Develop Reference

Can I parse XML in Java without taking XML file input from outside?

Generally using DOM, SAX or XPath etc parser we do take input from outside Java code like this:
File inputFile = new File("C:\\Users\\DELL\\Desktop\\catalog.xml");
DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse(inputFile);
So can you parse XML file without taking input like this? I want to write my XML code alongside Java code.

Use DocumentBuilder.parse(new InputStream(new StringReader(xml))) where xml is a string containing the XML to be parsed.
That's if you really must use DOM. I can't imagine why anyone uses it any more, when alternatives such as JDOM2 are so much better.

which is the best way for fetching value from XML : JAXB or DOM?

Which one is the efficient way for reading xml. I'm aware of two ways:
1)JAXB:
By annotating my classes with jaxb annotation we get the xml in java object vice versa using Marshalling & Unmarshalling of object.
2)DOM:
Using dom parser for parsing the xml and using xpath values from xml can be accessed.
Example of DOM:
File fXmlFile = new File("/Users/link1/input.xml");
DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse(fXmlFile);
doc.getDocumentElement().normalize();
As per the business demands, I'm expecting to use the fastest way and the better way between the above two. Suggestions and few tactics would be appreciated.

First question to ask: does your XML always have the same structure and can this structure be mapped on a hierarchy of Java objects?
If Yes -> either use JAXB or Jackson XmlMapper
If No (the structure of your XML varies) -> Do you require random access to the data in your XML with many reads and possibly some writes (after which you convert the data back to XML)?
2.1. If Yes -> use DOM (It is designed for in memory handling of the XML Document Tree, but has more overhead)
2.2. If No (more efficient XML parsing) -> Do you need to parse all information in the XML or do you need XML validation?
2.2.1 If Yes -> use SAX (it is included in the JDK and allows for validation)
2.2.2 If No -> use StAX (it is an XML pull parser that allows reading some values in the XML without having to parse the full XML, but it does not offer validation.)

SAXParseException when “ is used in XML

I'm getting a "org.xml.sax.SAXParseException; lineNumber: 4; columnNumber: 26; The entity "ldquo" was referenced, but not declared." exception when reading an XML document. I'm reading it as follows:
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
InputSource is = new InputSource(new StringReader(xmlBody));
Document document = builder.parse(is);
And then there's an exception on builder.parse(is);
From searching I figured that it is necessary to declare some of those new entities externally, unfortunately, I cannot modify the original XML document.
How do I fix this problem?
Thanks

From searching I figured that it is necessary to declare some of those new entities externally, unfortunately, I cannot modify the original XML document.
Well, unless you declare the entity then the document isn't XML and you won't be able to process it using an XML parser.
When you are asked to process input that isn't well-formed XML, the best approach is to fix the process that created the document (the whole idea of using XML for interchange relies on it being well-formed XML). The alternatives are to "repair" the document to turn it into well-formed XML (which you say you can't do), or to forget the fact that it was intended to be XML, and treat it as you would any proprietary non-XML format.
Not a pleasant set of choices - but that's the mess you get into when people pay lip-service to XML but fail to conform to the letter of the standard.

Try
factory.setExpandEntityReferences(false);
This will prevent the parser from trying to expand entities.
EDIT: How about this http://xerces.apache.org/xerces2-j/features.html#dom.create-entity-ref-nodes -- The top of that page has an example of how to set features on the underlying parser. This should cause the parser to create entity-reference DOM nodes instead of trying to expand the entities.

Java XML parser?

I'm currently converting a program I wrote in Visual Basic .NET (the 2005 variety) into Java. It used built-in XML methods to parse and generate the user's saved data, does Java have an equivalent feature built in or am I going to have to change file processing implementations? (I'd rather not, there's a lot of code I'd have to change.)

Yes, Java can parse XML. Here's an example that takes in a String that contains XML and builds a Document object out of it:
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
InputSource inputSource = new InputSource(new StringReader(xml));
Document document = documentBuilder.parse(inputSource);
You can then use the XPath API to query the dom. Here's a tutorial/writeup about it.
As far as serializing objects to XML, the official implementation is JAXB and it is part of Java since 1.6. Here's a simple example. It will let you serialize and deserialize to and from XML.
You can also create a DOM object manually and add nodes to it, but it's a little more tedious:
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();
Document document = documentBuilder.newDocument();
Element rootNode = document.createElement("root");
Element childNode = document.createElement("child");
childNode.setTextContent("I am a child node");
childNode.setAttribute("attr", "value");
rootNode.appendChild(childNode);
document.appendChild(rootNode);

I'm assuming that you mean that the properties/structure was generated through the classes/beans themselves? If so, then the answer is no [without an third party component]. I've used XStream before, and that is about the closest that I've gotten to .NET's XML Class serialization.

Querying an HTML page with XPath in Java

Can anyone advise me a library for Java that allows me to perform an XPath Query over an html page?
I tried using JAXP but it keeps giving me a strange error that I cannot seem to fix (thread "main" java.io.IOException: Server returned HTTP response code: 503 for URL: http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd).
Thank you very much.
EDIT
I found this:
// Create a new SAX Parser factory
SAXParserFactory factory = SAXParserFactory.newInstance();
// Turn on validation
factory.setValidating(true);
// Create a validating SAX parser instance
SAXParser parser = factory.newSAXParser();
// Create a new DOM Document Builder factory
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
// Turn on validation
factory.setValidating(true);
// Create a validating DOM parser
DocumentBuilder builder = factory.newDocumentBuilder();
from http://www.ibm.com/developerworks/xml/library/x-jaxpval.html But turning the argumrent to false did not change anything.

Setting the parser to "non validating" just turns off validation; it does not inhibit fetching of DTD's. Fetching of DTD is needed not just for validation, but also for entity expansion... as far as I recall.
If you want to suppress fetching of DTD's, you need to register a proper EntityResolver to the DocumentBuilderFactory or DocumentBuilder. Implement the EntityResolver's resolveEntity method to always return an empty string.

Take a look at this:
http://www.w3.org/2005/06/blog/systeam/2008/02/08/w3c_s_excessive_dtd_traffic
Probably you have the parser set to perform DOM validation, and it is trying to retrieve the DTD. JAXP should have a way to disable DTD validation, and just run XPATH against a document assumed to be valid. I haven't used JAXP is many years so I'm sorry I couldn't be more helpful.