Kenan Sevindik

It is possible to pass data to JasperReports templates via a custom data source, which implements JRDataSource interface. Reporting engine iterates over report data collection with boolean next() method, and evaluates field expressions by asking value for them from the data source instance with calling Object getFieldValue(JRField) method. One most probably implements custom data sources as returning some property value of current data record corresponding to some field name passed from the template via reporting engine.

We have developed a concrete JRDataSource class, which takes a list as record data collection in its constructor, and then returns field values, extracting them via reflection from current record data in the collection, if there is a one to one correspondence between that record?s properties and field expressions in report template. There is no restriction in the depth of object structure while extracting field values. For example, we may have an object named A as current record data, but may ask a field value, which corresponds to some property of object named B, which is also a property of previous object named A. The sole requirement for this idiom to get work is implementing getter methods for those properties mentioned above.

There is a simple usage scenario below. Let say, we have two classes Foo and Bar as follows;

public class Foo {
    private float f;
    private Bar bar;
    public Bar getBar() {
        return bar;
    }

    public float getF() {
        return f;
    }
    ...
}

public class Bar {
    private int i;
    private String str;
    public int getI() {
        return i;
    }

    public String getStr() {
        return str;
    }
    ...
}

Later, we can define field expressions, such as, assuming an istance of class Foo is top level report data record, bar.str, bar.i, f, and access them with $F{bar.str}, $F{bar.i}, ${f} expressions respectively inside report templates.

Here is the source code of this custom data source idiom;

public class ListJRDataSource implements JRDataSource {
    private Iterator iterator;
    private Object currentObject;
    public ListJRDataSource(List objectList) {
        iterator = objectList.iterator();
    }

    public boolean next() throws JRException {
        if(iterator.hasNext()) {
            currentObject = iterator.next();
            return true;
        } else {
            return false;
        }
    }

    public Object getFieldValue(JRField jrField) throws JRException {
        String fieldName = jrField.getName();
        return FieldValueGetter.getValue(currentObject,fieldName);
    }
}

public class FieldValueGetter {
    public static Object getValue(Object target, String property) {
        int index = property.indexOf(".");
        if(index != -1) {
            target = getFieldValue(target,property.substring(0,index));
            return target != null?getValue(target,property.substring(index + 1)):null;
        } else {
            return target != null?getFieldValue(target,property):null;
        }
    }

    private static Object getFieldValue(Object target, String property) {
        try {
            property = convertToGetter(property);
            Method method = target.getClass().getMethod(property,null);
            return method.invoke(target,null);
        } catch (Exception e) {
            throw new FieldValueAccessException(e.getMessage(),e);
        }
    }

    private static String convertToGetter(String property) {
        StringBuffer buf = new StringBuffer();
        buf.append("get");
        buf.append(property.substring(0,1).toUpperCase(Locale.US));
        buf.append(property.substring(1));
        return buf.toString();
    }
}