Validator (xsd) for xml in android

Question

I have a project with API 10 (2.3.3 version) in Android and i have a problem for the validation of xml with xsd file. This is my code:

public static Document buildDoc(String xml, String xsd){
     // parse an XML document into a DOM tree
    Document document = null;

   try {            

       DocumentBuilderFactory parserFactory = DocumentBuilderFactory.newInstance();
        parserFactory.setNamespaceAware(true);
        DocumentBuilder parserdb = parserFactory.newDocumentBuilder();
        doc = parserdb.parse(new InputSource( new StringReader(xml)  ));

       SchemaFactory factory = SchemaFactory.newInstance(
                      XMLConstants.W3C_XML_SCHEMA_NS_URI);     //here the emulator raises an exception


        Source schemaFile = new StreamSource(new File(xsd));
        Schema schema = factory.newSchema(schemaFile);


        Validator validator = schema.newValidator();

        // validate the DOM tree
        validator.validate(new DOMSource(doc));
        System.out.println("Validation OK!");
    } catch (SAXException e) {
        // instance document is invalid!
             System.err.println("Validation ERROR!");
            e.printStackTrace();

    } catch (ParserConfigurationException e) {
                    // TODO Auto-generated catch block
             System.err.println("Validation ERROR!");
                    e.printStackTrace();
    } catch (IllegalArgumentException e) {
                    // TODO Auto-generated catch block
             System.err.println("Validation ERROR!");              
            } catch (IOException e) {
                    // TODO Auto-generated catch block
                     System.err.println("Validation ERROR!");
                    e.printStackTrace();

            }

    return doc;

}

My Eclipse Simulator throw an exception: E/AndroidRuntime(4770): Caused by: java.lang.IllegalArgumentException: http://www.w3.org/2001/XMLSchema

In this line: SchemaFactory factory = SchemaFactory.newInstance( XMLConstants.W3C_XML_SCHEMA_NS_URI);

Why??

Answer 1

If your question was more than just why? and more of a how can I do this... then the following may be an alternative that you might like.

I found I was not able to get the regular xerces to work with Android, however I did find Xerces-for-Android, which I got working. The following are details of the setup and some example code. Good luck :)

The following worked for me:

1. Create a validation utility.
2. Get both the xml and xsd into file on the android OS and use the validation utility against it.
3. Use Xerces-For-Android to do the validation.

Android does support some packages which we can use, I created my xml validation utility based on: http://docs.oracle.com/javase/1.5.0/docs/api/javax/xml/validation/package-summary.html

My initial sandbox testing was pretty smooth with java, then I tried to port it over to Dalvik and found that my code did not work. Some things just aren't supported the same with Dalvik, so I made some modifications.

I found a reference to xerces for android, so I modified my sandbox test of (the following doesn't work with android, the example after this does):

import java.io.File;

import javax.xml.XMLConstants;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.Source;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamSource;
import javax.xml.validation.Schema;
import javax.xml.validation.SchemaFactory;
import javax.xml.validation.Validator;

import org.w3c.dom.Document;

/**
 * A Utility to help with xml communication validation.
 */
public class XmlUtil {

    /**
     * Validation method. 
     * Base code/example from: http://docs.oracle.com/javase/1.5.0/docs/api/javax/xml/validation/package-summary.html
     * 
     * @param xmlFilePath The xml file we are trying to validate.
     * @param xmlSchemaFilePath The schema file we are using for the validation. This method assumes the schema file is valid.
     * @return True if valid, false if not valid or bad parse. 
     */
    public static boolean validate(String xmlFilePath, String xmlSchemaFilePath) {

        // parse an XML document into a DOM tree
        DocumentBuilder parser = null;
        Document document;

        // Try the validation, we assume that if there are any issues with the validation
        // process that the input is invalid.
        try {
            // validate the DOM tree
            parser = DocumentBuilderFactory.newInstance().newDocumentBuilder();
            document = parser.parse(new File(xmlFilePath));

