How to read and write XML files?

Question

I have to read and write to and from an XML file. What is the easiest way to read and write XML files using Java?

Answer 1

Here is a quick DOM example that shows how to read and write a simple xml file with its dtd:

<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE roles SYSTEM "roles.dtd"> <roles>     <role1>User</role1>     <role2>Author</role2>     <role3>Admin</role3>     <role4/> </roles> 

and the dtd:

<?xml version="1.0" encoding="UTF-8"?> <!ELEMENT roles (role1,role2,role3,role4)> <!ELEMENT role1 (#PCDATA)> <!ELEMENT role2 (#PCDATA)> <!ELEMENT role3 (#PCDATA)> <!ELEMENT role4 (#PCDATA)> 

First import these:

import javax.xml.parsers.*; import javax.xml.transform.*; import javax.xml.transform.dom.*; import javax.xml.transform.stream.*; import org.xml.sax.*; import org.w3c.dom.*; 

Here are a few variables you will need:

private String role1 = null; private String role2 = null; private String role3 = null; private String role4 = null; private ArrayList<String> rolev; 

Here is a reader (String xml is the name of your xml file):

public boolean readXML(String xml) {         rolev = new ArrayList<String>();         Document dom;         // Make an  instance of the DocumentBuilderFactory         DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();         try {             // use the factory to take an instance of the document builder             DocumentBuilder db = dbf.newDocumentBuilder();             // parse using the builder to get the DOM mapping of the                 // XML file             dom = db.parse(xml);              Element doc = dom.getDocumentElement();              role1 = getTextValue(role1, doc, "role1");             if (role1 != null) {                 if (!role1.isEmpty())                     rolev.add(role1);             }             role2 = getTextValue(role2, doc, "role2");             if (role2 != null) {                 if (!role2.isEmpty())                     rolev.add(role2);             }             role3 = getTextValue(role3, doc, "role3");             if (role3 != null) {                 if (!role3.isEmpty())                     rolev.add(role3);             }             role4 = getTextValue(role4, doc, "role4");             if ( role4 != null) {                 if (!role4.isEmpty())                     rolev.add(role4);             }             return true;          } catch (ParserConfigurationException pce) {             System.out.println(pce.getMessage());         } catch (SAXException se) {             System.out.println(se.getMessage());         } catch (IOException ioe) {             System.err.println(ioe.getMessage());         }          return false;     } 

And here a writer:

public void saveToXML(String xml) {     Document dom;     Element e = null;      // instance of a DocumentBuilderFactory     DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();     try {         // use factory to get an instance of document builder         DocumentBuilder db = dbf.newDocumentBuilder();         // create instance of DOM         dom = db.newDocument();          // create the root element         Element rootEle = dom.createElement("roles");          // create data elements and place them under root         e = dom.createElement("role1");         e.appendChild(dom.createTextNode(role1));         rootEle.appendChild(e);          e = dom.createElement("role2");         e.appendChild(dom.createTextNode(role2));         rootEle.appendChild(e);          e = dom.createElement("role3");         e.appendChild(dom.createTextNode(role3));         rootEle.appendChild(e);          e = dom.createElement("role4");         e.appendChild(dom.createTextNode(role4));         rootEle.appendChild(e);          dom.appendChild(rootEle);          try {             Transformer tr = TransformerFactory.newInstance().newTransformer();             tr.setOutputProperty(OutputKeys.INDENT, "yes");             tr.setOutputProperty(OutputKeys.METHOD, "xml");             tr.setOutputProperty(OutputKeys.ENCODING, "UTF-8");             tr.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, "roles.dtd");             tr.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "4");              // send DOM to file             tr.transform(new DOMSource(dom),                                   new StreamResult(new FileOutputStream(xml)));          } catch (TransformerException te) {             System.out.println(te.getMessage());         } catch (IOException ioe) {             System.out.println(ioe.getMessage());         }     } catch (ParserConfigurationException pce) {         System.out.println("UsersXML: Error trying to instantiate DocumentBuilder " + pce);     } } 

getTextValue is here:

private String getTextValue(String def, Element doc, String tag) {     String value = def;     NodeList nl;     nl = doc.getElementsByTagName(tag);     if (nl.getLength() > 0 && nl.item(0).hasChildNodes()) {         value = nl.item(0).getFirstChild().getNodeValue();     }     return value; } 

Add a few accessors and mutators and you are done!