OpenAPITools/openapi-generator · error · RuntimeException

Failed to create the folder " + parent.getAbsolutePath() + "

Error message

Failed to create the folder " + parent.getAbsolutePath() + " to store the checksum of the input spec.

What it means

After generation succeeds, CodeGenMojo stores a SHA-256 checksum of the input spec for incremental builds; this RuntimeException (not MojoExecutionException) means File.mkdirs() returned false while creating the parent directory of that checksum file (typically under output/src/main/java/... or the configured output plus .openapi-generator). mkdirs returns false both when creation fails (permissions, read-only mount) and when the path exists as a file or another thread created it concurrently — the code does not distinguish, and the raw RuntimeException then surfaces as 'unexpected error in Open-API generation'.

Source

Thrown at modules/openapi-generator-maven-plugin/src/main/java/org/openapitools/codegen/plugin/CodeGenMojo.java:1130

                            + langCliOption.getOptionHelp().replaceAll("\n", "\n\t    "));
                    System.out.println();
                }
                return;
            }
            adjustAdditionalProperties(config);
            GlobalSettings.log();
            new DefaultGenerator(dryRun).opts(input).generate();

            if (buildContext != null) {
                buildContext.refresh(new File(getCompileSourceRoot()));
            }

            // Store a checksum of the input spec
            File storedInputSpecHashFile = getHashFile(inputSpecFile);
            if (storedInputSpecHashFile.getParent() != null && !new File(storedInputSpecHashFile.getParent()).exists()) {
                File parent = new File(storedInputSpecHashFile.getParent());
                if (!parent.mkdirs()) {
                    throw new RuntimeException("Failed to create the folder " + parent.getAbsolutePath() +
                            " to store the checksum of the input spec.");
                }
            }

            Files.asCharSink(storedInputSpecHashFile, StandardCharsets.UTF_8).write(calculateInputSpecHash(inputSpec));
        } catch (Exception e) {
            // Maven logs exceptions thrown by plugins only if invoked with -e
            // I find it annoying to jump through hoops to get basic diagnostic information,
            // so let's log it in any case:
            if (buildContext != null) {
                buildContext.addMessage(inputSpecFile, 0, 0, "unexpected error in Open-API generation", BuildContext.SEVERITY_WARNING, e);
            }
            getLog().error(e);
            throw new MojoExecutionException(
                    "Code generation failed. See above for the full exception.");
        }
    }

View on GitHub (pinned to fcec517be3)

Solutions

1. Check the parent path printed in the message: if a file occupies it, delete/rename the file and rerun.
2. Ensure the build user has write permission on the whole output directory tree (chmod/chown, or fix the volume mount in Docker).
3. Give each parallel execution its own <output> directory, or disable module-level parallelism for modules running this plugin.
4. Run mvn clean to remove a stale directory structure before regenerating.

# fail fast if the plugin output tree is not writable
OUT=$(mvn -q help:evaluate -Dexpression=openapi.output -DforceStdout 2>/dev/null || echo target/generated-sources)
mkdir -p "$OUT" 2>/dev/null || { echo "cannot create $OUT"; exit 1; }
[ -w "$OUT" ] || { echo "$OUT is not writable"; exit 1; }

When it happens

Trigger: output directory on a read-only filesystem or one the build user cannot write; a file already exists where the directory should be (e.g. a stray file named like the folder); parallel Maven builds (mvn -T) racing two executions into the same output dir; container/CI environments with non-writable mounted volumes.

Common situations: Dockerized builds with a read-only or root-owned volume; CI caching that restored a file where the checksum directory belongs; highly parallel builds sharing one generated-sources directory; NFS/network mounts with flaky mkdir semantics.

Related errors

• Failed to generate .openapi-generator-ignore when the option
• Could not generate supporting file '{ignoreFileNameTarget}'
• Could not generate supporting file '{versionMetadata}'
• Target files must be generated within the output directory;
• Both %s and %s properties were set with different value.

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/c64edd65ebbd885c. Report an issue: GitHub.