from typing import Optional

from fastapi import FastAPI, Security
from fastapi.security import OAuth2PasswordBearer
from fastapi.testclient import TestClient

app = FastAPI()

oauth2_scheme = OAuth2PasswordBearer(
    tokenUrl="/token",
    description="OAuth2PasswordBearer security scheme",
    auto_error=False,
)


@app.get("/items/")
async def read_items(token: Optional[str] = Security(oauth2_scheme)):
    if token is None:

 */
package org.apache.maven.api.services;

import java.io.IOException;
import java.lang.module.ModuleDescriptor;
import java.nio.file.Path;
import java.util.List;
import java.util.Map;
import java.util.Optional;

import org.apache.maven.api.Dependency;
import org.apache.maven.api.DependencyScope;
import org.apache.maven.api.JavaPathType;
import org.apache.maven.api.Node;
import org.apache.maven.api.PathType;

 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.maven.api.services;

import java.util.Optional;

import org.apache.maven.api.ExtensibleEnum;
import org.apache.maven.api.Service;
import org.apache.maven.api.annotations.Nonnull;

/**

 * exception when queried.
 */
fun <T: Any> atMostOneOf(vararg providers: Provider<T>): Provider<T> {
    return providers.map { provider ->
        provider.map {
            Optional.of(it)
        }.orElse(
            Optional.empty<T>()
        )
    }.reduce { acc, next ->
        acc.zip(next) { left, right ->
            when {
                left.isPresent -> {

                default:
                    // could not parse expression
                    return null;
            }
        }

        if (value instanceof Optional<?> optional) {
            value = optional.orElse(null);
        }
        return value;
    }

    private static Object getMappedValue(

- **路径**中声明了相同参数的参数，是路径参数
- 类型是（`int`、`float`、`str`、`bool` 等）**单类型**的参数，是**查询**参数
- 类型是 **Pydantic 模型**的参数，是**请求体**

/// note | 笔记

因为默认值是 `None`， FastAPI 会把 `q` 当作可选参数。

FastAPI 不使用 `Optional[str]` 中的 `Optional`， 但 `Optional` 可以让编辑器提供更好的支持，并检测错误。

///

## 不使用 Pydantic

    }

    /**
     * Implementation method for reading an XML node from an input stream.
     *
     * @param input the input stream to read from
     * @param locationBuilder optional builder for creating input location objects
     * @return the parsed XML node
     * @throws XMLStreamException if there is an error parsing the XML
     */

                    }
                }

                @Nonnull
                @Override
                public Optional<org.apache.maven.api.Toolchain> createDefaultToolchain()
                        throws ToolchainFactoryException {
                    return Optional.ofNullable(v3Factory.createDefaultToolchain())
                            .map(ToolchainManagerFactory.this::getToolchainV4);
                }

from typing import Optional

from fastapi import APIRouter, FastAPI
from fastapi.testclient import TestClient
from pydantic import BaseModel, HttpUrl

app = FastAPI()


class Invoice(BaseModel):
    id: str
    title: Optional[str] = None
    customer: str
    total: float


class InvoiceEvent(BaseModel):
    description: str
    paid: bool


class InvoiceEventReceived(BaseModel):
    ok: bool

     *
     * @param project the potentially forked project
     * @return an Optional containing the original project if the input is a forked project,
     *         or an empty Optional if the input is already the original project
     * @throws IllegalArgumentException if the project is null
     */
    @Nonnull
    Optional<Project> getExecutionProject(@Nonnull Project project);