我们在前面的章节中已经看到，报告中显示的数据通常是从报告参数和报告字段中提取的.可以使用报告变量及其表达式处理此数据.有些情况下，使用报表表达式或变量无法轻松实现复杂功能.这样的示例可能是复杂的字符串操作，构建映射，或内存中的对象列表或使用第三方Java API操作日期.对于这种情况，JasperReports通过 Scriptlets 为我们提供了一种简单而强大的方法.
Scriptlet是每次报告时执行的Java代码序列事件发生.报告变量的值可以通过scriptlet受到影响.
我们可以用两种方式声明一个scriptlet :
使用< scriptlet >元件.此元素具有 name 属性和 class 属性. 类属性应指定类的名称，该类扩展 JRAbstractScriptlet 类.该类必须在报告填充时在类路径中可用，并且必须具有空构造函数，以便引擎可以动态实例化它.
使用属性 scriptletClass 元素< jasperReport >，在报告模板(JRXML)中.通过使用scriptlet的完全限定名称(包括整个包名称)设置此属性，我们指示我们要使用scriptlet.使用此属性创建的scriptlet实例的行为类似于scriptlet列表中的第一个scriptlet，并具有
预定义名称REPORT.
scriptlet是一个java类，它必须扩展以下任一类 :
net.sf.jasperreports.engine.JRAbstractScriptlet : 此类包含许多必须在每个实现中重写的抽象方法. JasperReports会在适当的时候自动调用这些方法.开发人员必须实现所有抽象方法.
net.sf.jasperreports.engine.JRDefaultScriptlet : 此类包含JRAbstractScriptlet中每个方法的默认空实现.开发人员只需要为他/她的项目实现他/她所需的方法.
下表列出了上述类中的方法.在报告填写阶段，报告引擎将在适当的时间调用这些方法.
| S.NO | 方法和描述 |
|---|---|
| 1 | public void beforeReportInit() 在报告初始化之前调用. |
| 2 | public void afterReportInit( ) 报告初始化后调用. |
| 3 | public void beforePageInit() 在每个页面初始化之前调用. |
| 4 | public void afterPageInit() 在每个页面初始化后调用. |
| 5 | public void beforeColumnInit() 在每列初始化之前调用. |
| 6 | public void afterColumnInit() 在每列初始化后调用. |
| 7 | public void beforeGroupInit(String groupName ) 在参数中指定的组初始化之前调用. |
| 8 | public void afterGroupInit(String groupName) 之后调用初始化参数中指定的组. |
| 9 | public void beforeDetailEval() 在评估报告的详细信息部分中的每条记录之前调用. |
| 10 | public void afterDetailEval() 评估报告详细信息部分中的每条记录后调用. |
每个报告可以指定任意数量的scriptlet.如果没有为报告指定scriptlet，引擎仍然会创建一个JRDefaultScriptlet实例并使用内置的REPORT_SCRIPTLET参数进行注册.
我们可以添加我们需要的任何其他方法小脚本.报告可以使用内置参数REPORT_SCRIPTLET来调用这些方法.
我们可以将scriptlet以另一种方式关联到报告，这是通过全局声明scriptlet.这使得scriptlet适用于在给定JasperReports部署中填充的所有报告.这可以通过将scriptlet作为扩展添加到JasperReports来实现. scriptlet扩展点由 net.sf.jasperreports.engine.scriptlets.ScriptletFactory 接口表示. JasperReports将在运行时通过扩展加载所有可用的scriptlet工厂.然后，它会向每个人询问他们想要应用于正在运行的当前报告的scriptlet实例列表.在询问scriptlet实例列表时，引擎会提供一些工厂可以使用的上下文信息，以确定哪些scriptlet实际应用于当前报告.
调控器只是全局scriptlet的扩展，使我们能够解决报表引擎在运行时进入无限循环的问题，同时生成报表.在设计时无法检测到无效的报告模板，因为大多数情况下，进入无限循环的条件取决于在运行时送入引擎的实际数据.报告总督帮助决定某个报告是否已进入无限循环，他们可以阻止它.这可以防止运行报告的计算机耗尽资源.
