obtaining sub-sub-node
		String name=b.element("name").getText();
		String author=b.element("author").getText();
		String price=b.elementText("price");
		Book book=new Book(Integer.parseInt(id), name, author, Double.parseDouble(price));
	    System.out.println(book.toString());
	}
}

The basic operation is the read SAXReader file, obtaining the root node, then the child element method to obtain child node and child nodes, etc., and finally write the file using XMLWriter

Failed to parse XML file problem

XML parsing failed, mainly because of problems caused by BOM header, seeFlow and the buffer flow conversion system using the - basic use

The solution is to use notepad ++ open, and then select "Use UTF-8 encoding", save it in the above "coding" option.