子报告是JasperReports的一个很好的功能.此功能允许在另一个报表中合并报表，也就是说，一个报表可以是另一个报表的子报表.子报告可以帮助我们简化报表设计，因为我们可以创建许多简单的报表并将它们封装到主报表中.子报表的编译和填充就像普通报告一样.任何报告模板在合并到另一个报告模板时都可以用作子报告，而(报告模板的内部)没有任何更改.
子报告就像普通的报告模板一样.它们实际上是 net.sf.jasperreports.engine.JasperReport 对象，它们是在编译 net.sf.jasperreports.engine.design.JasperDesign对象后获得的.
A< subreport>将子报表引入主报表时使用元素.以下是< subreport>中的子元素列表. JRXML元素.
< reportElement>
<parametersMapExpression>:这用于将包含报表参数的映射传递到子报表.映射通常从主报表中的参数获取，或者使用内置的REPORTS_PARAMETERS_MAP参数将父报表的参数传递给子报表.该表达式应始终返回 java.util.Map 对象，其中键是参数
names.
<subreportParameter> :此元素用于将参数传递到子报表.它有一个属性 name ，这是强制性的.
< connectionExpression> :这用于将 java.sql.Connection 传递给子报表.仅在子报表模板在报表填充阶段需要数据库连接时才使用它.
< dataSourceExpression>:这用于将数据源传递到子报表.此数据源通常从主报表中的参数获取，或者使用内置的REPORT_DATA_SOURCE参数将父报表的数据源传递到子报表.
元素( connectionExpression和dataSourceExpression )不能同时出现在< subreport>中.元素声明.这是因为我们无法同时提供数据源和子报表的连接.我们必须决定其中一个并坚持下去.
< returnValue> :这用于将其中一个子报表变量的值分配给主报表的变量之一.此子元素的属性如下 :
subreportVariable : 此属性指定要返回其值的子报表变量的名称.
toVariable : 此属性指定父报表变量的名称，其值将使用子报表中的值进行复制/递增.
计算 : 此属性可以取值:Nothing，Count，DistinctCount，Sum，Average，Lowest，Highest，StandardDeviation，Variance.属性计算的默认值为"Nothing".
incrementerFactoryClass : 此属性指定用于创建增量器实例的工厂类.
< subreportExpression>:这表示在何处查找子报表的已编译报表模板.此元素具有类属性. 类属性可以采用以下任何值:java.lang.String，java.io.File，java.net.URL，java.io.InputStream，net.sf.jasperreports.engine.JasperReport .默认值为 java.lang.String .
isUsingCache : 这是< subreport>的属性.元件.这是一个布尔值，当设置为 true 时，报告引擎将尝试使用其指定的源识别先前加载的子报告模板对象.此缓存功能仅适用于具有表达式的子报表元素，这些表达式将java.lang.String对象作为子报表模板源返回，表示文件名，URL或类路径资源.
让我们举一个简单的例子来演示使用JRDataSource创建子报表.让我们先写两个新的报告模板，一个是子报告，另一个是主报告.子报表(address_report_template.jrxml)模板的内容如下所示.将其保存到C:\tools\jasperreports-5.0.1 \ test目录.
