# Header Parameter Models { #header-parameter-models }

If you have a group of related **header parameters**, you can create a **Pydantic model** to declare them.

This would allow you to **re-use the model** in **multiple places** and also to declare validations and metadata for all the parameters at once. 😎

/// note

This is supported since FastAPI version `0.115.0`. 🤓

///

    }
  }

  /*
   * Preconditions.checkNotNull is *intended* for performing eager null checks on parameters that a
   * nullness checker can already "prove" are non-null. That means that the first parameter to
   * checkNotNull *should* be annotated to require it to be non-null.
   *
   * However, for a variety of reasons, Google developers have written a ton of code over the past

# Query Parameters and String Validations { #query-parameters-and-string-validations }

**FastAPI** allows you to declare additional information and validation for your parameters.

Let's take this application as example:

{* ../../docs_src/query_params_str_validations/tutorial001_py310.py hl[7] *}

    }

    public void test_convertParameterMap() {
        String parameters;
        Map<String, String> parameterMap;

        parameters = "";
        parameterMap = ParameterUtil.parse(parameters);
        assertEquals(0, parameterMap.size());

        parameters = "domain";
        parameterMap = ParameterUtil.parse(parameters);
        assertEquals(1, parameterMap.size());

            throw new IORuntimeException(e);
        }
    }

    /**
     * Parses request parameters from a string.
     * @param params The parameter string.
     * @param paramList Additional parameters.
     * @param encoding The encoding.
     * @return The HttpEntity containing the parsed parameters.
     */

///

/// tip

To declare File bodies, you need to use `File`, because otherwise the parameters would be interpreted as query parameters or body (JSON) parameters.

///

The files will be uploaded as "form data".

If you declare the type of your *path operation function* parameter as `bytes`, **FastAPI** will read the file for you and you will receive the contents as `bytes`.

    }

    /**
     * Stores a parameter value with the specified key.
     *
     * @param key the parameter key, must not be null
     * @param value the parameter value, may be null
     */
    public void put(final String key, final Object value) {
        params.put(key, value);
    }

    /**
     * Retrieves a parameter value by key.
     *
     * @param key the parameter key to look up

   * parameters.
   */
  public MediaType withoutParameters() {
    return parameters.isEmpty() ? this : create(type, subtype);
  }

  /**
   * Replaces all parameters with the given parameters.
   *
   * @throws IllegalArgumentException if any parameter or value is invalid
   */

# Cookie Parameters { #cookie-parameters }

You can define Cookie parameters the same way you define `Query` and `Path` parameters.

## Import `Cookie` { #import-cookie }

First import `Cookie`:

{* ../../docs_src/cookie_params/tutorial001_an_py310.py hl[3] *}

## Declare `Cookie` parameters { #declare-cookie-parameters }

Then declare the cookie parameters using the same structure as with `Path` and `Query`.

  fun emptyCache(parameters: Pair<FileSystem, Boolean>) {
    setUp(parameters.first, parameters.second)
    cache.close()
    assertJournalEquals()
  }

  @ParameterizedTest
  @ArgumentsSource(FileSystemParamProvider::class)
  fun recoverFromInitializationFailure(parameters: Pair<FileSystem, Boolean>) {
    setUp(parameters.first, parameters.second)