How to access data from a java.util.List in a JavaBean using JRBeanCollectionDataSource

This guide explains how to display data stored in a List property of a JavaBean using JRBeanCollectionDataSource in your reports.

The Problem:

Consider a JavaBean with a property that holds a java.util.List of values. How can we extract and display this list's data within the Detail band of a report?

The Solution:

To accomplish this, we can leverage two key techniques:

1. Using the _THIS Expression:
Within the field expression, utilize the _THIS expression to access the current instance of the JavaBean. This allows you to extract the java.util.List property from the bean.

2. List Component in the Detail Band:
Employ a List component in the Detail band. Bind its DataSourceExpression to a new JRBeanCollectionDataSource that wraps the java.util.List obtained using the _THIS expression. Then, within the list's contents, define a TextField to display the individual values from the list.

Example Code:

JavaBean:

public class BeanWithList {

    private List<string> cities;
    private Integer id;

    // public getters for bean properties

}</string>

JRXML File:

<field name="id" class="java.lang.Integer"></field>
<field name="cities" class="java.util.Collection"></field>

<detail>
    <band height="20">
        <textfield>
            <reportelement x="0" y="0" width="100" height="20"></reportelement>
            <textfieldexpression></textfieldexpression>
        </textfield>
        <componentelement>
            <reportelement x="100" y="0" width="400" height="20"></reportelement>
            <list>
                <datasetrun subdataset="dataset1">
                    <datasourceexpression></datasourceexpression>
                </datasetrun>
                <listcontents height="20" width="400">
                    <textfield>
                        <reportelement x="0" y="0" width="100" height="20"></reportelement>
                        <textfieldexpression></textfieldexpression>
                    </textfield>
                </listcontents>
            </list>
        </componentelement>
    </band>
</detail>

Result:

The report will display the ID of the JavaBean along with the list of cities stored in its cities property.

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