<?xml version = "1.0" encoding = "UTF-8"?>
<jasperReport
xmlns = "http://jasperreports.sourceforge.net/jasperreports"
xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation = "http://jasperreports.sourceforge.net/jasperreports
http://jasperreports.sourceforge.net/xsd/jasperreport.xsd"
name = "address_report_template" pageWidth = "175" pageHeight = "842"
columnWidth = "175" leftMargin = "0" rightMargin = "0"
topMargin = "0" bottomMargin = "0">
<field name = "city" class = "java.lang.String"/>
<field name = "street" class = "java.lang.String"/>
<background>
<band splitType = "Stretch"/>
</background>
<title>
<band height = "20" splitType = "Stretch">
<staticText>
<reportElement x = "0" y = "0" width = "100" height = "20"/>
<textElement>
<font size = "14" isBold = "true"/>
</textElement>
<text><![CDATA[Addresses]]></text>
</staticText>
</band>
</title>
<pageHeader>
<band height = "12" splitType = "Stretch"/>
</pageHeader>
<columnHeader>
<band height = "12" splitType = "Stretch"/>
</columnHeader>
<detail>
<band height = "27" splitType = "Stretch">
<textField>
<reportElement x = "0" y = "0" width = "120" height = "20"/>
<textElement>
<font size = "12" isBold = "true"/>
</textElement>
<textFieldExpression class = "java.lang.String">
<![CDATA[$F{city}+" Address:"]]>
</textFieldExpression>
</textField>
<textField isStretchWithOverflow = "true">
<reportElement x = "120" y = "0" width = "435" height = "20"/>
<textElement>
<font size = "12"/>
</textElement>
<textFieldExpression class = "java.lang.String">
<![CDATA[$F{street}]]>
</textFieldExpression>
</textField>
</band>
</detail>
<columnFooter>
<band height = "8" splitType = "Stretch"/>
</columnFooter>
<pageFooter>
<band height = "11" splitType = "Stretch"/>
</pageFooter>
<summary>
<band height = "9" splitType = "Stretch"/>
</summary>
</jasperReport>当我们使用数据源时，我们需要编写相应的POJO文件 SubReportBean.java ，如下所示.将其保存到目录C:\tools \jasperreports-5.0.1 \ test \ src \ com \ it1352 :
package com.it1352;
public class SubReportBean {
private String city;
private String street;
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getStreet() {
return street;
}
public void setStreet(String street) {
this.street = street;
}
}在这里，我们宣布了两个字段'city'和'街道'和相应的getter和setter方法已定义.
现在，让我们更新现有的 DataBean 文件.我们将添加一个新字段 subReportBeanList ，它是一个java.util.List.该字段将保存SubReportBean对象的列表. DataBean文件的内容如下.将其保存到目录C:\tools \jasperreports-5.0.1\test \ src \ com \ it1352.
package com.it1352;
import java.util.List;
public class DataBean {
private String name;
private String country;
private List<SubReportBean> subReportBeanList;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
public List<SubReportBean> getSubReportBeanList() {
return subReportBeanList;
}
public void setSubReportBeanList(List<SubReportBean> subReportBeanList) {
this.subReportBeanList = subReportBeanList;
}
}我们现在更新文件C:\tools \ jasperreports-5.0.1 \ test \ src\com\it1352\的 DataBeanList.java 的.该文件的内容为 :
package com.it1352;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class DataBeanList {
public ArrayList<DataBean> getDataBeanList() {
// Create sub report data
SubReportBean subBean1 = new SubReportBean();
subBean1.setCity("Mumbai");
subBean1.setStreet("M.G.Road");
SubReportBean subBean2 = new SubReportBean();
subBean2.setCity("New York");
subBean2.setStreet("Park Street");
SubReportBean subBean3 = new SubReportBean();
subBean3.setCity("San Fransisco");
subBean3.setStreet("King Street");
ArrayList<DataBean> dataBeanList = new ArrayList<DataBean>();
// Create master report data
dataBeanList.add(produce("Manisha", "India",
Arrays.asList(subBean1)));
dataBeanList.add(produce("Dennis Ritchie", "USA",
Arrays.asList(subBean2)));
dataBeanList.add(produce("V.Anand", "India",
Arrays.asList(subBean1)));
dataBeanList.add(produce("Shrinath", "California",
Arrays.asList(subBean3)));
return dataBeanList;
}
/*
* This method returns a DataBean object,
* with name, country and sub report
* bean data set in it.
*/
private DataBean produce(String name, String country,
List<SubReportBean> subBean) {
DataBean dataBean = new DataBean();
dataBean.setName(name);
dataBean.setCountry(country);
dataBean.setSubReportBeanList(subBean);
return dataBean;
}
}在上面文件的方法produ()中，我们设置了SubReportBean的列表.
