JasperReport深度探索：打造高效报表

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"Jasper.Report.Ultimate.Guide.pdf" 《JasperReports终极指南》是一本详细介绍JasperReport的权威书籍，作者是Teodor Danciu。JasperReport是一款功能强大且灵活性极高的报表生成工具，它能够将报表输出到各种不同的媒介，包括打印机、PDF、HTML以及XML文件。这本书旨在帮助用户深入理解和充分利用JasperReport的各项功能。在书中，作者首先介绍了JasperReports的基本概念，让读者对报表生成工具有一个初步的认识。接着，他提供了API概述，详细讲解了JasperReport的核心接口和类，这对于开发者来说是理解和使用JasperReport的基础。书中第三部分主要讲述了JasperReport的主要任务和处理流程。这包括： 1. **XML解析**：JasperReport的设计通常基于XML文件，这个过程涉及到解析这些设计文件以理解报表结构。 2. **编译报告设计**：将XML设计文件编译成可执行的JasperReport类，这是报表生成的前期准备。 3. **报告设计预览**：允许用户在实际填充数据之前查看报表的布局和样式。 4. **填充报告**：将数据源与报告设计结合，生成具体的报表内容。 5. **查看报告**：展示生成的报表，可以是网页、PDF或其他格式。 6. **打印报告**：支持直接从应用中打印报表，方便用户进行硬拷贝。 7. **导出报告**：提供多种导出选项，如PDF、HTML、Excel等，以便于在不同环境中使用或共享。 8. **对象加载和保存**：讨论如何在程序中加载和保存报表设计，确保报表模板的持久化。第四部分可能涉及更多关于报表设计和使用的高级话题，如自定义函数、图表、样式和格式设定，以及与其他Java Web技术（如Servlets、JSP）的集成。此外，书中可能还涵盖了如何处理大数据量、错误处理、性能优化等方面的内容。通过阅读这本书，读者不仅可以掌握JasperReport的基本用法，还能了解到如何根据具体需求定制报表，以及如何在实际项目中高效地运用JasperReport。对于从事Java Web开发，尤其是需要处理报表展示和分析的开发者来说，这是一本非常有价值的参考书。

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When compiling Java source files, the most important thing seems to be the classpath. If the Java

compiler does not find in the supplied classpath all the classes that are referenced by the source files it

tries to compile, the whole process fails and stops, the errors being displayed on the console.

The same happens also when JasperReports compiles the report expressions class. It is important then

to make sure we supply to the Java compiler at runtime the correct classpath for the compilation

process to succeed. For instance, we have to make sure that in the classpath we supply the custom

classes that we might use in the report expressions.

There is a default behavior for this aspect also. If no special classpath for compiling the report classes

is supplied, the engine will use the current JVM classpath returned by the system property

java.class.path. This default behavior can be overridden by putting the desired classpath in the

system property called

jasper.reports.compile.class.path.

You can see the jsp/compile.jsp and WEB-INF/classes/servlets/CompileServlet.java

files in the webapp sample provided, for the code snippet that makes use of this Java system properties

to override the default behavior of the JasperReports report compilation process.

Most of the time, compiling a report requires only a simple call to the JasperReports library like in the

following line of code:

dori.jasper.engine.JasperCompileManager.compileReport(myXmlFileName);

This call will produce the compiled report design and will store it in a file with the .jasper extension,

located in the same directory as the supplied XML report design file.

3.3 Report Design Preview

The JasperReports library is not shipped with an advanced GUI tool to help the design work. At this

time, there are at least 4 projects that try to provide such a tool.

However, the library contains a very helpful visual component that allows report creators to preview

the report designs as they build them.

The dori.jasper.view.JasperDesigner class is a simple Swing based Java application that can

load and display a report design either in its XML form or in the compiled form. Even if it is not a

complex GUI application, lacking advance functionality like the drag and dropping of the visual report

elements, it is very helpful instrument. All the supplied samples were created using this design viewer.

All the supplied samples have already prepared ANT tasks in their build.xml files that will launch

this design viewer for you to see the report designs.

In fact there are 2 ANT tasks for each sample report: viewDesign and viewDesignXML.

The first one loads the compiled report design that is normally found in the .jasper file. The second

one loads the XML report design, being the most useful since you can edit the XML file and push the

Reload button to immediately see the modification appearing on the screen.

