# Save it for use later to prevent xsrf attacks

    state = str(uuid4())
    params = {"client_id": client_id,
              "response_type": "code",
              "state": state,
              "redirect_uri": callback_uri,
              "scope": "openid"}

    url = authorize_url + "?" + urllib.parse.urlencode(params)
    return url


@app.route('/oauth2/callback')
def callback():

| Params     | Value    |
| :--        | :--      |
| *Type*     | *String* |
| *Required* | *No*     |

### RoleArn

The role ARN to use. This must be specified if and only if the web identity provider is configured with a role policy.

| Params     | Value    |
| :--        | :--      |
| *Type*     | *String* |

          </models>
          <params>
            <param>forcedIOModelVersion=1.1.0</param>
            <param>packageModelV3=org.apache.maven.artifact.repository.metadata</param>
            <param>packageModelV4=org.apache.maven.api.metadata</param>
            <param>packageToolV4=org.apache.maven.artifact.repository.metadata.io</param>
          </params>

        try {
            final SearchRenderData data = new SearchRenderData();
            final JsonRequestParams params = new JsonRequestParams(request, fessConfig);
            query = params.getQuery();
            searchHelper.search(params, data, OptionalThing.empty());
            final String execTime = data.getExecTime();
            final String queryTime = Long.toString(data.getQueryTime());

              </models>
              <templates>
                <template>model.vm</template>
              </templates>
              <params>
                <param>packageModelV4=org.apache.maven.api.metadata</param>
              </params>
            </configuration>
          </execution>
          <execution>
            <id>plugin-doc</id>
            <goals>
              <goal>xdoc</goal>

            <template>reader-stax.vm</template>
            <template>writer-stax.vm</template>
          </templates>
          <params>
            <param>packageModelV4=org.apache.maven.api.cli.extensions</param>
            <param>packageToolV4=org.apache.maven.cli.internal.extension.io</param>
          </params>
          <velocityBasedir>${project.basedir}/../../src/mdo</velocityBasedir>
        </configuration>
        <executions>

        Object proxy, Method method, @Nullable Object[] args) {
      Invokable<?, ?> invokable = interfaceType.method(method);
      ImmutableList<Parameter> params = invokable.getParameters();
      for (int i = 0; i < args.length; i++) {
        Parameter param = params.get(i);
        if (!isNullable(param)) {
          checkNotNull(args[i]);
        }
      }

///

```Python hl_lines="11-14"
{!> ../../docs_src/body_fields/tutorial001.py!}
```

////

`Field` 的工作方式和 `Query`、`Path`、`Body` 相同，参数也相同。

/// note | "技术细节"

实际上，`Query`、`Path` 都是 `Params` 的子类，而 `Params` 类又是 Pydantic 中 `FieldInfo` 的子类。

Pydantic 的 `Field` 返回也是 `FieldInfo` 的类实例。

`Body` 直接返回的也是 `FieldInfo` 的子类的对象。后文还会介绍一些 `Body` 的子类。

注意，从 `fastapi` 导入的 `Query`、`Path` 等对象实际上都是返回特殊类的函数。

///

            }
            saveInfo(messages -> messages.addSuccessUploadStemmeroverrideFile(GLOBAL));
            return redirectWith(getClass(), moreUrl("list/1").params("dictId", form.dictId));
        }).orElseGet(() -> {
            throwValidationError(messages -> messages.addErrorsFailedToUploadStemmeroverrideFile(GLOBAL), () -> uploadpage(form.dictId));
            return null;

            }
            saveInfo(messages -> messages.addSuccessUploadMappingFile(GLOBAL));
            return redirectWith(getClass(), moreUrl("list/1").params("dictId", form.dictId));
        }).orElseGet(() -> {
            throwValidationError(messages -> messages.addErrorsFailedToUploadMappingFile(GLOBAL), () -> uploadpage(form.dictId));
            return null;
        });