# Lifespan Events

You can define logic (code) that should be executed before the application **starts up**. This means that this code will be executed **once**, **before** the application **starts receiving requests**.

The same way, you can define logic (code) that should be executed when the application is **shutting down**. In this case, this code will be executed **once**, **after** having handled possibly **many requests**.

# Custom Request and APIRoute class

In some cases, you may want to override the logic used by the `Request` and `APIRoute` classes.

In particular, this may be a good alternative to logic in a middleware.

For example, if you want to read or manipulate the request body before it is processed by your application.

/// danger

This is an "advanced" feature.

If you are just starting with **FastAPI** you might want to skip this section.

///

                + replacement.getVersionRange() + " to: " + newRange + " )");
    }

    /**
     * The logic used here used to be a copy of the logic used in the DefaultArtifactCollector, and this method was
     * called right before the actual version/artifactScope changes were done. However, a different set of conditionals

  // it will be compatible with it: the name will be updated by device placement
  // logic to refer to the specific device chosen.
  //
  // Example: If one calls `op->SetDeviceName("/device:GPU")`, the value
  // returned by DeviceName should be "/device:GPU:*" until a particular GPU is
  // chosen for the operation by the device placement logic in the
  // executor. After that, the value returned by DeviceName will be a full

 This is the model for Maven toolchain in <<<org.apache.maven.toolchain>>> package,
 delegating content to {{{../api/maven-api-toolchain/index.html}Maven 4 API immutable toolchain}}. All the effective model
 building logic from multiple toolchains files is done in {{{../maven-toolchain-builder/}Maven Toolchain Builder}}.

 The following are generated from this model:

 This is strictly the model for Maven POM (Project Object Model) in <<<org.apache.maven.model>>> package,
 delegating content to {{{../api/maven-api-model/index.html}Maven 4 API immutable model}}. All the effective model
 building logic from multiple POMs and building context is done in {{{../maven-model-builder/}Maven Model Builder}}.

 The following are generated from this model:

import org.codehaus.plexus.interpolation.RegexBasedInterpolator;

/**
 * Use a regular expression search to find and resolve expressions within the POM.
 *
 * TODO Consolidate this logic with the PluginParameterExpressionEvaluator, minus deprecations/bans.
 */
@Deprecated
public class RegexBasedModelInterpolator extends AbstractStringBasedModelInterpolator {

Maven Settings Model

 This is the model for Maven settings in <<<org.apache.maven.settings>>> package,
 delegating content to {{{../api/maven-api-settings/index.html}Maven 4 API immutable settings}}. All the effective model
 building logic from multiple settings files is done in {{{../maven-settings-builder/}Maven Settings Builder}}.

 The following are generated from this model:

And **your users** define in some way (for example in a web dashboard somewhere) the **URL** where your app should send those requests.

All the **logic** about how to register the URLs for webhooks and the code to actually send those requests is up to you. You write it however you want to in **your own code**.

## Documenting webhooks with **FastAPI** and OpenAPI

This is very useful when you need to:

* Have shared logic (the same code logic again and again).
* Share database connections.
* Enforce security, authentication, role requirements, etc.
* And many other things...

All these, while minimizing code repetition.

## First Steps