报表变量是在报表表达式之上构建的特殊对象.
报表变量简化了以下任务 :
报表表达式，在整个报表模板中大量使用.这些表达式只能使用报表变量声明一次.
报表变量可以根据相应的表达式值执行各种计算，例如count，sum，average ，最低，最高，方差等.
如果在报表设计中定义了变量，那么这些变量可以被新变量引用表达式.因此，在报表设计中声明变量的顺序很重要.
变量声明如下 :
<variable name = "CityNumber" class = "java.lang.Integer" incrementType = "Group" incrementGroup = "CityGroup" calculation = "Count"> <variableExpression> <![CDATA[Boolean.TRUE]]> </variableExpression> </variable>
如上所示，< variable> element包含多个属性.这些属性总结如下 :
类似于参数和字段，</variable>的 name 属性元素是强制性的.它允许在报表表达式中通过其声明的名称引用变量.
类属性是也是强制性的，指定变量值的类名.它的默认值是 java.lang.String .这可以在报告编译时和报告填充时更改为类路径中可用的任何类.引擎在使用$ V {}标记的报表表达式中处理类型转换，因此不需要手动类型转换.
此属性确定&减去;填写报表时对变量执行的计算.以下小节描述< variable>的计算属性的所有可能值.元素.
平均值 : 变量值是变量表达式的每个非空值的平均值.仅对数字变量有效.
计数 : 变量值是变量表达式的非空实例的计数.
First : 变量值是变量表达式的第一个实例的值.后续值将被忽略.
最高&减去;变量值是变量表达式的最高值.
最低 : 变量值是报表中变量表达式的最小值.
Nothing : 不对变量进行任何计算.
StandardDeviation : 变量值是与报表表达式匹配的所有非空值的标准偏差.仅对数字变量有效.
Sum : 变量值是报表表达式返回的所有非空值的总和.
System : 变量值是一个自定义计算(使用JasperReports的scriptlet功能自己计算该变量的值).
Variance &减去;变量值是通过评估报表变量的表达式返回的所有非空值的方差.
此属性确定在填充报表上的当前记录时用于计算变量值的类.默认值是实现 net.sf.jasperreports.engine.fill.JRIncrementerFactory 的任何类.引擎将使用工厂类在运行时实例化增量对象，具体取决于为变量设置的计算属性.
这决定了何时重新计算变量的值.此属性使用值，如下面和下面;
列 : 变量值在每列末尾重新计算.
Group : 当incrementGroup指定的组发生更改时，将重新计算变量值.
无 : 每条记录都会重新计算变量值.
Page : 变量值在每页末尾重新计算.
报告 : 在报告结束时重新计算变量值一次.
这当 incrementType 是 Group 时，确定重新计算变量值的组的名称.这将获取JRXML报告模板中声明的任何组的名称.
这确定何时重置变量的值.此属性使用值，如下面和下面;
列 : 变量值在每列的开头重置.
Group : 当incrementGroup指定的组发生更改时，将重置变量值.
无 : 永远不会重置变量值.
Page : 变量值在每页开头重置.
报告 : 变量值仅在报告开头重置一次.
当 resetType 为 Group 时，这将确定重置变量值的组的名称.此属性的值将是JRXML报告模板中声明的任何组的名称.
有一些已构建-in系统变量，准备在表达式中使用，如下 :
| S.否 | 变量名称和描述 |
|---|---|
| 1 | PAGE_NUMBER 此变量的值是其当前页码.它可以用于使用JasperReports文本字段元素的特殊功能显示当前页码和总页数， evaluationTime 属性. |
| 2 | COLUMN_NUMBER 此变量包含当前列号. |
| 3 | REPORT_COUNT 此报表变量包含已处理的记录总数. |
| 4 | PAGE_COUNT 这变量包含生成当前页面时处理的记录数. |
| 5 | COLUMN_COUNT 此变量包含生成当前列时处理的记录数. |
| 6 | GroupName_COUNT 此变量的名称源自名称它对应的组，后缀为_COUNT序列.此变量包含当前组中的记录数. |
让我们在现有的报告模板中添加一个变量( countNumber )(章节报告设计 ).我们将计数前缀为每条记录.修订后的报告模板(jasper_report_template.jrxml)如下所示.将其保存到C:\tools\jasperreports-5.0.1 \ test目录 :
<?xml version = "1.0"?>
<!DOCTYPE jasperReport PUBLIC
"//JasperReports//DTD Report Design//EN"
"http://jasperreports.sourceforge.net/dtds/jasperreport.dtd">
<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" pageWidth = "595"
pageHeight = "842" columnWidth = "515"
leftMargin = "40" rightMargin = "40" topMargin = "50" bottomMargin = "50">
<parameter name = "ReportTitle" class = "java.lang.String"/>
<parameter name = "Author" class = "java.lang.String"/>
<queryString>
<![CDATA[]]>
</queryString>
<field name = "country" class = "java.lang.String">
<fieldDescription>
<![CDATA[country]]>
</fieldDescription>
</field>
<field name = "name" class = "java.lang.String">
<fieldDescription>
<![CDATA[name]]>
</fieldDescription>
</field>
<variable name = "countNumber" class = "java.lang.Integer" calculation = "Count">
<variableExpression>
<![CDATA[Boolean.TRUE]]>
</variableExpression>
</variable>
<title>
<band height = "70">
<line>
<reportElement x = "0" y = "0" width = "515" height = "1"/>
</line>
<textField isBlankWhenNull = "true" bookmarkLevel = "1">
<reportElement x = "0" y = "10" width = "515" height = "30"/>
<textElement textAlignment = "Center">
<font size = "22"/>
</textElement>
<textFieldExpression class = "java.lang.String">
<![CDATA[$P{ReportTitle}]]>
</textFieldExpression>
<anchorNameExpression>
<![CDATA["Title"]]>
</anchorNameExpression>
</textField>
<textField isBlankWhenNull = "true">
<reportElement x = "0" y = "40" width = "515" height = "20"/>
<textElement textAlignment = "Center">
<font size = "10"/>
</textElement>
<textFieldExpression class = "java.lang.String">
<![CDATA[$P{Author}]]>
</textFieldExpression>
</textField>
</band>
</title>
<columnHeader>
<band height = "23">
<staticText>
<reportElement mode = "Opaque" x = "0" y = "3" width = "535" height = "15"
backcolor = "#70A9A9" />
<box>
<bottomPen lineWidth = "1.0" lineColor = "#CCCCCC" />
</box>
<textElement />
<text>
<![CDATA[]]>
</text>
</staticText>
<staticText>
<reportElement x = "414" y = "3" width = "121" height = "15" />
<textElement textAlignment = "Center" verticalAlignment = "Middle">
