How to parse Xml file -- Dom4j!

Dom4j is a powerful and common tool to parse the xml file.DOM(Document Object Model)

There are two main stream in parsing xml file:DOM and SAX

Let me introduce the two parts' advantage and disadvantage:

　　DOM:(W3C introduced)

　　　　1.To parse the xml , DOM should load the whole file to create dom tree.

　　　　2.When the file is too large , it's easy to cause the memory leak.

　　SAX:

　　　　1.Load the single node to trigger the event, so SAX covers little memeory

　　　　2.SAX is easy to read and unconvenient to modify the xml file.

Using dom4j is simple and clear.Important class: Node,Element,Document,Attribute

How to get the element?

For example:

　　//Get the SAXReader object

　　SAXReader reader = new SAXReader();

　　//Get the document object through SAXReader's read() method

　　Document document = reader.reade(new File(path));

　　//When the document object has been get , the RootElement should be get to find other child element

　　Element rootElement = document.getRootElement();

　　//In the Element, there is a method call element(),which will help us find the child element

　　Element childElement = rootElement.element("Student");

　　//Get the element's text content

　　String content = childElement.getTextTrim();

　　...

　　...//other element could also be get.

How to get the attribute?

　　//1.get the attribute through the attribute's index

　　Attribute att1 = element.attribute(0);

　　//2.get the attribute through the attribute's name

　　Attribute att2 = element.attribute("attribute's name");

　　//3.get all the attributes' list

　　List<Attribute> list = element.attributes();

How to get the attribute's value?

　　//1.get the attribute's value through attribute

　　String value = attribute.getValue();

　　//2.get the attribute's value from element and find the attribute by element

　　String value2 = element.attributeValue("attribute's name");

How to add the Element?

　　//1.get the root element through Document

　　Element rootElement = document.getRootElement();

　　//2.add the Element 

　　rootElement.addElement("Student").addAttribute("id","001").addElement("name").addText("zhangsan");

　　//3.and you can preread the xml file which is stored in the memory

　　String xmlText = document.asXML();

　　System.out.println("xmlText:"+xmlText);

How to remove the element and attribute?

　　Firstly, you should always remember , to remove the element,get the parentElement is required.

　　so ,the format to remove the Element is parentElement.remove(childElement);

　　//1.get the rootElement

　　Element rootElement = document.getRootElement();

　　//2.get the elements of the rootElement

　　List<Element> list = rootElement.elements();

　　//3.get the specific element

　　Element stuElement = list.get(0);

　　//4.remove the Student element by rootElement

　　rootElement.remove(stuElement);

　　//5.to check the stuElement has been removed ,we could use asXML() to tell.

　　System.out.println(document.asXML());