JasperReports有两个简单的报告管理器，可以根据指定的最大页数或指定的超时间隔停止报告执行.它们是 :
net.sf.jasperreports.governors.MaxPagesGovernor : 这是一个全局scriptlet，它正在寻找两个配置属性来决定它是否适用于当前正在运行的报表.配置属性为 :
net.sf.jasperreports.governor.max.pages.enabled = [true | false ]
net.sf.jasperreports.governor.max.pages = [integer]
net.sf.jasperreports.governors.TimeoutGovernor : 这也是一个全局scriptlet，它正在寻找以下两个配置属性来决定它是否适用.
配置属性是 :
net.sf.jasperreports.governor.timeout.enabled = [true | false]
net.sf.jasperreports.governor.timeout = [毫秒]
两个调控器的属性可以在jasperreports.properties文件中全局设置，也可以在报表级别设置为自定义报表属性.这很有用，因为不同的报告可能有不同的估计大小或超时限制，也因为您可能需要为所有报告启用调控器，而为某些报告启用它，反之亦然.
让我们编写一个scriptlet类( MyScriptlet ).文件C:\tools \jasperreports-5.0.1 \test\src\com\it1352\MyScriptlet.java的内容如下 :
package com.it1352;
import net.sf.jasperreports.engine.JRDefaultScriptlet;
import net.sf.jasperreports.engine.JRScriptletException;
public class MyScriptlet extends JRDefaultScriptlet {
public void afterReportInit() throws JRScriptletException{
System.out.println("call afterReportInit()");
// this.setVariableValue("AllCountries", sbuffer.toString());
this.setVariableValue("someVar", new String("This variable value
was modified by the scriptlet."));
}
public String hello() throws JRScriptletException {
return "Hello! I'm the report's scriptlet object.";
}
}上述scriptlet类的详细信息如下 :
在 afterReportInit 方法中，我们将值设置为变量"someVar". setVariableValue("someVar"，new String("此变量值由scriptlet修改.")).
在课程结束时，额外已经定义了名为'hello'的方法.这是一个可以添加到实际返回值的Scriptlet的方法示例，而不是设置变量.
下一步，我们将在现有的报告模板中添加scriptlet类引用(章节报告设计).修订后的报告模板(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"
scriptletClass = "com.IT屋.MyScriptlet">
<style name = "alternateStyle" fontName = "Arial" forecolor = "red">
<conditionalStyle>
<conditionExpression>
<![CDATA[new Boolean($V{countNumber}.intValue() % 2 == 0)]]>
</conditionExpression>
<style forecolor = "blue" isBold = "true"/>
</conditionalStyle>
</style>
<parameter name = "ReportTitle" class = "java.lang.String"/>
<parameter name = "Author" class = "java.lang.String"/>
<queryString>
<![CDATA[]]>
</queryString>
<field name = "country" class = "java.lang.String">
<fieldDescription>
<![CDATA[country]]>
</fieldDescription>
</field>
<field name = "name" class = "java.lang.String">
<fieldDescription>
<![CDATA[name]]>
</fieldDescription>
</field>
<variable name = "countNumber" class = "java.lang.Integer"
calculation = "Count">
<variableExpression><
![CDATA[Boolean.TRUE]]>
</variableExpression>
</variable>
<variable name = "someVar" class = "java.lang.String">
<initialValueExpression>
<![CDATA["This is the initial variable value."]]>
</initialValueExpression>
</variable>
<title>
<band height = "100">
<line>
<reportElement x = "0" y = "0" width = "515" height = "1"/>
</line>
<textField isBlankWhenNull = "true" bookmarkLevel = "1">
<reportElement x = "0" y = "10" width = "515" height = "30"/>
<textElement textAlignment = "Center">
<font size = "22"/>
</textElement>
<textFieldExpression class = "java.lang.String">
<![CDATA[$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[$P{Author}]]>
</textFieldExpression>
</textField>
<textField isBlankWhenNull = "true">
<reportElement x = "0" y = "50" width = "515"
height = "30" forecolor = "#993300"/>
<textElement textAlignment = "Center">
