报表表达式

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出的数据。计算出的数据不是静态数据，也不是作为报表参数或数据源字段专门传递的数据。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 编译器支持其他用于报表表达式的脚本语言，如 Groovy 脚本语言、JavaScript 或 BeanShell 脚本。

本章将向您解释 - 报表表达式是如何工作的，假设它们仅使用 Java 语言编写。在 JRXML 报表模板中，有几个元素定义了表达式，如下所示：

<variableExpression>
<initialValueExpression>
<groupExpression>
<printWhenExpression>
<imageExpression>
<textFieldExpression>

表达式声明

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。

表达式中的字段引用

要在表达式中使用报表字段引用，必须将字段名称放在$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（章节报表设计）中的一段代码：

<textFieldExpression class = "java.lang.String">
   <![CDATA[$F{country}]]>
</textFieldExpression>

表达式中的变量引用

要在表达式中引用变量，必须将变量名称放在$V{和}之间，如下例所示：

<textfieldexpression>
   "Total height : " + $V{SumOfHeight} + " ft."
</textfieldexpression>

表达式中的参数引用

要在表达式中引用参数，应将参数名称放在$P{和}之间，如下例所示：

<textfieldexpression>
   "ReportTitle : " + $P{Title}
</textfieldexpression>

以下是我们现有 JRXML 文件中的一段代码，它演示了在表达式中引用参数。（来自章节报表设计的 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实的 Java 对象。了解报表模板中参数、字段或变量声明的类，我们甚至可以在表达式中调用这些对象引用的方法。

以下示例显示了 - 如何从 java.lang.String 报表字段“Name”中提取并显示第一个字母：

<textFieldExpression>
   $F{Name}.substring(0, 1)
</textFieldExpression>

表达式中的资源包引用

要在表达式中引用资源，应将键放在$R{和}之间，如下例所示：

<textfieldexpression>
   $R{report.title}
</textfieldexpression>

根据运行时提供的区域设置和report.title键，加载与报表模板关联的资源包。因此，报表标题通过从资源包中提取字符串值来显示。有关国际化的更多信息，请参见章节国际化。

计算器

计算器是 JasperReports 中的一个实体，它在报表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表中。此信息在报表填充时用于构建 net.sf.jasperreports.engine.fill.JRCalculator 类的实例。

Java 基于报表的编译器会动态生成和编译 Java 源文件。此生成的类是 JRCalculator 的子类，编译产生的字节码存储在 JasperReport 对象中。此字节码在报表填充时加载，并实例化结果类以获取表达式评估所需的计算器对象。

条件表达式

在定义变量表达式时，JasperReports 不支持 if-else 语句。相反，您可以使用三元运算符{cond} ? {statement 1} : {statement 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。

报表中条件表达式的示例

让我们修改现有的报表模板（章节报表设计）并为字段 country 添加一个条件表达式。修改后的报表模板（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>

报表填充的 Java 代码如下所示。文件C:\tools\jasperreports-5.0.1\test\src\com\tutorialspoint\JasperReportFill.java的内容如下：

package com.tutorialspoint;

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C:\tools\jasperreports-5.0.1\test\src\com\tutorialspoint\DataBean.java的内容如下：

package com.tutorialspoint;

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 列表中添加一条新的记录，其中 country 字段为空。文件C:\tools\jasperreports-5.0.1\test\src\com\tutorialspoint\DataBeanList.java的内容如下：

package com.tutorialspoint;

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;
   }
}

报表生成

我们将使用常规的 ANT 构建过程编译和执行上述文件。文件 build.xml（保存在目录 C:\tools\jasperreports-5.0.1\test 下）的内容如下所示。

导入文件 - baseBuild.xml 从章节环境设置中获取，应将其放置与 build.xml 相同的目录中。

<?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放置 build.xml 的目录。最后，执行命令ant -Dmain-class = com.tutorialspoint.JasperReportFill（viewFullReport 是默认目标），如下所示：

C:\tools\jasperreports-5.0.1\test>ant -Dmain-class=com.tutorialspoint.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
   https://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.tutorialspoint.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>

上述编译的结果是打开一个 JasperViewer 窗口，如下面的屏幕截图所示：

在这里，我们可以看到，对于最后一条记录，我们没有为字段 country 传递任何数据，“NO COUNTRY”正在打印。

打印页面