報表表示式

報表表示式是 JasperReports 的強大功能，它允許我們在報表上顯示計算出的資料。計算出的資料不是靜態資料，也不是作為報表引數或資料來源欄位專門傳遞的資料。報表表示式是透過組合報表引數、欄位和靜態資料構建的。預設情況下，Java 語言用於編寫報表表示式。JasperReports 編譯器支援其他用於報表表示式的指令碼語言，如 Groovy 指令碼語言、JavaScript 或 BeanShell 指令碼。

本章將向您解釋 - 報表表示式是如何工作的，假設它們僅使用 Java 語言編寫。在 JRXML 報表模板中，有幾個元素定義了表示式，如下所示：

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

表示式宣告

基本上，所有報表表示式都是 Java 表示式，可以引用報表欄位、報表變數和報表引數。

表示式中的欄位引用

要在表示式中使用報表欄位引用，必須將欄位名稱放在$F{和}字元序列之間，如下所示：

<textfieldexpression>
   $F{Name}
</textfieldexpression>

以下是我們現有 JRXML 檔案（章節報表設計）中的一段程式碼：

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

表示式中的變數引用

要在表示式中引用變數，必須將變數名稱放在$V{和}之間，如下例所示：

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

表示式中的引數引用

要在表示式中引用引數，應將引數名稱放在$P{和}之間，如下例所示：

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

以下是我們現有 JRXML 檔案中的一段程式碼，它演示了在表示式中引用引數。（來自章節報表設計的 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，引數、欄位和變數引用實際上是真實的 Java 物件。瞭解報表模板中引數、欄位或變數宣告的類，我們甚至可以在表示式中呼叫這些物件引用的方法。

以下示例顯示了 - 如何從 java.lang.String 報表欄位“Name”中提取並顯示第一個字母：

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

表示式中的資源包引用

要在表示式中引用資源，應將鍵放在$R{和}之間，如下例所示：

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

根據執行時提供的區域設定和report.title鍵，載入與報表模板關聯的資源包。因此，報表標題透過從資源包中提取字串值來顯示。有關國際化的更多資訊，請參見章節國際化。

計算器

計算器是 JasperReports 中的一個實體，它在報表填充時評估表示式並遞增變數或資料集。在編譯過程中，編譯器會生成資訊並將其儲存在編譯報表中。此資訊在報表填充時用於構建 net.sf.jasperreports.engine.fill.JRCalculator 類的例項。

Java 基於報表的編譯器會動態生成和編譯 Java 原始檔。此生成的類是 JRCalculator 的子類，編譯產生的位元組碼儲存在 JasperReport 物件中。此位元組碼在報表填充時載入，並例項化結果類以獲取表示式評估所需的計算器物件。

條件表示式

在定義變量表達式時，JasperReports 不支援 if-else 語句。相反，您可以使用三元運算子{cond} ? {statement 1} : {statement 2}。此運算子可以巢狀在 Java 表示式中，以根據多個條件獲得所需的輸出。

報表中條件表示式的示例

讓我們修改現有的報表模板（章節報表設計）併為欄位 country 新增一個條件表示式。修改後的報表模板（jasper_report_template.jrxml）如下所示。將其儲存到 C:\tools\jasperreports-5.0.1\test 目錄：

<?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>

報表填充的 Java 程式碼如下所示。檔案C:\tools\jasperreports-5.0.1\test\src\com\tutorialspoint\JasperReportFill.java的內容如下：

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 檔案C:\tools\jasperreports-5.0.1\test\src\com\tutorialspoint\DataBean.java的內容如下：

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;
   }
}

我們將在 Java bean 列表中新增一條新的記錄，其中 country 欄位為空。檔案C:\tools\jasperreports-5.0.1\test\src\com\tutorialspoint\DataBeanList.java的內容如下：

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;
   }
}

報表生成

我們將使用常規的 ANT 構建過程編譯和執行上述檔案。檔案 build.xml（儲存在目錄 C:\tools\jasperreports-5.0.1\test 下）的內容如下所示。

匯入檔案 - baseBuild.xml 從章節環境設定中獲取，應將其放置與 build.xml 相同的目錄中。

<?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>

接下來，讓我們開啟命令列視窗並轉到放置 build.xml 的目錄。最後，執行命令ant -Dmain-class = com.tutorialspoint.JasperReportFill（viewFullReport 是預設目標），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
   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>

上述編譯的結果是開啟一個 JasperViewer 視窗，如下面的螢幕截圖所示：

在這裡，我們可以看到，對於最後一條記錄，我們沒有為欄位 country 傳遞任何資料，“NO COUNTRY”正在列印。

列印頁面