jasperreport生成pdf_jasperreport 导出excel_jasperreport json(63)

The so-called subreport expression is introduced by the <subreportExpression> element and can

return values from the following classes:

java.lang.String

java.io.File

java.net.URL

java.io.InputStream

dori.jasper.engine.JasperReport

When the subreport expression returns a java.lang.String value, the engine will try to

see whether the value represents an URL from which to load the subreport design object. If

it is not a valid URL representation, it will try to locate a file on disk and load the subreport

design from it, assuming that the value represents a file name. If no file is found, it will

finally assume that the string value represents the location of a classpath resource and will

try to load the subreport design from there. Only if all those fail, an exception will be

thrown.

If the image expression class is not specified using the class attribute, it is assumed to be

java.lang.String, by default.

Caching Subreports

A subreport element can load different subreport designs with every evaluation, giving you great

flexibility in shaping you documents.

However, most of the time, the subreport elements on a report are in fact static and their source do not

necessarily change with every new evaluation of the subreport expression. In the majority of cases, the

subreport designs are loaded from fixed locations: files on disk or static URLs.

If the same subreport design is filled multiple times on a report, there is no point on loading the

subreport design object from the source file every time we have to fill it with data.

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