|
Images in JasperReports
Below is an image.
Images are the most complex graphic objects in a report. Just as for text field elements,
their content is dynamically evaluated at runtime, using a report expression. The process of
image rendering depends on a set of attributes and expressions available for the <image/> element.
Image Attributes
-
scaleImage - indicates how should be rendered the image when its actual size does not fit the size of the image report element.
This is because in a lot of situations images are loaded at runtime and there is no way to know their exact size when creating the report template.
Possible values for this attribute are:
-
Clip - if the actual image is larger than the image element size, it will be cut off so that it keeps its original resolution,
and only the region that fits the specified size will be displayed.
-
FillFrame - if the dimensions of the actual image do not fit those
specified for the image element that displays it, the image is forced to obey them
and stretch itself so that it fits in the designated output area. It will be deformed if
necessary.
-
RetainShape - if the actual image does not fit into the image
element, it can be adapted to those dimensions while keeping its original undeformed proportions.
-
RealHeight - the image can be stretched vertically to
match the actual image height, while preserving the declared width of the image element.
-
RealSize - the image can be stretched vertically to
match the actual image height, while adjusting the width of the image element to match the actual image width.
- If the scale type for the image is
Clip or RetainShape and the actual image is smaller
than its defined size in the report template or does not have the same proportions, the
image might not occupy all the space allocated to it in the report template. In these conditions the image can be both
horizontally and vertically aligned within its report element. Two attributes are responsible for the image alignment:
-
hAlign - specifies the horizontal alignment. Possible values are: Left, Center, Right.
-
vAlign - specifies the vertical alignment. Possible values are: Top, Middle, Bottom.
-
isUsingCache - flag that indicates if an image should be loaded each time it gets displayed in a report, or
if it should be loaded only once and then stored in a memory cache for better performance. For images with static content applying the
caching mechanism is strongly recommended. When one set the isUsingCache attribute to
true, the reporting engine will try to recognize previously loaded images using their specified source.
This caching functionality is available for image elements whose expressions return
objects of any type as the image source. The isUsingCache flag is set to true by
default for images having java.lang.String expressions and to false for all other
types.
-
isLazy - flag that specifies whether the image should be loaded and processed during report filling or
during exporting, in case that the image is not available at fill time. By default this flag is set to false.
When it is set to true, an image path String is stored at fill time instead of the image itself, and during the
exporting process the image will be loaded from the location read from this path String. For example, this sample contains an
image element pointing to the JasperReports logo, which is lazy loaded from the project’s web site.
-
onErrorType - if an image is unavailable when the engine tries to load it, some kind of output should be provided
instead. The onErrorType attribute specifies this output. Possible values are:
-
Error - an exception is thrown if the engine cannot load the image.
-
Blank - any image-loading exception is ignored and nothing will appear in the generated document.
-
Icon - the engine will put a small specific icon in the document to indicate that the actual image is missing.
-
evaluationTime - specify the moment when the image expression gets evaluated. Possible values are:
-
Now - the image expression is evaluated when the current band is filled.
-
Report - the image expression is evaluated when the end of the report is reached.
-
Page - the image expression is evaluated when the end of the current page is reached.
-
Column - the image expression is evaluated when the end of the current column is reached.
-
Group - the image expression is evaluated when the group specified by the evaluationGroup attribute changes.
-
Auto - each variable participating in the image expression is evaluated at a time corresponding to its reset type.
-
evaluationGroup - the group involved in the image evaluation process when the evaluationTime attribute is set to Group.
Image Expression
The value returned by the image expression is the source for the image to be displayed.
The image expression is introduced by the <imageExpression/> element and can return
values from only the limited range of classes listed following:
-
java.lang.String
-
java.io.File
-
java.net.URL
-
java.io.InputStream
-
java.awt.Image
-
net.sf.jasperreports.engine.JRRenderable
Image Hyperlinks
In JasperReports image elements provide hyperlink support. All available hyperlink expressions are allowed to be part of an <image/> element.
See also the hyperlink sample.
Image Examples
This reports/ImagesReport.jrxml report template contains a series of image examples, having a specific combination of the attributes above.
The first image in the report is loaded from the http://jasperreports.sourceforge.net web site at export time.
<image scaleImage="Clip" onErrorType="Icon" isLazy="true">
<reportElement x="0" y="0" width="150" height="40"/>
<imageExpression class="java.lang.String"><![CDATA["http://jasperreports.sourceforge.net/jasperreports.png"]]></imageExpression>
</image>
The last image in the report template is loaded from the src/dukesign.jpg file in this sample and is scaled to its real height.
The image expression's class is missing, therefore it is assumed to be java.lang.String. The image style is imageBox,
a report style defined for images with visible border lines.
<image scaleImage="RealHeight">
<reportElement x="0" y="0" width="100" height="40" style="imageBox"/>
<imageExpression><![CDATA["dukesign.jpg"]]></imageExpression>
</image>
Running the Sample
Running the sample requires the Apache Ant library. Make sure that ant is already installed on your system (version 1.5 or later).
In a command prompt/terminal window set the current folder to demo/samples/images within the JasperReports source project and run the > ant test view command.
It will generate all supported document types containing the sample report in the demo/samples/images/build/reports directory.
Then the report will open in the JasperReports internal viewer.
|
