I am trying to build server that sends a xml file to client. I am getting info from db and wants to build from that xml file.
But I have a problem with:
DocumentBuilder documentBuilder = null;
Document doc =documentBuilder.newDocument();
I am getting NullPointerException. Here is me full code:
public void createXmlTree() throws Exception {
//This method creates an element node
DocumentBuilder documentBuilder = null;
Document doc =documentBuilder.newDocument();
Element root = doc.createElement("items");
//adding a node after the last child node of the specified node.
doc.appendChild(root);
for(int i=0;i<db.stories.size();i++){
Element child = doc.createElement("item");
root.appendChild(child);
Element child1 = doc.createElement("title");
child.appendChild(child1);
Text text = doc.createTextNode(db.stories.get(i).title);
child1.appendChild(text);
//Comment comment = doc.createComment("Employee in roseindia");
//child.appendChild(comment);
Element child2 = doc.createElement("date");
child.appendChild(child2);
Text text2 = doc.createTextNode(db.stories.get(i).date);
child2.appendChild(text2);
Element child3 = doc.createElement("text");
child.appendChild(child3);
Text text3 = doc.createTextNode(db.stories.get(i).text);
child3.appendChild(text3);
root.appendChild(child3);
Well yes, you would get a NullPointerException. You're calling a method on a null reference - very clearly, given that you've assigned the documentBuilder a null value on the line before. You need to get an instance of DocumentBuilder to start with. For example:
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder documentBuilder = factory.newDocumentBuilder();
of course you are getting a NullPointerException, your DocumentBuilder is null.
Try instantiating it first.
// Step 1: create a DocumentBuilderFactory
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
// Step 2: create a DocumentBuilder
DocumentBuilder db = dbf.newDocumentBuilder();
Guys are right about DocumentBuilder. But may I offer you other solution? Your servlet mostly deals with generating of XML itself, i.e. produces kind of markup. This is the purpose of JSP. You can implement simple JSP page that will actually contain template of your XML and some code that inserts dynamic data. This is much simpler and easier to maintain.
Yes, JSP typically generate HTML but no-one said that they cannot generate XML or any other text format. Just do not forget to set content type to text/xml.
Do you really need to write you XML manually?
Do you have the XSD of the XML you want to write?
Because, it would be easier to generate some classes using XJC/JAXB and use the marshaller to write your XML file.
Related
first of all please excuse my shallow understanding into coding as I am a business analyst. Now my question. I am writing java code to convert a csv into xml. I am able to read csv successfully into objects. However, while writing the xml, when special a space or "=" is encounteredan error is thrown.
Piece of the problematic code, I have imporovised the value in create element just to highlight the problem. In actual I am getting this value from an object:-
DocumentBuilderFactory documentFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder documentBuilder = documentFactory.newDocumentBuilder();
Document xmlDocument= documentBuilder.newDocument();
Element root = xmlDocument.createElement("Media NationalGroupId="8" AllFTA="1002" AllSTV="1001");
xmlDocument.appendChild(root);
My xml should look something like this
<Media DateCreated="20200224 145251" NationalGroupId="8" AllFTA="1002" AllSTV="1001" AllTV="1000" NextId="1000000">
createElement should only receive Media as the argument.
To add the other attributes (DateCreated, NationalGroupId, etc), you need to call setAttribute on root, one by one.
In my program i have to create some document creator and I want to split functionality of creating elements into several classes. Each class will create a single element and main creator will extract that element via interface and attach to body.
The thing is that i don't want to pass any arguments into constructors call e.g.
creator.createDocument()
.setDocumentHeader(
new DocumentHeader()
.setSomeValue(41)
)
To simplify the problem lets say that I have a code
import org.w3c.dom.Document;
import org.w3c.dom.Element;
DocumentBuilderFactory dbfac1 = DocumentBuilderFactory.newInstance();
DocumentBuilder docBuilder1 = dbfac1.newDocumentBuilder();
Document document1 = docBuilder1.newDocument();
DocumentBuilderFactory dbfac2 = DocumentBuilderFactory.newInstance();
DocumentBuilder docBuilder2 = dbfac2.newDocumentBuilder();
Document document2 = docBuilder2.newDocument();
Element elementFromDoc1 = document1.createElement("body");
Element elementFromDoc2 = document2.createElement("someElement");
The question is, is that legal to do the following operation?
elementFromDoc1.appendChild(elementFromDoc2);
The code you have will throw an exception about the element being from a different document.