If you have the ANT build tool installed on your system, in order to preview a sample report design,

you simply go to the desired sample directory and launch from the command line something like this:

>ant viewDesignXML

>ant viewDesign

In case you do not have ANT installed and you don't want to get it (you'll miss all the fun), here's the

complete command line that will launch the design viewer to preview one of the sample XML report

designs. We assume that you have a copy of the entire JasperReports source tree on your system

(Windows command line syntax):

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>java -classpath ./;../../../lib/commons-digester.jar;

../../../lib/commons-beanutils.jar;../../../lib/commons-collections.jar;

../../../lib/xerces.jar;../../../lib/jasperreports.jar

-Dorg.xml.sax.driver=org.apache.xerces.parsers.SAXParser

dori.jasper.view.JasperDesignViewer -XML -FFirstJasper.xml

By launching this command line, you should be able to see this window:

- figure 4 -

3.4 Filling Reports

The report filling process is the most important of all the JasperReports library functionality. It

represents the main objective for this piece of software, as it is the process that manipulates sets of data

in order to produce high quality documents, just like any reporting tool is supposed to do.

There are tree things that should be supplied to the report filling process as input:

· report design (report template);

· parameters;

· data source.

The output is always a single, final document that is ready to be viewed, printed or exported to other

formats.

We have already seen that in order to fill a report, we are going to use the

dori.jasper.engine.JasperFillManager class. This class has various methods that allow us to

fill report designs that are located on disk, come from input streams or are supplied directly as in-

memory

dori.jasper.engine.JasperReport objects.

The output produced always corresponds to the type of the input received. That is, when receiving a

file name for the report design, the generated report will be also placed in a file on disk. When the

report design is read from an input stream, the generated report will be written to an output stream and

so forth.

It might be that those various utility methods for filling the reports are not sufficient for a particular

application, who for example would want to load report designs as resources from classpath and output

the generated documents to files on disk, at a certain location.

In such cases, the developers should consider loading the report design objects before passing them to

the report filling routines, using the

dori.jasper.engine.util.JRLoader utility class. This way,

they could retrieve some report design properties such as the report name, so they can construct the

name of the resulting document, to place at the desired disk location.

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There are a lot of report filling scenarios that could be imagined in a real world application, and the

report filling manager class only tries to cover a portion of them, considered to be used more often. But

it should be no problem for anybody who might want to customize the report-filling process using the

library's basic functionality, as suggested above.

The report parameter values are supplied always packed in a java.util.Map object, which has the

parameter names as its keys.

As for the third thing that the report filling process expects to receive, the data source, there are two

different scenarios.

Normally, the engine works with an instance of the dori.jasper.engine.JRDataSource interface,

from which it extracts the data when filling the report.

And the façade class dori.jasper.engine.JasperFillManager has a full set of methods that

receive a

dori.jasper.engine.JRDataSource object as the data source of the report that is going

to be filled.

But there is another set of report filling methods in this manager class that receive a

java.sql.Connection object as a parameters, instead of expected data source object.

This is because most of the time reports are generated using data that comes from tables found in

relational databases.

Users have the possibility to specify the SQL query needed to retrieve the report data from the

database, in the report design itself. At runtime, the only thing the engine would need would be a JDBC

connection object to use in order to connect to the desired relational database, execute the SQL query

and retrieve the report data.

Behind the scenes, the engine will still use a special dori.jasper.engine.JRDataSource object,

but this is preformed transparently for the calling program.

There are at least 4 sample applications provided with the project, which fill the reports using data from

an also supplied HSQL database server. Those are jasper, query, scriptlet and subreport samples. To

run them, you have to start the HSQL database server first, by going to the

/demo/hsqldb directory of

the JasperReports project and launching this command:

>ant

>ant runServer

Note that you have to have ANT build tool installed on your system for you to launch the server in such

as simple manner. Otherwise you could still launch it like this:

>java -classpath ./;../../lib/hsqldb.jar org.hsqldb.Server

Here's a simple code snippet taken from the query sample that shows how to fill a report:

//Preparing parameters

Map parameters = new HashMap();

parameters.put("ReportTitle", "Address Report");

parameters.put("FilterClause", "'Boston', 'Chicago', 'Oslo'");

parameters.put("OrderClause", "City");

//Invoking the filling process

JasperFillManager.fillReportToFile(fileName, parameters, getConnection());

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JasperReport深度探索：打造高效报表

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