<font isBold = "true" />
</textElement>
<text><![CDATA[Country]]></text>
</staticText>
<staticText>
<reportElement x = "0" y = "3" width = "136" height = "15" />
<textElement textAlignment = "Center" verticalAlignment = "Middle">
<font isBold = "true" />
</textElement>
<text><![CDATA[Name]]></text>
</staticText>
</band>
</columnHeader>
<detail>
<band height = "16">
<staticText>
<reportElement mode = "Opaque" x = "0" y = "0" width = "535" height = "14"
backcolor = "#E5ECF9" />
<box>
<bottomPen lineWidth = "0.25" lineColor = "#CCCCCC" />
</box>
<textElement />
<text>
<![CDATA[]]>
</text>
</staticText>
<textField>
<reportElement x = "414" y = "0" width = "121" height = "15" />
<textElement textAlignment = "Center" verticalAlignment = "Middle">
<font size = "9" />
</textElement>
<textFieldExpression class = "java.lang.String">
<![CDATA[$F{country}]]>
</textFieldExpression>
</textField>
<textField>
<reportElement x = "0" y = "0" width = "136" height = "15" />
<textElement textAlignment = "Center" verticalAlignment = "Middle" />
<textFieldExpression class = "java.lang.String">
<![CDATA[" " + String.valueOf($V{countNumber}) +"."+$F{name}]]>
</textFieldExpression>
</textField>
</band>
</detail>
</jasperReport>报告填充的java代码保持不变.文件 C:\tools\jasperreports-5.0.1\test\src\com\it1352\ JapersReportFill.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.JasperFillManager;
import net.sf.jasperreports.engine.data.JRBeanCollectionDataSource;
public class JasperReportFill {
@SuppressWarnings("unchecked")
public static void main(String[] args) {
String sourceFileName =
"C://tools/jasperreports-5.0.1/test/jasper_report_template.jasper";
DataBeanList DataBeanList = new DataBeanList();
ArrayList<DataBean> dataList = DataBeanList.getDataBeanList();
JRBeanCollectionDataSource beanColDataSource =
new JRBeanCollectionDataSource(dataList);
Map parameters = new HashMap();
/**
* Passing ReportTitle and Author as parameters
*/
parameters.put("ReportTitle", "List of Contacts");
parameters.put("Author", "Prepared By Manisha");
try {
JasperFillManager.fillReportToFile(
sourceFileName, parameters, beanColDataSource);
} catch (JRException e) {
e.printStackTrace();
}
}
}POJO文件的内容 C:\tools\jasperreports -5.0.1\test\src\com\it1352\ DataBean.java 如下所示 :
package com.it1352;
public class DataBean {
private String name;
private String country;
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;
}
}文件的内容 C:\tools\jasperreports-5.0.1 \ test \src\com\it1352\ DataBeanList.java 如下所示 :
package com. it1352;
import java.util.ArrayList;
public class DataBeanList {
public ArrayList<DataBean> getDataBeanList() {
ArrayList<DataBean> dataBeanList = new ArrayList<DataBean>();
dataBeanList.add(produce("Manisha", "India"));
dataBeanList.add(produce("Dennis Ritchie", "USA"));
dataBeanList.add(produce("V.Anand", "India"));
dataBeanList.add(produce("Shrinath", "California"));
return dataBeanList;
}
/**
* This method returns a DataBean object,
* with name and country set in it.
*/
private DataBean produce(String name, String country) {
DataBean dataBean = new DataBean();
dataBean.setName(name);
dataBean.setCountry(country);
return dataBean;
}
}我们将编译并执行上述文件我们定期的ANT构建过程.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挑选出来的，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.JasperReportFill (viewFullReport是默认目标)为 :
C:\tools\jasperreports-5.0.1\test>ant -Dmain-class=com.IT屋.JasperReportFill Buildfile: C:\tools\jasperreports-5.0.1\test\build.xml clean-sample: [delete] Deleting directory C:\tools\jasperreports-5.0.1\test\classes [delete] Deleting: C:\tools\jasperreports-5.0.1\test\jasper_report_template.jasper [delete] Deleting: C:\tools\jasperreports-5.0.1\test\jasper_report_template.jrprint 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 build.sysclasspath=last; set to false for repeatable builds [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.JasperReportFill [java] log4j:WARN No appenders could be found for logger (net.sf.jasperreports.extensions.ExtensionsEnvironment). [java] log4j:WARN Please initialize the log4j system properly. 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: 18 seconds
由于上面的编译，JasperViewer窗口打开为在屏幕下方 :
在这里，我们看到每个记录的前缀都是计数.
