XML Extensible Markup Language

XML Extensible Markup Language

1. Concept:

XML was originally intended to replace HTML, tag names can be defined directly, cannot be used to start with a numeric case-sensitive, use a configuration file to encapsulate data

Because XML is well-formed, it is widely used, such as data-exchange data configuration for persistent storage data

the difference between XML and HTML :

1) The HTML tag is fixed and cannot be extended. XML tags are not fixed and extensible.

2) HTML focuses on the information displayed. XML focuses on the structure of identifying information.

3) HTML is case-insensitive. XML is case-sensitive. XML syntax is more rigorous than HTML.

2. Components

Document declaration: <?xml version= "1.0" encoding= "Utf-8"?>

Must top line shelf Write

Root tag: has and has only one root tag

Other Tags: have a start tag must have an end tag

Tag properties: A label can have multiple properties, each with its own name and value, for example: <student name= "Text" >

Annotations:<!---->//comment Annotation objects

tags in the contents of Egg Zhang San:<name> Zhang San </name>

All whitespace and line breaks appear in the XML tag, and the XML parser is treated as a label content

3. Analytic thinking

Dom parsing thought: Document Object Model (DOM4J parsing)

Load the document into memory once and then extract the parts of the document as objects

Pros: Ability to add and revise documents

Disadvantage: Memory consumption is suitable for PC side

Sax parsing thought: Parsing based on events, reading one row at a time, releasing a line (sax parsing, pull parsing)

Pros: No memory available for mobile

Disadvantages: can only be found and deleted changes

Second, dom4j analysis

To read the XML file step:

1. Import dom4j jar Package

2. Creating the Parser Object

Saxreader reader = new Saxreader ();

Document doc = Reader.read (new FileInputStream ("XML file name. xml"));

3. Get the root Tag object

Element rootelement = Doc.getrootelement ();

1)Rootelement.node (the first few nodes);//Get a single Node object

Gets the child node under the root tag (cannot get the grandson node), the white space is also counted as a child node object

Rootelement.nodeiterator ();//Get Multiple Node objects

2)rootelement.element ("label name");//Gets the first child label object

Rootelement.elements ();//Get All Child label objects

Rootelement.elementiterator ();//Gets all the child label objects by means of iterators

4. Get the Tag Property object

Element element = rootelement.element ("label name");

Attribute Attribute = Element.attribute (the first few attributes/"attribute names");

Attribute.getname ();//Gets the key of the property

Attribute.getvalue ();//Gets the value of the property

Element.attributes (); Get all Property objects

Element.attributeiterator (); Gets all the property objects by means of iterators

Element.attributevalue (the first few attributes/"attribute names"); Get the value of the Property object directly

5. Get the text inside the tag

list<element> list = Element.elements ();

for (Element ele:list) {

String text = Ele.gettext ();//Get text content

System.out.println (text);

}

To write the XML file in code step:

Importing dom4j jar Packages

Through the documentation Help class create Docdocument doc = Documenthelper.createdocument ();//Add a root tag element rootele = doc.addelement ("Students ");//Add a sub-label element ele = rootele.addelement (" student ");//Add an attribute Ele.addattribute (" id "," 9527 ") to the student tag;// Add a name and school number label and content to student element element1 = ele.addelement ("sname"); Element1.addtext ("Zhang San"); Element Element2 = ele.addelement ("Sid"), Element2.addtext ("007"),//writes the In-memory doc to the hard disk outputformat FORMAT1 = Outputformat.createcompactformat (); OutputFormat format2 = Outputformat.createprettyprint (); Beautiful format//in the development phase to facilitate our debugging can use beautiful format//project developed well after the line, we want to adjust to compact format to reduce the volume of the XML file XMLWriter writer = new XMLWriter (New FileOutputStream ( "Mydoc.xml"), FORMAT2); Writer.write (doc); Writer.close ();

To modify the XML file steps in code:

Find the node you want to modify

1) Modify the value of the property

Attribute.setvalue ("new attribute value");

2) Modify the text

Element.settext ("new text");

3) Delete tags, properties

Element.detach ();

Attribute.detach ();

Write back to hard disk overwrite the original file

XMLWriter XMLWriter = new XMLWriter (New FileOutputStream ("XML file name. xml"));

Xmlwriter.write (DOC);

Xmlwriter.close ();

Attached:XPath: Mainly for the node object required for fast XML acquisition

1. Import dom4j jar Package and Support XPath technology jar package

2. Use the XPath method:

list<node> list = Rootelement.selectnodes ("XPath expression"); Querying multiple Node objects

Node Nade = Rootelement.selectsinglenode ("XPath expression"); Querying a Node object

3. XPath expression

/absolute Path Select the tag under the tag

Relative paths all tags under the label, representing selection elements that are not divided into any hierarchy.