现在，让我们编写一个新的主报告模板(jasper_report_template.jrxml).将此文件保存到目录 C:\tools\jasperreports-5.0.1 \ test .该文件的内容如下 :
<?xml version = "1.0" encoding = "UTF-8"?>
<jasperReport xmlns = "http://jasperreports.sourceforge.net/jasperreports"
xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation = "http://jasperreports.sourceforge.net/jasperreports
http://jasperreports.sourceforge.net/xsd/jasperreport.xsd"
name = "jasper_report_template" language = "groovy" pageWidth = "595"
pageHeight = "842" columnWidth ="555" leftMargin = "20" rightMargin = "20"
topMargin = "20" bottomMargin = "20">
<parameter name = "SUBREPORT_DIR" class = "java.lang.String" isForPrompting = "false">
<defaultValueExpression>
<![CDATA["C:\\tools\\jasperreports-5.0.1\\test\]]>
</defaultValueExpression>
</parameter>
<field name = "country" class = "java.lang.String"/>
<field name = "name" class = "java.lang.String"/>
<field name = "subReportBeanList" class = "java.util.List"/>
<background>
<band splitType = "Stretch"/>
</background>
<title>
<band height = "35" splitType = "Stretch">
<staticText>
<reportElement x = "0" y = "0" width = "204" height = "34"/>
<textElement>
<font size = "26" isBold = "true"/>
</textElement>
<text><![CDATA[Contact Report]]></text>
</staticText>
</band>
</title>
<pageHeader>
<band height = "17" splitType = "Stretch"/>
</pageHeader>
<columnHeader>
<band height = "21" splitType = "Stretch"/>
</columnHeader>
<detail>
<band height = "112" splitType = "Stretch">
<staticText>
<reportElement x = "0" y = "0" width = "100" height = "20"/>
<textElement>
<font size = "12" isBold = "true"/>
</textElement>
<text><![CDATA[Name:]]></text>
</staticText>
<staticText>
<reportElement x = "0" y = "20" width = "100" height = "20"/>
<textElement>
<font size = "12" isBold = "true"/>
</textElement>
<text><![CDATA[Country:]]></text>
</staticText>
<textField>
<reportElement x = "104" y = "0" width = "277" height = "20"/>
<textElement>
<font size = "12"/>
</textElement>
<textFieldExpression class = "java.lang.String">
<![CDATA[$F{name}]]>
</textFieldExpression>
</textField>
<textField>
<reportElement x = "104" y = "20" width = "277" height = "20"/>
<textElement>
<font size = "12"/>
</textElement>
<textFieldExpression class = "java.lang.String">
<![CDATA[$F{country}]]>
</textFieldExpression>
</textField>
<subreport>
<reportElement positionType = "Float" x = "335" y = "25" width = "175"
height = "20" isRemoveLineWhenBlank = "true" backcolor = "#99ccff"/>
<dataSourceExpression>
new net.sf.jasperreports.engine.data.JRBeanCollectionDataSource
($F{subReportBeanList})
</dataSourceExpression>
<subreportExpression class = "java.lang.String">
<![CDATA[$P{SUBREPORT_DIR} + "address_report_template.jasper"]]>
</subreportExpression>
</subreport>
<line>
<reportElement x = "0" y = "50" width = "550" height = "1"/>
</line>
</band>
</detail>
<columnFooter>
<band height = "19" splitType = "Stretch"/>
</columnFooter>
<pageFooter>
<band height = "18" splitType = "Stretch"/>
</pageFooter>
<summary>
<band height = "14" splitType = "Stretch"/>
</summary>
</jasperReport>在上面的模板中，我们定义了一个新参数"SUBREPORT_DIR"，它定义了子报表的路径.我们定义了一个 java.util.List，类型的字段 subReportBeanList ，它对应于DataBean文件中的属性.元素<子报告>有子元素< dataSourceExpression>.我们已将列表 subReportBeanList 放在JRBeanCollectionDataSource的实例中.在子元素< subreportExpression/>中，我们给出了子报告名称(AddressReport.jasper).
