This section will demonstrate a couple of ways to use the results of a Hibernate query as the datasource of a report in JasperReports.

When the Hibernate query returns a simple collection of objects, The  JRBeanCollectionDataSource class in the JasperReports library will work fine.

List cats = session.find("from eg.Cat");

Map parameters = new HashMap();
parameters.put("Title", "The Cat Report");

InputStream reportStream = this.class.getResourceAsStream("/the-cat-report.xml");
JasperDesign jasperDesign = JasperManager.loadXmlDesign(reportStream);
JasperReport jasperReport = JasperManager.compileReport(jasperDesign);

JRBeanCollectionDataSource ds = new JRBeanCollectionDataSource(cats);
JasperPrint jasperPrint = JasperManager.fillReport(jasperReport, parameters, ds);

JasperManager.printReportToPdfFile(jasperPrint, "the-cat-report.pdf");

However, when the Hibernate query returns tuples of objects (each tuple as an array, each array as an element in the returned List), things get a little tricky. Jasper needs a way to reference each object in the array by a field name. This class is a good solution, but at this time you are required to pass an array of field names matching the results of the query.

public class HibernateQueryResultDataSource implements JRDataSource { 

  private String[] fields; 
  private Iterator iterator; 
  private Object currentValue; 

  public HibernateQueryResultDataSource(List list, String[] fields) { 
    this.fields = fields; 
    this.iterator = list.iterator(); 
  } 

  public Object getFieldValue(JRField field) throws JRException { 
    Object value = null; 
    int index = getFieldIndex(field.getName()); 
    if (index > -1) { 
      Object[] values = (Object[])currentValue; 
      value = values[index]; 
    } 
    return value; 
  } 

  public boolean next() throws JRException { 
    currentValue = iterator.hasNext() ? iterator.next() : null; 
    return (currentValue != null); 
  } 

  private int getFieldIndex(String field) { 
    int index = -1; 
    for (int i = 0; i < fields.length; i++) { 
      if (fields[i].equals(field)) { 
        index = i; 
        break; 
      } 
    } 
    return index; 
  } 

}

Now running your report would look something like this:

List cats = session.find("select cat.type, cat.birthdate, cat.name from eg.DomesticCat cat");

Map parameters = new HashMap();
parameters.put("Title", "The Cat Report");

InputStream reportStream = this.class.getResourceAsStream("/the-cat-report.xml");
JasperDesign jasperDesign = JasperManager.loadXmlDesign(reportStream);
JasperReport jasperReport = JasperManager.compileReport(jasperDesign);

String[] fields = new String[] { "type", "birthdate", "name"};
HibernateQueryResultDataSource ds = new HibernateQueryResultDataSource(cats, fields);
JasperPrint jasperPrint = JasperManager.fillReport(jasperReport, parameters, ds);

JasperManager.printReportToPdfFile(jasperPrint, "the-cat-report.pdf");

Another, alternate implementation, from Erik Romson:

public class HibernateQueryResultDataSource implements JRDataSource
{
    private static final transient Logger logger = 
        Logger.Factory.getInstance(HibernateQueryResultDataSource.class);
    protected HashMap fieldsToIdxMap=new HashMap();
    protected Iterator iterator;
    protected Object currentValue;
    List values;

    public HibernateQueryResultDataSource(List list, String query)
    {
        int start =query.indexOf("select ");
        int stop =query.indexOf(" from ");
        Assertion.assertTrue(
           (start!=-1) && 
           (stop!=-1),
           "The query "+
           query+
           " must be of the form select x,x from ..."
        );
        start+="select".length();
        String parameters=query.substring(start,stop);
        parameters=parameters.trim();
        Assertion.assertTrue(
            parameters.length()>0,
            "The query "+
            query+
            " seems to be weird"
        );
        StringTokenizer tokenizer=new StringTokenizer(parameters,",");
        int idx=0;
        while( tokenizer.hasMoreTokens() )
        {
            String parameter=tokenizer.nextToken();
            fieldsToIdxMap.put( parameter.trim(), new Integer(idx) );
            idx++;
        }
        values=list;
        this.iterator = list.iterator();
    }

    public Object getFieldValue(JRField field) throws JRException
    {
        String fieldName=field.getName().replace('_','.'); 
        //JasperReports does not allow '.' in field names, so we 
        //use '_' for nested properties instead and must convert here 
        //(comment added by kbrown)
        Integer idxInt=(Integer) fieldsToIdxMap.get(fieldName);
        if (idxInt==null)
        {
            Assertion.fail(
                "The field \""+
                fieldName+
                 "\" did not have an index mapping. Should be one off "+
                fieldsToIdxMap.keySet()
            );
        }
        Object[] values = (Object[]) currentValue;
        Assertion.assertTrue(
            idxInt.intValue()<values.length,
            "The index from field "+
            fieldName+
            " was illegal"
        );
        Object value= values[ idxInt.intValue() ];
        if ( logger.isDebugEnabled() )
        {
            logger.debug("fetched value "+value+" from field "+fieldName);
        }
        return value;
    }

    public boolean next() throws JRException
    {
        currentValue = iterator.hasNext() ? iterator.next() : null;
        return currentValue != null;
    }

    public List getValues()
    {
        return values;
    }
}

Using the information from this page I've made a patch to JasperReports 0.6.5. You can find the patch at: http://www.waltermourao.com.br/JasperReports/jr65_hql.zip or you can download the full version from: http://www.waltermourao.com.br/JasperReports/jasperreports-hql-0.6.5.zip