How to parse an XML file with DTD validation using the DOM API?

if you want to parse an XML file with DTD validation using the DOM API, you can follow these suggestions:

1. Set the validation flag to true on DocumentBuilderFactory object:

      DocumentBuilderFactory f = DocumentBuilderFactory.newInstance();
    f.setValidating(Boolean.parseBoolean(args[1]));
      DocumentBuilder b = f.newDocumentBuilder();

2. Provide the XML file with DTD included, UserError.xml:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<!-- Copyright (c) 2017 FYIcenter.com -->
<!DOCTYPE User [
   <!ELEMENT User (ID+, BirthDate+, Name+, Sex+)>
   <!ELEMENT ID (#PCDATA)>
   <!ELEMENT BirthDate (#PCDATA)>
   <!ELEMENT Name (#PCDATA)>
   <!ELEMENT Sex (#PCDATA)>
]>

<User>
    <ID>101</ID>
    <Name>Frank Y. Ivy</Name>
</User>

Here is a complete example of parsing an XML with DTD validation using SAX API, SaxXmlDtdValidation.java:

// Copyright (c) 2017 FYIcenter.com
import java.io.*;
import javax.xml.parsers.*;
import org.w3c.dom.*;

public class DomXmlDtdValidation {
   static String dot = "............................................................";
   public static void main(String[] args) throws Exception {
      DocumentBuilderFactory f = DocumentBuilderFactory.newInstance();
    f.setValidating(Boolean.parseBoolean(args[1]));
      DocumentBuilder b = f.newDocumentBuilder();
      Document d = b.parse(new File(args[0]));
      System.out.println("Implementation class:\n   "+d.getClass().getName());

      System.out.println("DOM object elements and text contents:");
    Node n = d.getDocumentElement();
    printText(n, 1);
   }
   public static void printText(Node n, int l) {
      String v = "";
      if (n.getNodeType()==Node.TEXT_NODE) v = n.getTextContent();
      System.out.println(dot.substring(0,l)+n.getNodeName()+":"+v);
    NodeList c = n.getChildNodes();
    for (int i=0; i<c.getLength(); i++) {
       printText(c.item(i),l+1);
    }
   }
}

Compile and run the example program, DomXmlSerializer.java:

>\fyicenter\jdk-1.8.0\bin\javac DomXmlDtdValidation.java

>\fyicenter\jdk-1.8.0\bin\java DomXmlDtdValidation UserError.xml true

Warning: validation was turned on but an org.xml.sax.ErrorHandler was not set, w
hich is probably not what is desired.  Parser will use a default ErrorHandler to
 print the first 0  errors.  Please call the setErrorHandler method to fix this.

Error: URI=file:UserError.xml
Line=14: The content of element type "User" must match "(ID+,BirthDate+,Name+,Sex+)".

Implementation class:
   com.sun.org.apache.xerces.internal.dom.DeferredDocumentImpl
DOM object elements and text contents:
.User:
..#text:

..ID:
...#text:101
..#text:

..Name:
...#text:Frank Y. Ivy
..#text:

If you run it again with "false", you will not see any validation errors:

>\fyicenter\jdk-1.8.0\bin\java DomXmlDtdValidation UserError.xml false

Implementation class:
   com.sun.org.apache.xerces.internal.dom.DeferredDocumentImpl
DOM object elements and text contents:
.User:
..#text:

..ID:
...#text:101
..#text:

..Name:
...#text:Frank Y. Ivy
..#text:

⇒ DomXmlXsValidation.java - DOM Parser with XS Validation

⇐ DomXmlSerializer.java - Serialize DOM to XML String

⇑ Using XML DOM API with Apache Xerces

⇑⇑ FAQ for Apache Xerces XML Parser