flowable/flowable-engine · error · FlowableImageException

Error while generating process image

Error message

Error while generating process image

What it means

DefaultProcessDiagramCanvas.generateImage() writes the rendered BufferedImage via ImageIO.write to a ByteArrayOutputStream. If the underlying ImageIO write fails with an IOException (unsupported image type string, missing image writer, IO problem), it is wrapped in FlowableImageException with this message.

Solutions

1. Verify the imageType is one of the formats supported by ImageIO (e.g. "png", "gif", "jpg") on the target JVM
2. Inspect the wrapped cause exception for the real IOException
3. Ensure the JDK/JRE includes standard image writers (not a minimal/headless-distilled JRE without codecs)
4. Call ImageIO.getWriterFormatNames() at startup to confirm supported formats

Example fix

// before
InputStream is = canvas.generateImage("jpeg2000"); // no writer registered
// after
InputStream is = canvas.generateImage("png");

boolean supported = java.util.Arrays.asList(javax.imageio.ImageIO.getWriterFormatNames())
        .contains(imageType.toLowerCase());
if (!supported) throw new IllegalArgumentException("Unsupported image type: " + imageType);

try {
    InputStream is = canvas.generateImage(imageType);
} catch (FlowableImageException e) {
    log.error("Image generation failed for type " + imageType, e.getCause());
}

When it happens

Trigger: Passing an imageType string with no registered ImageIO writer (e.g. a typo like "jpeg " or a type unsupported on the JRE); an IOException inside ImageIO.write while serializing the diagram.

Common situations: Using an exotic image format not supported by the headless JVM; running in a stripped-down container JDK without the standard image codecs; dynamically built image type strings containing errors.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

• byte array for resource
• Cannot read default EL properties
• Cannot read EL properties
• could not get byte array from resource
• could not get byte array from resource

AI-assisted analysis of flowable/flowable-engine@d6d39ce1c6 (2026-09-11). Data as JSON: /api/errors/cf9a56cbee511fd1. Report an issue: GitHub.

Appendix: source

Thrown at modules/flowable-image-generator/src/main/java/org/flowable/image/impl/DefaultProcessDiagramCanvas.java:270

            LOGGER.warn("Could not load image for process diagram creation: {}", e.getMessage());
        }
    }

    /**
     * Generates an image of what currently is drawn on the canvas.
     * 
     * Throws an {@link FlowableImageException} when {@link #close()} is already called.
     */
    public InputStream generateImage(String imageType) {
        if (closed) {
            throw new FlowableImageException("ProcessDiagramGenerator already closed");
        }

        try (ByteArrayOutputStream out = new ByteArrayOutputStream()) {
            ImageIO.write(processDiagram, imageType, out);
            return new ByteArrayInputStream(out.toByteArray());
        } catch (IOException e) {
            throw new FlowableImageException("Error while generating process image", e);
        }
    }

    /**
     * Generates an image of what currently is drawn on the canvas.
     * 
     * Throws an {@link FlowableImageException} when {@link #close()} is already called.
     */
    public BufferedImage generateBufferedImage(String imageType) {
        if (closed) {
            throw new FlowableImageException("ProcessDiagramGenerator already closed");
        }

        // Try to remove white space
        minX = (minX <= 5) ? 5 : minX;
        minY = (minY <= 5) ? 5 : minY;
        BufferedImage imageToSerialize = processDiagram;
        imageToSerialize = processDiagram.getSubimage(minX - 5, minY - 5, canvasWidth - minX + 5, canvasHeight - minY + 5);

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