* Wildcard means matching all elements

[] condition indicates which element is selected under what conditions

The @ property represents the Select Attribute node, which locates a property name

and relationships (equivalent to &&) of conditions

Not () Take counter

Text () literal indicates selection of text content

egg:string Path = "//user[@id = ' 2 ']/name"; Select the name tag under the user tag for all user tags in the id= "2"

Third, sax parsing

Sax parsing has two parts, parsers and event handlers

The parser is the XmlReader interface, responsible for reading the XML document, and sending events to the event handler (also the event source)

Event handler ContentHandler interface, responsible for responding to events sent and processing XML documents

To simplify development, the ContentHandler class DefaultHandler class is provided.

Event handlers

public class mycontenthandler extends defaulthandler{//called at the beginning of document parsing, this method will only be called once @overridepublic  void startdocument ()  throws saxexception {super.startdocument ();} Call @overridepublic void startelement at the beginning of the label (string uri, string localname, string  qname, attributes attributes)  throws saxexception { //uri:xml document namespace (not available)  //localname: The name of the tag (not available)  //qname: The name of the label with the namespace (use this with the label name)  //  Attributes: The attribute set of the label Super.startelement (uri, localname, qname, attributes);} When parsing the contents of a tag, call @overridepublic void characters (char[] ch, int start, int  Length)  throws saxexception {//ch: The byte array that is currently read to the Textnode (text node)//start: Byte start position, 0 reads all// Length: Current Textnode  super.characters (ch, start, length);} Call @overridepublic void endelement at the end of the label (string uri, string localname, string  qname)  throws saXexception {super.endelement (uri, localname, qname);} Called after the document resolves, the method will only call once @overridepublic void enddocument ()  throws saxexception { Super.enddocument ();}}

Parser

Gets the parser factory object, which gets the parser object

SAXParserFactory factory = Saxparserfactory.newinstance ();

SAXParser parser = Factory.newsaxparser ();

Resolves the specified file using the specified DefaultHandler

Parser.parse (New file ("filename. xml"), New Mycontenthandler ());

Iv. Pull Analysis

Xmlpull is more concise than sax and does not need to scan through the entire stream

Steps:

Import Kxml2-2.3.0.jar Xmlpull_1_1_3_4c.jar third-party jar packages

Gets the parser factory object, which gets the parser object xmlpullparserfactory factory = xmlpullparserfactory.newinstance (); Xmlpullparser parser = factory.newpullparser ();//Associate XML file Parser.setinput (new  FileInputStream ("filename. xml"),  "Utf-8");//Get Event Type Int type = parser.geteventtype ();// Xmlpullparser.start_document; document start event 0//xmlpullparser.end_document; Document End Event 1//xmlpullparser.start_tag;  Start tag event 2//xmlpullparser.end_tag;  end tag event 3//xmlpullparser.text; represents the text 4while  (type !=  xmlpullparser.end_document)  {string tagname = parser.getname ();switch  (type)  { Case xmlpullparser.start_tag:if ("label name". Equals (TagName)) {//action (JavaBean)}else if ("tag name". Equals (TagName)) {//...} Break;case xmlpullparser.end_tag:if ("label name". Equals (TagName)) {//operation (add)}break;} Let the pointer jump to the next line, re-assign the type, or it will die Loop Type = parser.next ()}//serialize the in-memory data to the hard disk to permanently save//Get the Parser factory object, thereby obtaining the serializer xmlpullparserfactory factory = xmlpullparserfactory.newinstance (); XmlserializEr serializer = factory.newserializer ();//Set Output stream association XML file Serializer.setoutput (new  FileOutputStream ("file name. xml"),  "Utf-8");//write document declaration (document start) serializer.startdocument ("Utf-8",  true);// Parameter two: document is independent//write start root tag serializer.starttag (null,  "Students");//Parameter 1  namespace general to null  parameter 2  tag name// Write the child label of the root tag student start tag Serializer.starttag (null,  "student"); Serializer.attribute (null,  "id",  "id value" );//write the attribute//write the child label of the student label name start tag Serializer.starttag (null,  "name");//write the text serializer.text ("text content") in the name tag; /write name end tag Serializer.endtag (null,  "name");//The same method writes student tag's sub-label age//writes student end tag Serializer.endtag (NULL,   "student");//The same method of writing multiple student, generally using the loop//write end root tag serializer.endtag (null,  "Students");// Document End Serializer.enddocument ();

XML Extensible Markup Language