报告表达

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的数据。计算数据是非静态数据且不专门作为报表参数或数据源字段传递的数据。报表表达式是通过组合报表参数、字段和静态数据而构建的。默认使用Java语言编写报表表达式。JasperReports 编译器支持报表表达式的其他脚本语言，例如 Groovy 脚本语言、JavaScript 或 BeanShell 脚本。

本章将向您解释 - 假设报表表达式仅使用 Java 语言编写，那么它们是如何工作的。在 JRXML 报告模板中，有几个元素将表达式定义为 -

  • <变量表达式>
  • <初始值表达式>
  • <组表达式>
  • <打印时表达式>
  • <图像表达式>
  • <文本字段表达式>

表达式声明

基本上，所有的报表表达式都是Java表达式，它可以引用报表字段、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告字段引用，字段的名称必须放在$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（报告设计一章） -

<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，我们必须将变量的名称放在$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，参数的名称应放在$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，它演示了表达式中参数的引用。（JRXML 来自“报告设计”一章）-

<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>

正如您在上面看到的，参数、字段和变量引用实际上是真正的 Java 对象。通过报表模板中的参数、字段或变量声明了解它们的类，我们甚至可以在表达式中的这些对象引用上调用方法。

以下示例显示 - 如何从 java.lang.String 报告字段“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，键应放在$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字符串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

计算器是 JasperReports 中的一个实体，它在报告填充时计算表达式并递增变量或数据集。在编译过程中，编译器产生信息并将其存储在编译报告中。此信息在报告填充期间用于构建 net.sf.jasperreports.engine.fill.JRCalculator 类的实例。

Java 源文件由基于 Java 的报告编译器即时生成和编译。这个生成的类是JRCalculator的子类，编译它产生的字节码存储在JasperReport对象中。该字节码在报告填充时加载，并实例化生成的类以获得表达式求值所需的计算器对象。

条件表达式

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} ? {语句1}：{语句2}。该运算符可以嵌套在 Java 表达式中，以根据多个条件获得所需的输出。

报告中的条件表达式示例

让我们修改现有的报告模板（报告设计章节）并为字段国家/地区添加条件表达式。修改后的报告模板（jasper_report_template.jrxml）如下。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>

报表填写的java代码如下。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 列表中添加一条新记录，其中国家/地区字段为空。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;
   }
}

报告生成

我们将使用常规 ANT 构建过程来编译并执行上述文件。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 是从“环境设置”一章中选取的，并且应放置在与 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，我们打开命令行窗口并进入build.xml所在的目录。最后，执行命令ant -Dmain-class = com.tutorialspoint.JasperReportFill（viewFullReport 是默认目标）如下：

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
   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.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>

作为上述编译的结果，JasperViewer 窗口将打开，如下面给出的屏幕所示 -

Jasper 报表表达式示例

在这里，我们可以看到，对于最后一条记录，我们没有传递字段国家/地区的任何数据，正在打印“NO COUNTRY”。