# Background Tasks - `BackgroundTasks`

You can declare a parameter in a *path operation function* or dependency function with the type `BackgroundTasks`, and then you can use it to schedule the execution of background tasks after the response is sent.

You can import it directly from `fastapi`:

```python
from fastapi import BackgroundTasks
```

import javax.inject.Named;
import javax.inject.Singleton;
import javax.xml.stream.XMLStreamException;

import java.io.IOException;
import java.io.UncheckedIOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

# SMTP server settings for main: host:port
mail.smtp.server.main.host.and.port = localhost:25

# The prefix of subject to show test environment or not
mail.subject.test.prefix = [Test]

# The common return path of all mail
mail.return.path = root@localhost


# ========================================================================================
#                                                                                      DB

         */
        public int max_uses;
        /**
         * The current number of connections.
         */
        public int current_uses;
        /**
         * The local path of the share.
         */
        public String path;
        /**
         * The share password (if any).
         */
        public String password;
        /**
         * The size of the security descriptor.
         */

Entonces podemos usar la dependencia con:

{* ../../docs_src/dependencies/tutorial005_an_py310.py hl[23] *}

/// info | Información

Fíjate que solo estamos declarando una dependencia en la *path operation function*, `query_or_cookie_extractor`.

Pero **FastAPI** sabrá que tiene que resolver `query_extractor` primero, para pasar los resultados de eso a `query_or_cookie_extractor` al llamarlo.

///

```mermaid

            if (isDeployedBranch()) {
              withEnv(["JAVA_HOME=${tool "jdk_17_latest"}",
                       "PATH+MAVEN=${ tool "jdk_17_latest" }/bin:${tool "maven_3_latest"}/bin",
                       "MAVEN_OPTS=-Xms4G -Xmx4G -Djava.awt.headless=true"]) {
                sh "mvn clean deploy -DdeployAtEnd=true -B"
              }

            }

            // path to pom.xml
            File currentPom = project.getFile();
            if (currentPom != null) {
                MavenSession session = event.getSession();
                Path current = currentPom.toPath().toAbsolutePath().normalize();
                Path topDirectory = session.getTopDirectory();

* Todo **manejado automáticamente** por el framework.
* Todas las dependencias pueden requerir datos de los requests y **aumentar las restricciones de la path operation** y la documentación automática.
* **Validación automática** incluso para los parámetros de *path operation* definidos en las dependencias.
* Soporte para sistemas de autenticación de usuario complejos, **conexiones a bases de datos**, etc.

    response = client.get("/openapi.json")
    assert response.status_code == 200, response.text
    assert response.json() == {
        "openapi": "3.1.0",
        "info": {"title": "FastAPI", "version": "0.1.0"},
        "paths": {
            "/items/": {
                "get": {
                    "responses": {
                        "200": {
                            "description": "Successful Response",

    response = client.get("openapi.json")
    assert response.json() == snapshot(
        {
            "openapi": "3.1.0",
            "info": {"title": "FastAPI", "version": "0.1.0"},
            "paths": {
                "/": {
                    "get": {
                        "summary": "Test",
                        "operationId": "test__get",
                        "responses": {