现在，让我们编写一个新类 CreateReport 编译和执行我们的报告模板.文件 C:\tools\jasperreports-5.0.1 \test\src\com\it1352\CreateReport.java 的内容如下所示 :
package com.it1352;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import net.sf.jasperreports.engine.JRException;
import net.sf.jasperreports.engine.JasperCompileManager;
import net.sf.jasperreports.engine.JasperFillManager;
import net.sf.jasperreports.engine.JasperReport;
import net.sf.jasperreports.engine.data.JRBeanCollectionDataSource;
public class CreateReport {
public static void main(String[] args) {
String masterReportFileName = "C://tools/jasperreports-5.0.1/test"
+ "/jasper_report_template.jrxml";
String subReportFileName = "C://tools/jasperreports-5.0.1/test"
+ "/AddressReport.jrxml";
String destFileName = "C://tools/jasperreports-5.0.1/test"
+ "/jasper_report_template.JRprint";
DataBeanList DataBeanList = new DataBeanList();
ArrayList<DataBean> dataList = DataBeanList.getDataBeanList();
JRBeanCollectionDataSource beanColDataSource = new
JRBeanCollectionDataSource(dataList);
try {
/* Compile the master and sub report */
JasperReport jasperMasterReport = JasperCompileManager
.compileReport(masterReportFileName);
JasperReport jasperSubReport = JasperCompileManager
.compileReport(subReportFileName);
Map<String, Object> parameters = new HashMap<String, Object>();
parameters.put("subreportParameter", jasperSubReport);
JasperFillManager.fillReportToFile(jasperMasterReport,
destFileName, parameters, beanColDataSource);
} catch (JRException e) {
e.printStackTrace();
}
System.out.println("Done filling!!! ...");
}
}在这里，我们看到我们正在编译主报告模板和子报告模板并传递主报告(.报告填写的jasper文件.
现在，我们所有文件都准备好了，让我们使用常规的ANT构建来编译和执行它们处理.文件build.xml的内容(保存在目录C:\tools\jasperreports-5.0.1 \ test下面)如下所示.
导入文件 - baseBuild. xml是从环境设置一章中选取的，应该与build.xml放在同一目录中.
<?xml version = "1.0" encoding = "UTF-8"?>
<project name = "JasperReportTest" default = "viewFillReport" basedir = ".">
<import file = "baseBuild.xml" />
<target name = "viewFillReport" depends = "compile,compilereportdesing,run"
description = "Launches the report viewer to preview the
report stored in the .JRprint file.">
<java classname = "net.sf.jasperreports.view.JasperViewer" fork = "true">
<arg value = "-F${file.name}.JRprint" />
<classpath refid = "classpath" />
</java>
</target>
<target name = "compilereportdesing" description = "Compiles the JXML file and
produces the .jasper file.">
<taskdef name = "jrc" classname = "net.sf.jasperreports.ant.JRAntCompileTask">
<classpath refid = "classpath" />
</taskdef>
<jrc destdir = ".">
<src>
<fileset dir = ".">
<include name = "*.jrxml" />
</fileset>
</src>
<classpath refid = "classpath" />
</jrc>
</target>
</project>接下来，让我们打开命令行窗口并转到build.xml所在的目录.最后，执行命令 ant -Dmain-class = com.it1352.CreateReport (viewFullReport是默认目标)，如下 :
Buildfile: C:\tools\jasperreports-5.0.1\test\build.xml clean-sample: [delete] Deleting directory C:\tools\jasperreports-5.0.1\test\classes compile: [mkdir] Created dir: C:\tools\jasperreports-5.0.1\test\classes [javac] C:\tools\jasperreports-5.0.1\test\baseBuild.xml:28: warning: 'includeantruntime' was not set, defaulting to [javac] Compiling 7 source files to C:\tools\jasperreports-5.0.1\test\classes compilereportdesing: [jrc] Compiling 1 report design files. [jrc] log4j:WARN No appenders could be found for logger (net.sf.jasperreports.engine.xml.JRXmlDigesterFactory). [jrc] log4j:WARN Please initialize the log4j system properly. [jrc] log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info. [jrc] File : C:\tools\jasperreports-5.0.1\test\ jasper_report_template.jrxml ... OK. run: [echo] Runnin class : com.IT屋.CreateReport [java] Compiling Report Design ... [java] log4j:WARN No appenders could be found for logger (net.sf.jasperreports.engine.xml.JRXmlDigesterFactory). [java] log4j:WARN Please initialize the log4j system properly. [java] Done filling!!! ... viewFillReport: [java] log4j:WARN No appenders could be found for logger (net.sf.jasperreports.extensions.ExtensionsEnvironment). [java] log4j:WARN Please initialize the log4j system properly. BUILD SUCCESSFUL Total time: 72 minutes 13 seconds
由于上面的编译，JasperViewer窗口打开up如下面给出的屏幕所示 :
在这里，我们可以看到显示属性Name，Country和Address.
