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12.18. Implementing a Source Reader for use with Smooks

  1. You should first implement a basic reader class as shown below: 
     public class MyCSVReader implements SmooksXMLReader 
{
   // Implement all of the XMLReader methods...
}
    Two methods from the org.xml.sax.XMLReader interface are of particular interest:
    1. setContentHandler(ContentHandler) is called by Smooks Core. It sets the org.xml.sax.ContentHandler instance for the reader. The org.xml.sax.ContentHandler instance methods are called from inside the parse(InputSource) method.
    2. parse(InputSource) : This is the method that receives the Source data input stream, parses it (i.e. in the case of this example, the CSV stream) and generates the SAX event stream through calls to the org.xml.sax.ContentHandler instance supplied in the setContentHandler(ContentHandler) method.
    Refer to http://download.oracle.com/javase/6/docs/api/org/xml/sax/ContentHandler.html for more details.
  2. Configure your CSV reader with the names of the fields associated with the CSV records. Configuring a custom reader implementation is the same for any Smooks component. See the example below: 
    public class MyCSVReader implements SmooksXMLReader 
{

    private ContentHandler contentHandler;

    @ConfigParam
    private String[] fields; // Auto decoded and injected from the "fields" <param> on the reader config.

    public void setContentHandler(ContentHandler contentHandler) {
        this.contentHandler = contentHandler;
    }

    public void parse(InputSource csvInputSource) throws IOException, SAXException {
        // TODO: Implement parsing of CSV Stream...
    }

    // Other XMLReader methods...
}
  3. Now that you have the basic Reader implementation stub, you can start writing unit tests to test the new reader implementation. To do this you will need something with CSV input. Observe the example below featuring a simple list of names in a file with the name names.csv: 
    Tom,Jones
Mike,Jones
Mark,Jones
  4. Use a test Smooks configuration to configure Smooks with your MyCSVReader. As stated before, everything in Smooks is a resource and can be configured with the basic <resource-config> configuration. While this works fine, it's a little noisy, so Smooks provides a basic <reader> configuration element specifically for the purpose of configuring a reader. The configuration for the test looks like the following, in the mycsvread-config.xml: 
    <smooks-resource-list xmlns="http://www.milyn.org/xsd/smooks-1.1.xsd">
   <reader class="com.acme.MyCSVReader">
      <params>
         <param name="fields">firstname,lastname</param>
      </params>
   </reader>
</smooks-resource-list>
  5. Implement the JUnit test class: 
    public class MyCSVReaderTest extends TestCase 
{
    
    public void test() {
        Smooks smooks = new Smooks(getClass().getResourceAsStream("mycsvread-config.xml"));
        StringResult serializedCSVEvents = new StringResult();

        smooks.filterSource(new StreamSource(getClass().getResourceAsStream("names.csv")), serializedCSVEvents);

        System.out.println(serializedCSVEvents);

        // TODO: add assertions etc
    }
}
  6. Implement the parse method: 
    public class MyCSVReader implements SmooksXMLReader 
{
    private ContentHandler contentHandler;

    @ConfigParam
    private String[] fields; // Auto decoded and injected from the "fields" <param> on the reader config.

    public void setContentHandler(ContentHandler contentHandler) 
    {
        this.contentHandler = contentHandler;
    }

    public void parse(InputSource csvInputSource) throws IOException, SAXException 
    {
        BufferedReader csvRecordReader = new BufferedReader(csvInputSource.getCharacterStream());
        String csvRecord;

        // Send the start of message events to the handler...
        contentHandler.startDocument();
        contentHandler.startElement(XMLConstants.NULL_NS_URI, "message-root", "", new AttributesImpl());

        csvRecord = csvRecordReader.readLine();
        while(csvRecord != null) 
        {
            String[] fieldValues = csvRecord.split(",");
        
            // perform checks...

            // Send the events for this record...
            contentHandler.startElement(XMLConstants.NULL_NS_URI, "record", "", new AttributesImpl());
            for(int i = 0; i < fields.length; i++) 
            {
                contentHandler.startElement(XMLConstants.NULL_NS_URI, fields[i], "", new AttributesImpl());
                contentHandler.characters(fieldValues[i].toCharArray(), 0, fieldValues[i].length());
                contentHandler.endElement(XMLConstants.NULL_NS_URI, fields[i], "");            
            }
            contentHandler.endElement(XMLConstants.NULL_NS_URI, "record", "");            

            csvRecord = csvRecordReader.readLine();    
        }

        // Send the end of message events to the handler...
        contentHandler.endElement(XMLConstants.NULL_NS_URI, "message-root", "");
        contentHandler.endDocument();
    }

    // Other XMLReader methods...
}
  7. Run the unit test class to see the following output on the console (formatted): 
    <message-root>
    <record>
        <firstname>Tom</firstname>
        <lastname>Jones</lastname>
    </record>
    <record>
        <firstname>Mike</firstname>
        <lastname>Jones</lastname>
    </record>
    <record>
        <firstname>Mark</firstname>
        <lastname>Jones</lastname>
    </record>
</message-root>
    After this, it is a case of expanding the tests, hardening the reader implementation code, and so on. Then you can use your reader to perform all sorts of operations supported by Smooks.