OpenAPITools/openapi-generator · error · RuntimeException

can't load template

Error message

can't load template {name}

What it means

Terminal failure of TemplateManager.readTemplate(name): either getTemplateReader(name) returned null (wrapped 'no file found') or the Scanner/read threw, both caught and logged, after which this RuntimeException is thrown. The template name passed the traversal guard and possibly produced a resolvable path, but the actual read failed. The original exception is logged (with stack trace) but not attached as the cause of the rethrow.

Solutions

1. Check the preceding LOGGER.error line — it prints the underlying cause (null reader vs exception) that this message omits.
2. Verify file permissions/readability of the template in the -t directory and inside the generator JAR.
3. Re-download/rebuild the openapi-generator JAR if classpath resources are corrupt.
4. Ensure the template directory is not being modified concurrently during generation.

Example fix

# before: template dir mounted read-only to another user
--template-dir /opt/tpl   # /opt/tpl/model.mustache mode 600 owned by other user
# after
chmod 644 /opt/tpl/model.mustache  # or chown to the running user

// Check readability before generation
Path p = Paths.get(templateDir, name);
if (!Files.isReadable(p)) throw new IOException("template not readable: " + p);

try { contents = manager.readTemplate(name); } catch (RuntimeException e) { log.error("template read failed for {}", name, e); /* surface LOGGER.error output — it holds the root cause */ throw e; }

When it happens

Trigger: Template exists in the template-dir listing but the file is unreadable (permissions), deleted between resolution and read, or the classpath resource lookup returns a URL whose stream cannot be opened; also the intermediate 'no file found' path when no loader yields a reader.

Common situations: Docker images running as non-root with restricted template file permissions; concurrent builds mutating template directories; stale or corrupted generator JARs where resource entries exist but streams fail; NFS/symlink oddities in CI.

Related errors

• Could not generate model
• Could not generate supporting file
• {name}
• Could not generate api file for
• Could not process model

AI-assisted analysis of OpenAPITools/openapi-generator@fcec517be3 (2026-08-22). Data as JSON: /api/errors/7575ee283c35a405. Report an issue: GitHub.

Appendix: source

Thrown at modules/openapi-generator/src/main/java/org/openapitools/codegen/TemplateManager.java:141

     * @return The raw template contents
     */
    @SuppressWarnings("java:S112")
    // ignored rule java:S112 as RuntimeException is used to match previous exception type
    public String readTemplate(String name) {
        if (name == null || name.contains("..")) {
            throw new IllegalArgumentException("Template location must be constrained to template directory.");
        }
        try (Reader reader = getTemplateReader(name)) {
            if (reader == null) {
                throw new RuntimeException("no file found");
            }
            try (Scanner s = new Scanner(reader).useDelimiter("\\A")) {
                return s.hasNext() ? s.next() : "";
            }
        } catch (Exception e) {
            LOGGER.error("{}", e.getMessage(), e);
        }
        throw new RuntimeException("can't load template " + name);
    }

    @SuppressWarnings({"squid:S2095", "java:S112"})
    // ignored rule squid:S2095 as used in the CLI and it's required to return a reader
    // ignored rule java:S112 as RuntimeException is used to match previous exception type
    public Reader getTemplateReader(String name) {
        try {
            InputStream is = getInputStream(name);
            return new InputStreamReader(is, StandardCharsets.UTF_8);
        } catch (IOException e) {
            LOGGER.error(e.getMessage());
            throw new RuntimeException("can't load template " + name);
        }
    }

    private InputStream getInputStream(String name) throws IOException {
        if (name == null || name.contains("..")) {
            throw new IllegalArgumentException("Template location must be constrained to template directory.");

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