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All unexpected exceptions resulting in a possibly corrupted state of the ReportDesigner should be added to the UncaughtExcfeptionsModel. This usually leads in a red blinking warning message on the ReportDialog.
org.pentaho.reportdesigner.lib.client.util.FontUtils
FontUtils can be used to derive fonts. StyleContext is internally used to prevent a bug where Japanese characters of a derived font didn't render anymore. Additionally StyleContext uses a simple cache that might speed up the derive operation a little bit.
org.pentaho.reportdesigner.lib.client.util.IOUtil
IOUtil is used to clase streams (always close streams accessing native resources).