assertEquals(2, resources.size(), "Should have two resources now");

        // Find the resource with the custom directory
        Resource customResource = resources.stream()
                .filter(r -> r.getDirectory().endsWith("custom"))
                .findFirst()
                .orElseThrow(() -> new AssertionError("Custom resource not found"));

        // Verify targetPath was preserved through conversion chain

///

## Custom Headers { #custom-headers }

Keep in mind that custom proprietary headers can be added <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers" class="external-link" target="_blank">using the `X-` prefix</a>.

### Custom Generate Unique ID Function { #custom-generate-unique-id-function }

FastAPI uses a **unique ID** for each *path operation*, which is used for the **operation ID** and also for the names of any needed custom models, for requests or responses.

You can customize that function. It takes an `APIRoute` and outputs a string.

## Install custom exception handlers { #install-custom-exception-handlers }

You can add custom exception handlers with <a href="https://www.starlette.dev/exceptions/" class="external-link" target="_blank">the same exception utilities from Starlette</a>.

Let's say you have a custom exception `UnicornException` that you (or a library you use) might `raise`.

And you want to handle this exception globally with FastAPI.

                .put("analysis.analyzer.test_reading_term_analyzer.tokenizer", "standard")
                .put("analysis.analyzer.test_reading_analyzer_ja.type", "custom")
                .put("analysis.analyzer.test_reading_analyzer_ja.tokenizer", "keyword")
                .put("analysis.analyzer.test_reading_term_analyzer_ja.type", "custom")

 + .custom-select,\n.input-group > .form-control-plaintext + .custom-file,\n.input-group > .custom-select + .form-control,\n.input-group > .custom-select + .custom-select,\n.input-group > .custom-select + .custom-file,\n.input-group > .custom-file + .form-control,\n.input-group > .custom-file + .custom-select,\n.input-group > .custom-file + .custom-file {\n  margin-left: -1px;\n}\n\n.input-group > .form-control:focus,\n.input-group > .custom-select:focus,\n.input-group > .custom-file .custom-file-input:focus...

///

## Returning a custom `Response` { #returning-a-custom-response }

The example above shows all the parts you need, but it's not very useful yet, as you could have just returned the `item` directly, and **FastAPI** would put it in a `JSONResponse` for you, converting it to a `dict`, etc. All that by default.

Now, let's see how you could use that to return a custom response.

        }
    }

    /**
     * Functional interface for building XContent with custom logic.
     * Allows clients to provide custom content building implementations.
     */
    public interface XContentBuilderCallback {
        /**
         * Applies custom logic to build XContent using the provided builder and parameters.
         *

        }
    }

    @Nested
    @DisplayName("getMimeType with custom default")
    class GetMimeTypeWithDefault {

        @Test
        @DisplayName("Should return custom default for unknown extensions")
        void testCustomDefaultForUnknown() throws IOException {
            String customDefault = "application/custom";
            assertEquals(customDefault, mimeMap.getMimeType("unknownext", customDefault));

    - topic_repos: ../en/data/topic_repos.yml
  redirects:
    redirect_maps:
      deployment/deta.md: deployment/cloud.md
      advanced/graphql.md: how-to/graphql.md
      advanced/custom-request-and-route.md: how-to/custom-request-and-route.md
      advanced/conditional-openapi.md: how-to/conditional-openapi.md
      advanced/extending-openapi.md: how-to/extending-openapi.md