However, you can use document1.importNode I think. Here is the documentation:
http://docs.oracle.com/javase/7/docs/api/org/w3c/dom/Document.html#importNode(org.w3c.dom.Node,%20boolean)
And here is an example from another question:
Java appending XML docs to existing docs
I have a Node from one Document. I want to take that Node and turn it into the root node of a new Document.
Only way I can think of is the following:
Node node = someChildNodeFromDifferentDocument;
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true);
DocumentBuilder builder = factory.newDocumentBuilder();
Document newDocument = builder.newDocument();
newDocument.importNode(node);
newDocument.appendChild(node);
This works, but I feel it is rather annoyingly verbose. Is there a less verbose/more direct way I'm not seeing, or do I just have to do it this way?
The code did not work for me - but with some changes from this related question I could get it to work as follows:
Node node = someChildNodeFromDifferentDocument;
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true);
DocumentBuilder builder = factory.newDocumentBuilder();
Document newDocument = builder.newDocument();
Node importedNode = newDocument.importNode(node, true);
newDocument.appendChild(importedNode);
That looks about right to me. While it does look generally verbose, it certainly doesn't look significantly more verbose than other code using the DOM API. It's just an annoying API, unfortunately.
Of course, it's simpler if you've already got a DocumentBuilder from elsewhere - that would get rid of quite a lot of your code.
document from Node
Document document = node.getOwnerDocument();
Maybe you can use this code:
String xmlResult = XMLHelper.nodeToXMLString(node);
Document docDataItem = DOMHelper.stringToDOM(xmlResult);
You can simply clone the old document using cloneNode and then typecast it to Document like below:
Document newDocument = (Document) node.cloneNode(true);
I'm building an android app that communicates to a web server and am struggling with the following scenario:
Given ONE line of XML in a String eg:
"<test one="1" two="2" />"
I would like to extract the values into a HashMap so that:
map.get("one") = "1"
map.get("two") = "2"
I already can do this with a full XML document using the SAX Parser, this complains when i try to just give it the above string with a MalformedUrlException: Protocol not found
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder;
Document doc = null;
builder = factory.newDocumentBuilder();
doc = builder.parse("<test one="1" two="2" />"); //here
I realize some regex could do this but Id really rather do it properly.
The same behaviour can be found at http://metacpan.org/pod/XML::Simple#XMLin which is what the web server uses.
Can anyone help? Thanks :D
DocumentBuilder.parse(String) treats the string as a URL. Try this instead:
Document doc = builder.parse(new InputSource(new StringReader(text)));
(where text contains the XML, of course).
I've spent a while looking around on Google for a way to convert a org.w3c.dom.Document to a string representation of the whole DOM tree, so I can save the object to file system.
However all the solutions I've found use javax.xml.transform.Transformer which isn't supported as part of the Android 2.1 API. How can I do this without using this class/containing package?
Please try this code:
DocumentBuilderFactory docFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder docBuilder = docFactory.newDocumentBuilder();
Document doc = docBuilder.parse("/path/to/file.xml");
DOMImplementation domImpl = ownerDocument.getImplementation();
DOMImplementationLS domImplLS = (DOMImplementationLS)domImpl.getFeature("LS", "3.0");
LSSerializer serializer = domImplLS.createLSSerializer();
serializer.getDomConfig().setParameter("xml-declaration", Boolean.valueOf(false));
LSOutput lsOutput = domImplLS.createLSOutput();
lsOutput.setCharacterStream(output);
serializer.write(doc, lsOutput);
To avoid using Transformer you should manually iterate over your xml tree, otherwise you can rely on some external libraries. You should take a look here.