JasperReports 报表字段Field
1 JasperReports 报表字段声明
报表字段是元素，表示数据源和报表模板之间的数据映射。可以在报表表达式中组合字段以获得所需的输出。报告模板可以包含零个或多个 <field> 元素。声明报表字段时，数据源应提供与报表模板中定义的所有字段对应的数据。
参数声明如下：
<field name = "FieldName" class = "java.lang.String"/>
name属性
<field> 元素的name属性是必须的。它按名称引用报表表达式中的字段。
class属性
class属性指定的字段值类的名称。它的默认值是java.lang.String。这可以更改为运行时可用的任何类。无论报表字段的类型如何，引擎都会在使用 $F{} 标记的报告表达式中进行转换，因此无需手动转换。
2 JasperReports <fieldDescription>元素
<fieldDescription> 元素是一个可选元素。这在实现自定义数据源时非常有用。例如，我们可以存储一个键或一些信息，通过这些信息我们可以在运行时从自定义数据源中检索字段的值。通过使用 <fieldDescription> 元素而不是字段名称，您可以在从数据源检索字段值时轻松克服字段命名约定的限制。
以下是我们现有的 JRXML 文件（JasperReports 模板设计章节）中的一段代码。在这里，我们可以看到name、class和fieldDescription元素的用法。
<field name = "country" class = "java.lang.String">
<fieldDescription><![CDATA[country]]></fieldDescription>
</field>
<field name = "name" class = "java.lang.String">
<fieldDescription><![CDATA[name]]></fieldDescription>
</field>
3 JasperReports 报表字段的排序
在需要数据排序而数据源实现不支持的时候（例如CSV 数据源），JasperReports 支持基于内存字段的数据源排序。可以使用报告模板中的一个或多个 <sortField> 元素进行排序。
如果至少指定了一个排序字段，则在报表填充过程中，数据源将传递给JRSortableDataSource实例。这反过来，从数据源中获取所有记录，根据指定的字段在内存中进行排序，并替换原始数据源。
排序字段名称应与报告字段名称相同。用于排序的字段应具有实现 java.util.Comparable 的类型。对除java.lang.String 类型的字段外的所有字段执行自然顺序排序（对于String 类型，使用与报表填充区域设置相对应的collator）。当指定了多个排序字段时，将使用字段作为排序键，按照它们在报告模板中出现的顺序进行排序。以下示例演示了排序功能。
4 JasperReports 报表字段排序的示例
本案例中，我们将 < sortField > 元素添加到我们现有的报表模板（JasperReports 模板设计章节）。让我们按降序对字段country进行排序。
项目结构如下：
pom.xml文件
<dependencies>
<!-- https://mvnrepository.com/artifact/net.sf.jasperreports/jasperreports -->
<dependency>
<groupId>net.sf.jasperreports</groupId>
<artifactId>jasperreports</artifactId>
<version>6.17.0</version>
</dependency>
<dependency>
<groupId>org.codehaus.groovy</groupId>
<artifactId>groovy-all</artifactId>
<version>2.4.7</version>
</dependency>
<dependency>
<groupId>org.apache.poi</groupId>
<artifactId>poi</artifactId>
<version>3.17</version>
</dependency>
</dependencies>
DataBean实体类：
package com.yiidian;
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;
}
}
DataBeanList类：
package com.yiidian;
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"));
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;
}
}
jasper_report_template.jrxml模板文件：
<?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}]]>
</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>
先编译报表文件：
package com.yiidian;
import net.sf.jasperreports.engine.*;
import net.sf.jasperreports.view.JasperViewer;
public class JasperReportFill {
public static void main(String[] args) {
String filePath = "D:/idea_codes/jasper_reports/jasper_report_template.jrxml";
try {
JasperCompileManager.compileReportToFile(filePath,"d:/jasper_report_template.jasper");
System.out.println("编译成功");
} catch (JRException e) {
e.printStackTrace();
}
}
}
编译后在D:/盘根目录下生成jasper_report_template.jasper文件，然后再填充数据：
package com.yiidian;
import net.sf.jasperreports.engine.*;
import net.sf.jasperreports.engine.data.JRBeanCollectionDataSource;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
public class JasperReportFill {
public static void main(String[] args) {
String sourceFileName = "d:/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();
}
}
}
填充数据完毕后，在D:/盘根目录下生成jasper_report_template.jrprint文件，最后使用预览程序预览：
package com.yiidian;
import net.sf.jasperreports.engine.*;
import net.sf.jasperreports.view.JasperViewer;
public class JasperReportFill {
public static void main(String[] args) {
String filePath = "D:/jasper_report_template.jrprint";
try {
JasperViewer.viewReport(filePath,false);
} catch (JRException e) {
e.printStackTrace();
}
}
}
最后输出结果如下：
从效果我们看到，国家名称按字母顺序降序排列。
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