PDF Export Fails with 'Could not initialize class com.sun.imageio.plugins.jpeg.JPEGImageReader' Error

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*Except Fisheye and Crucible

Summary

Space PDF Export Fails with 'Could not initialize class com.sun.imageio.plugins.jpeg.JPEGImageReader' Error

Environment

Confluence Server and Data Center.

Diagnosis

When trying to export a space to PDF, the export hangs and never completes.
Looking at the atlassian-confluence.log, we can see the following:

2020-10-30 12:39:02,450 ERROR [Long running task: PDF Space Export] [confluence.util.longrunning.ConfluenceAbstractLongRunningTask] run Long running task "PDF Space Export" failed to run.
 -- url: /spaces/flyingpdf/doflyingpdf.action | referer: https://localhost/spaces/flyingpdf/flyingpdf.action?key=TEST | traceId: fe4660335bd8ba04 | userName: username | action: doflyingpdf
java.lang.NoClassDefFoundError: Could not initialize class com.sun.imageio.plugins.jpeg.JPEGImageReader
	at com.sun.imageio.plugins.jpeg.JPEGImageReaderSpi.createReaderInstance(JPEGImageReaderSpi.java:85)
	at com.twelvemonkeys.imageio.plugins.jpeg.JPEGImageReaderSpi.createReaderInstance(JPEGImageReaderSpi.java:110)
	at javax.imageio.spi.ImageReaderSpi.createReaderInstance(ImageReaderSpi.java:320)
	at javax.imageio.ImageIO$ImageReaderIterator.next(ImageIO.java:529)
	at javax.imageio.ImageIO$ImageReaderIterator.next(ImageIO.java:513)
	at com.atlassian.confluence.extra.flyingpdf.impl.LightITextFSImage.updateMeasurements(LightITextFSImage.java:76)

Cause

This error happens when Java is updated without shutting down Confluence first, making the Confluence process point to a Java path that no longer exists, and triggering the NoClassDefFoundError.

Solution

Restart Confluence.

Atlassian Support