如何在Jasper Reports中从JSON数据源渲染嵌套表格？

问题背景 #

JSON数据源 #

{
   "details": [
       {
           "name": "Name 1",
           "head": [
               {
                   "isin": "ISIN 1",
                   "coupon": "Coupon 1"
               }
           ]
       },
       {
           "name": "Name 2",
           "head": [
               {
                   "isin": "ISIN 2",
                   "coupon": "Coupon 2"
               }
           ]
       }
   ]
}

期望渲染效果 #

依次展示以下独立表格：

1. 仅包含Name 1表头的表格
2. 包含ISIN 1、Coupon 1表头的表格
3. 仅包含Name 2表头的表格
4. 包含ISIN 2、Coupon 2表头的表格

现有Jasper报表代码 #

<?xml version="1.0" encoding="UTF-8"?>
<jasperReport uuid="13bb06fa-a8ce-41f8-b3e4-a094f892f221">
    <property name="com.jaspersoft.studio.data.defaultdataadapter" value="JSONAdapter"/>
    <subDataset name="datasetDetails" uuid="3f8c902f-fffd-48fe-b65f-46e976854490">
        <property name="com.jaspersoft.studio.data.defaultdataadapter" value="JSONAdapter"/>
        <queryString language="json">
            <![CDATA[details]]>
        </queryString>
        <field name="name" class="java.lang.String">
            <property name="net.sf.jasperreports.json.field.expression" value="name"/>
            <fieldDescription><![CDATA[name]]></fieldDescription>
        </field>
        <field name="head" class="net.sf.jasperreports.engine.data.JsonDataSource">
            <property name="net.sf.jasperreports.json.field.expression" value="head"/>
            <fieldDescription><![CDATA[head]]></fieldDescription>
        </field>
    </subDataset>
    <subDataset name="datasetDetailsHead" uuid="a91998cc-c1fa-4802-868d-90cb9a24636d">
        <property name="com.jaspersoft.studio.data.defaultdataadapter" value="JSONAdapter"/>
        <queryString language="json">
            <![CDATA[details.head]]>
        </queryString>
        <field name="isin" class="java.lang.String">
            <property name="net.sf.jasperreports.json.field.expression" value="isin"/>
            <fieldDescription><![CDATA[isin]]></fieldDescription>
        </field>
        <field name="coupon" class="java.lang.String">
            <property name="net.sf.jasperreports.json.field.expression" value="coupon"/>
            <fieldDescription><![CDATA[coupon]]></fieldDescription>
        </field>
    </subDataset>
    <queryString language="JSON">
        <![CDATA[]]>
    </queryString>
    <detail>
        <band>
            <componentElement>
                <jr:table xmlns:jr="http://jasperreports.sourceforge.net/jasperreports/components" xsi:schemaLocation="http://jasperreports.sourceforge.net/jasperreports/components http://jasperreports.sourceforge.net/xsd/components.xsd">
                    <datasetRun subDataset="datasetDetails" uuid="3ca38bbd-cd5a-44c4-98bb-2e993e3a4fc4">
                        <dataSourceExpression><![CDATA[((net.sf.jasperreports.engine.data.JsonDataSource)$P{REPORT_DATA_SOURCE}).subDataSource("details")]]></dataSourceExpression>
                    </datasetRun>
                    <jr:column>
                        <jr:detailCell>
                            <frame>
                                <textField>
                                    <textFieldExpression><![CDATA[$F{name}]]></textFieldExpression>
                                </textField>
                            </frame>
                            <frame>
                                <componentElement>
                                    <jr:table>
                                        <datasetRun subDataset="datasetDetailsHeadBond" uuid="998a8505-69bb-493a-8c3a-5dc7a0e62d42">
                                            <dataSourceExpression><![CDATA[((net.sf.jasperreports.engine.data.JsonDataSource)$P{REPORT_DATA_SOURCE}).subDataSource("details.head")]]></dataSourceExpression>
                                        </datasetRun>
                                        <jr:column>
                                            <jr:detailCell>
                                                <textField>
                                                    <textFieldExpression><![CDATA[$F{isin}]]></textFieldExpression>
                                                </textField>
                                            </jr:detailCell>
                                        </jr:column>
                                        <jr:column >
                                            <jr:detailCell >
                                                <textField>
                                                    <textFieldExpression><![CDATA[$F{coupon}]]></textFieldExpression>
                                                </textField>
                                            </jr:detailCell>
                                        </jr:column>
                                    </jr:table>
                                </componentElement>
                            </frame>
                        </jr:detailCell>
                    </jr:column>
                </jr:table>
            </componentElement>
        </band>
    </detail>
</jasperReport>