            // create a SchemaFactory capable of understanding WXS schemas
            SchemaFactory factory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);

            // load a WXS schema, represented by a Schema instance
            Source schemaFile = new StreamSource(new File(xmlSchemaFilePath));
            Schema schema = factory.newSchema(schemaFile);

            // create a Validator instance, which can be used to validate an instance document
            Validator validator = schema.newValidator();
            validator.validate(new DOMSource(document));
        } catch (Exception e) {
            // Catches: SAXException, ParserConfigurationException, and IOException.
            return false;
        }     

        return true;
    }
}

The above code had to be modified some to work with xerces for android (http://gc.codehum.com/p/xerces-for-android/). You need SVN to get the project, the following are some crib notes:

download xerces-for-android
    download silk svn (for windows users) from http://www.sliksvn.com/en/download
        install silk svn (I did complete install)
        Once the install is complete, you should have svn in your system path.
        Test by typing "svn" from the command line.
        I went to my desktop then downloaded the xerces project by:
            svn checkout http://xerces-for-android.googlecode.com/svn/trunk/ xerces-for-android-read-only
        You should then have a new folder on your desktop called xerces-for-android-read-only

With the above jar (Eventually I'll make it into a jar, just copied it directly into my source for quick testing. If you wish to do the same, you can making the jar quickly with Ant (http://ant.apache.org/manual/using.html)), I was able to get the following to work for my xml validation:

import java.io.File;
import java.io.IOException;

import mf.javax.xml.transform.Source;
import mf.javax.xml.transform.stream.StreamSource;
import mf.javax.xml.validation.Schema;
import mf.javax.xml.validation.SchemaFactory;
import mf.javax.xml.validation.Validator;
import mf.org.apache.xerces.jaxp.validation.XMLSchemaFactory;

import org.xml.sax.SAXException;

/**
 * A Utility to help with xml communication validation.
 */public class XmlUtil {

    /**
     * Validation method. 
     * 
     * @param xmlFilePath The xml file we are trying to validate.
     * @param xmlSchemaFilePath The schema file we are using for the validation. This method assumes the schema file is valid.
     * @return True if valid, false if not valid or bad parse or exception/error during parse. 
     */
    public static boolean validate(String xmlFilePath, String xmlSchemaFilePath) {

        // Try the validation, we assume that if there are any issues with the validation
        // process that the input is invalid.
        try {
            SchemaFactory  factory = new XMLSchemaFactory();
            Source schemaFile = new StreamSource(new File(xmlSchemaFilePath));
            Source xmlSource = new StreamSource(new File(xmlFilePath));
            Schema schema = factory.newSchema(schemaFile);
            Validator validator = schema.newValidator();
            validator.validate(xmlSource);
        } catch (SAXException e) {
            return false;
        } catch (IOException e) {
            return false;
        } catch (Exception e) {
            // Catches everything beyond: SAXException, and IOException.
            e.printStackTrace();
            return false;
        } catch (Error e) {
            // Needed this for debugging when I was having issues with my 1st set of code.
            e.printStackTrace();
            return false;
        }

        return true;
    }
}

Some Side Notes:

For creating the files, I made a simple file utility to write string to files:

public static void createFileFromString(String fileText, String fileName) {
    try {
        File file = new File(fileName);
        BufferedWriter output = new BufferedWriter(new FileWriter(file));
        output.write(fileText);
        output.close();
    } catch ( IOException e ) {
       e.printStackTrace();
    }
}

I also needed to write to an area that I had access to, so I made use of:

String path = this.getActivity().getPackageManager().getPackageInfo(getPackageName(), 0).applicationInfo.dataDir;   

A little hackish, it works. I'm sure there is a more succinct way of doing this, however I figured I'd share my success, as there weren't any good examples that I found.

Answer 2

Because XML Schema isn't supported on your platform.