报表表达式是JasperReports的强大功能，它允许我们在报表上显示计算数据.计算数据是不是静态数据的数据，不作为报告参数或数据源字段专门传递.报表表达式是通过组合报表参数，字段和静态数据构建的.默认情况下，Java语言用于编写报表表达式. JasperReports编译器支持报表表达式的其他脚本语言，如Groovy脚本语言，JavaScript或BeanShell脚本.
本章将解释你和减去;报表表达式如何工作，假设它们仅使用Java语言编写.在JRXML报告模板中，有几个元素将表达式定义为 :
< variableExpression>
< initialValueExpression>
< groupExpression>
< printWhenExpression>
< ; imageExpression>
< textFieldExpression>
基本上，所有报表表达式都是Java表达式，可以引用报表字段，报表变量和报表参数.
要在表达式中使用报表字段引用时，字段名称必须放在 $ F {和} 字符序列之间，如下所示 :
<textfieldexpression>
$F{Name}
</textfieldexpression>以下是我们现有JRXML文件中的一段代码(报告)设计 :
<textFieldExpression class = "java.lang.String">
<![CDATA[$F{country}]]>
</textFieldExpression>要引用表达式中的变量，我们必须将变量的名称放在 $ V {和} ，如下面给出的示例所示 :
<textfieldexpression>
"Total height : " + $V{SumOfHeight} + " ft."
</textfieldexpression>要引用表达式中的参数，参数的名称应放在 $ P {和} ，如下面给出的示例所示 :
<textfieldexpression>
"ReportTitle : " + $P{Title}
</textfieldexpression>以下是我们现有JRXML文件中的一段代码，它演示了表达式中参数的引用. (章节报告设计中的JRXML) :
<textField isBlankWhenNull = "true" bookmarkLevel = "1">
<reportElement x = "0" y = "10" width = "515" height = "30"/>
<textElement textAlignment = "Center">
<font size = "22"/>
</textElement>
<textFieldExpression class = "java.lang.String">
<![CDATA[$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>如上所述，参数，字段和变量引用实际上是真正的Java对象.从报表模板中的参数，字段或变量声明中了解它们的类，我们甚至可以在表达式中调用这些对象引用的方法.
以下示例显示 : 如何从java.lang.String报告字段中提取和显示第一个字母"Name" :
<textFieldExpression>
$F{Name}.substring(0, 1)
</textFieldExpression>要引用表达式中的资源，键应该放在 $ R {和} 之间，如下面给出的示例所示 :
<textfieldexpression>
$R{report.title}
</textfieldexpression>根据运行时提供的区域设置和 report.title 键，加载与报告模板关联的资源包.因此，通过从资源包中提取String值来显示报告的标题.有关国际化的更多信息，请参阅国际化一章.
计算器是JasperReports中的一个实体，它在报告填充时评估表达式并递增变量或数据集.在编译过程中，编译器会生成信息并将其存储在编译报告中.在报告填充期间使用此信息来构建net.sf.jasperreports.engine.fill.JRCalculator类的实例.
Java源文件由Java生成和编译基于报告的编译器.这个生成的类是JRCalculator的子类，通过编译生成的字节码存储在JasperReport对象中.这个bytcode在报告填充时加载，生成的类被实例化以获得表达式评估所需的计算器对象.
JasperReports在定义变量表达式时不支持if-else语句.相反，您可以使用三元运算符 {cond}？ {声明1}:{声明2} .此运算符可以嵌套在Java表达式中，以根据多个条件获得所需的输出.
让我们修改现有的报告模板(章报告设计)并为字段国家/地区添加条件表达式.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>
<sortField name = "country" order = "Descending"/>
<sortField name = "name"/>
<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}.isEmpty() ? "NO COUNTRY" : $F{country}]]>
</textFieldExpression>
</textField>
<textField>
<reportElement x = "0" y = "0" width = "136" height = "15" />
<textElement textAlignment = "Center" verticalAlignment = "Middle" />
<textFieldExpression class = "java.lang.String">
<![CDATA[$F{name}]]>
</textFieldExpression>
</textField>
</band>
</detail>
</jasperReport>报告填写的java代码如下.文件 C:\tools\jasperreports-5.0.1\test\src\com\it1352\ JapersReportFill.java 的内容为 :
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 是 :
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;
}
}我们将在Java bean列表中添加一个国家/地区字段为空的新记录.文件 C:\tools\jasperreports-5.0.1\test\src\com\it1352\DataBeanList.java 的内容为 :
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"));
dataBeanList.add(produce("Tanmay", ""));
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从环境设置一章中挑选，并且应该与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 3 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: 5 minutes 5 seconds C:\tools\jasperreports-5.0.1\test>
作为上述编译的结果，JasperViewer窗口打开，如下面给出的屏幕所示 :
在这里，我们可以看到，对于最后一条记录，我们没有传递该字段国家的任何数据，"否正在印刷"国家".