问题现象 #

渲染报表时，仅能看到外层的Name 1、Name 2数据，嵌套的head（ISIN、Coupon）数据完全无法展示。

修复步骤与修正代码 #

核心问题分析 #

1. 子数据集名称不匹配：嵌套表格引用的子数据集是datasetDetailsHeadBond，但实际定义的是datasetDetailsHead，名称错误导致无法找到对应数据集。
2. 数据源上下文错误：内层表格直接使用REPORT_DATA_SOURCE获取details.head，会遍历所有head数据，而非当前外层行对应的专属head数据。应该使用外层数据集里定义的$F{head}字段（已映射为JsonDataSource类型）作为内层表格的数据源。
3. 内层数据集queryString冗余：内层数据集不需要指定details.head作为查询路径，因为已经基于当前行的head数据源，直接留空即可。

修正后的完整代码 #

<?xml version="1.0" encoding="UTF-8"?>
<jasperReport uuid="13bb06fa-a8ce-41f8-b3e4-a094f892f221">
    <property name="com.jaspersoft.studio.data.defaultdataadapter" value="JSONAdapter"/>
    <subDataset name="datasetDetails" uuid="3f8c902f-fffd-48fe-b65f-46e976854490">
        <property name="com.jaspersoft.studio.data.defaultdataadapter" value="JSONAdapter"/>
        <queryString language="json">
            <![CDATA[details]]>
        </queryString>
        <field name="name" class="java.lang.String">
            <property name="net.sf.jasperreports.json.field.expression" value="name"/>
            <fieldDescription><![CDATA[name]]></fieldDescription>
        </field>
        <field name="head" class="net.sf.jasperreports.engine.data.JsonDataSource">
            <property name="net.sf.jasperreports.json.field.expression" value="head"/>
            <fieldDescription><![CDATA[head]]></fieldDescription>
        </field>
    </subDataset>
    <subDataset name="datasetDetailsHead" uuid="a91998cc-c1fa-4802-868d-90cb9a24636d">
        <property name="com.jaspersoft.studio.data.defaultdataadapter" value="JSONAdapter"/>
        <queryString language="json">
            <![CDATA[]]>
        </queryString>
        <field name="isin" class="java.lang.String">
            <property name="net.sf.jasperreports.json.field.expression" value="isin"/>
            <fieldDescription><![CDATA[isin]]></fieldDescription>
        </field>
        <field name="coupon" class="java.lang.String">
            <property name="net.sf.jasperreports.json.field.expression" value="coupon"/>
            <fieldDescription><![CDATA[coupon]]></fieldDescription>
        </field>
    </subDataset>
    <queryString language="JSON">
        <![CDATA[]]>
    </queryString>
    <detail>
        <band>
            <componentElement>
                <jr:table xmlns:jr="http://jasperreports.sourceforge.net/jasperreports/components" xsi:schemaLocation="http://jasperreports.sourceforge.net/jasperreports/components http://jasperreports.sourceforge.net/xsd/components.xsd">
                    <datasetRun subDataset="datasetDetails" uuid="3ca38bbd-cd5a-44c4-98bb-2e993e3a4fc4">
                        <dataSourceExpression><![CDATA[((net.sf.jasperreports.engine.data.JsonDataSource)$P{REPORT_DATA_SOURCE}).subDataSource("details")]]></dataSourceExpression>
                    </datasetRun>
                    <jr:column>
                        <jr:detailCell>
                            <!-- 显示Name的表格 -->
                            <frame>
                                <textField>
                                    <textFieldExpression><![CDATA[$F{name}]]></textFieldExpression>
                                </textField>
                            </frame>
                            <!-- 嵌套显示head数据的表格 -->
                            <frame>
                                <componentElement>
                                    <jr:table>
                                        <datasetRun subDataset="datasetDetailsHead" uuid="998a8505-69bb-493a-8c3a-5dc7a0e62d42">
                                            <!-- 使用当前行的head字段作为数据源 -->
                                            <dataSourceExpression><![CDATA[$F{head}]]></dataSourceExpression>
                                        </datasetRun>
                                        <jr:column>
                                            <jr:detailCell>
                                                <textField>
                                                    <textFieldExpression><![CDATA[$F{isin}]]></textFieldExpression>
                                                </textField>
                                            </jr:detailCell>
                                        </jr:column>
                                        <jr:column>
                                            <jr:detailCell>
                                                <textField>
                                                    <textFieldExpression><![CDATA[$F{coupon}]]></textFieldExpression>
                                                </textField>
                                            </jr:detailCell>
                                        </jr:column>
                                    </jr:table>
                                </componentElement>
                            </frame>
                        </jr:detailCell>
                    </jr:column>
                </jr:table>
            </componentElement>
        </band>
    </detail>
</jasperReport>

内容的提问来源于stack exchange，提问作者Evgeniy