Java XML Overview

Java XML is simply working with an XML document from a Java program. Imagine, we have a file "products.xml" where we have product details such as name, brand and price.

Now, we want to update prices for some products using Java programming. Before writing such java programs to access XML documents, we should know basics of XML.

What is XML?

XML stands for EXtensible Markup Language. It is a text-based markup language which is used to store and transport data. It is self-descriptive and both human-readable and, machine-readable. Following are some notable points on XML −

• XML is a markup language.

• XML is a tag based language like HTML.

• XML tags are not predefined like HTML.

• You can define your own tags which is why it is called extensible language.

• XML tags are designed to be self-descriptive.

• XML is W3C Recommendation for data storage and data transfer.

XML Document

An XML document is the collection of elements that define data in a well structured and organized manner. An XML document has two sections, namely, document prolog and document elements.

Syntax

Following is the syntax of an XML document −

	
	...

Where,

• is the XML declaration statement. If included, it must be kept in the first line.
• is the root element and it is the parent of all other elements.
• is the sub element of the root element.

Example

Following example shows Employee details with as the root element and , , as sub elements. Data for each element is enclosed between opening and closing tags.

	Kiran
	developer
	25,000

Elements in XML

An element is the building block of an XML document. It consists of an opening tag, content and a closing tag. In an xml document, there should always be a root element, inside which we can write many sub elements. Elements can also have any number of attributes inside them.

Syntax

Following is the syntax of an XML element −

	
		.....
	

Where,

• is the root element of the XML document.
• is the child element and its parent is the root element.
• is the sub child and its parent is the child element.

Example

Let us see an example where DOB(date of birth) is further structured into date, month and year. Here, is the root element and , , are child elements.

	27
	March
	2000

Tags in XML

Tags in XML are self-explanatory and user defined. These are enclosed in less than (<) and greater than (>) symbols. XML is case sensitive and hence opening and closing tags should have same name.

Example

In the following example, we have written an address element with opening and closing tags.

Hyderabad

Now, let us see some incorrect ways of writing XML tags:

Since, XML is case sensitive unlike HTML, it throws the error: Opening and ending tag mismatch.

Attributes in XML

Elements in XML can have attributes. Attributes are name-value pairs that provide further specific information about a particular element. An element can have any number of attributes.

Syntax

Following is the syntax for XML attributes −

content	

Where,

• element_name is the name of the element.
• attribute_name is the name of the attribute.
• value is the value of the corresponding attribute.

Example

Now, let's look at the following example where we have four attributes, name, class, marks and DOB for the 'Student' element.

Using sub elements to replace attributes

Instead of attributes, sub elements can also be used in elements to achieve the same purpose as of attributes. The same student example can also be written as follows:

	Kiran
	8
	50
	27-03-2000

It is always a best practice to use sub elements instead of attributes. Because, sub elements can further be extended whereas attributes cannot be extended.

In the above example, If we further want the date of birth as date, month and year then it can be done by using sub elements for DOB element as follows :

	Kiran
	8
	50
	
		27
		03
		2000
	

XML Declaration

XML declaration describes the basic format information such as version, encoding and standalone status about the entire XML document. If an XML declaration is included in the document, it must be written in the first line.

By default, if declaration is not mentioned, XML parser considers the document is in version 1.0

Syntax

Following is the syntax of XML declaration −

Where,

• XML declaration starts with the character sequence and ends with the character sequence ?>
• version is the version number of the XML used
• encoding is the character encoding used for the content of XML document
• standalone is a boolean attribute whose default value is set to 'no'. This tells whether the XML document is standalone or uses information from external source to parse the document such as DTD(Document Type Definition). The default value is set to 'no'.

	
		CSE
		CS
		25
	
	
		ECE
		EC
		20
	

OvalWood315000

RectangleMarble625000

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    Rectangle
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    6
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	Oval
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	3
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    Rectangle
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    Trevi Furniture
    Engineered wood
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