<font size = "10"/>
</textElement>
<textFieldExpression class = "java.lang.String">
<![CDATA[$V{someVar}]]>
</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 style = "alternateStyle" x="414" y = "0"
width = "121" height = "15" />
<textElement textAlignment = "Center" verticalAlignment = "Middle">
<font size = "9" />
</textElement>
<textFieldExpression class = "java.lang.String">
<![CDATA[$F{country}]]>
</textFieldExpression>
</textField>
<textField>
<reportElement x = "0" y = "0" width = "136" height = "15" />
<textElement textAlignment = "Center" verticalAlignment = "Middle" />
<textFieldExpression class = "java.lang.String">
<![CDATA[$F{name}]]>
</textFieldExpression>
</textField>
</band>
</detail>
<summary>
<band height = "45">
<textField isStretchWithOverflow = "true">
<reportElement x = "0" y = "10" width = "515" height = "15" />
<textElement textAlignment = "Center"/>
<textFieldExpression class = "java.lang.String">
<![CDATA["There are " + String.valueOf($V{REPORT_COUNT}) +
" records on this report."]]>
</textFieldExpression>
</textField>
<textField isStretchWithOverflow = "true">
<reportElement positionType = "Float" x = "0" y = "30" width = "515"
height = "15" forecolor = "# 993300" />
<textElement textAlignment = "Center">
<font size = "10"/>
</textElement>
<textFieldExpression class = "java.lang.String">
<![CDATA[$P{REPORT_SCRIPTLET}.hello()]]>
</textFieldExpression>
</textField>
</band>
</summary>
</jasperReport>修订后的报告模板的详细信息在下面和下面给出;
我们在< jasperReport>的属性 scriptletClass 中引用了MyScriptlet类.元件.
Scriptlets只能访问，但不能修改报告字段和参数.但是，scriptlet可以修改报表变量值.这可以通过调用setVariableValue()方法来完成.此方法在JRAbstractScriptlet类中定义，该类始终是任何scriptlet的父类.在这里，我们定义了一个变量 someVar ，它将被MyScriptlet修改为具有值该值由scriptlet修改.
上述报告模板在摘要带中有一个方法调用，说明如何编写新方法(在scriptlet中)并在报告模板中使用它们. ( $ P {REPORT_SCRIPTLET} .hello())
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;
公共类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;
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选取的，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${file.name}.JRprint" />
<classpath refid = "classpath" />
</java>
</target>
<target name = "compilereportdesing" description = "Compiles the JXML file and
produces the .jasper file.">
<taskdef name = "jrc" classname = "net.sf.jasperreports.ant.JRAntCompileTask">
<classpath refid = "classpath" />
</taskdef>
<jrc destdir = ".">
<src>
<fileset dir = ".">
<include name = "*.jrxml" />
</fileset>
</src>
<classpath refid = "classpath" />
</jrc>
</target>
</project>接下来，让我们打开命令行窗口并转到build.xml所在的目录.最后，执行命令 ant -Dmain-class = com.it1352.JasperReportFill (viewFullReport是默认目标)为 :
<?xml version = "1.0" encoding = "UTF-8"?>
<project name = "JasperReportTest" default = "viewFillReport" basedir = ".">
<import file = "baseBuild.xml" />
<target name = "viewFillReport" depends = "compile,compilereportdesing,run"
description = "Launches the report viewer to preview
the report stored in the .JRprint file.">
<java classname = "net.sf.jasperreports.view.JasperViewer" fork = "true">
<arg value = "-F${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由于上面的编译，JasperViewer窗口打开up如下面给出的屏幕所示 :
这里我们看到两条消息显示在MyScriptlet类和减号中;
在标题部分 : 此变量值由scriptlet修改
在底部和底部; 您好！我是报告的scriptlet对象.
