synchronized (PROTOCOL_HANDLERS) {
            URLStreamHandler handler = (URLStreamHandler) PROTOCOL_HANDLERS.get(protocol);
            if (handler != null) {
                return handler;
            }
            if (factory != null) {
                handler = factory.createURLStreamHandler(protocol);
            }
            if (handler == null) {

In this case, the `startup` event handler function will initialize the items "database" (just a `dict`) with some values.

You can add more than one event handler function.

And your application won't start receiving requests until all the `startup` event handlers have completed.

### `shutdown` event { #shutdown-event }

package jcifs.smb1.https;

/**
 * A <code>URLStreamHandler</code> used to provide NTLM authentication
 * capabilities to the default HTTPS handler.  This acts as a wrapper,
 * handling authentication and passing control to the underlying
 * stream handler.
 */
public class Handler extends jcifs.smb1.http.Handler {

    /**
     * The default HTTPS port (<code>443</code>).
     */
    public static final int DEFAULT_HTTPS_PORT = 443;

import jcifs.context.SingletonContext;

/**
 * URL handler for transparent smb:// URL handling
 *
 */
public class Handler extends URLStreamHandler {

    private static final Logger log = LoggerFactory.getLogger(Handler.class);
    private CIFSContext transportContext;

    /**
     * Default constructor for SMB URL handler.
     */
    public Handler() {
    }

    /**

import java.net.URL;
import java.net.URLConnection;
import java.net.URLStreamHandler;

/**
 * URL handler for SMB1 protocol URLs.
 */
public class Handler extends URLStreamHandler {

    static final URLStreamHandler SMB_HANDLER = new Handler();

    /**
     * Default constructor for SMB1 URL handler.
     */
    public Handler() {
    }

    @Override
    protected int getDefaultPort() {

	_, ok := supportedS3AuthTypes[aType]
	return ok
}

// setAuthMiddleware to validate authorization header for the incoming request.
func setAuthMiddleware(h http.Handler) http.Handler {
	// handler for validating incoming authorization headers.
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		tc, ok := r.Context().Value(mcontext.ContextTraceKey).(*mcontext.TraceCtxt)

 */
package org.codelibs.fess.test.net.protocol.xxx3;

import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLStreamHandler;

public class Handler extends URLStreamHandler {

    public static final String PROTOCOL_TYPE = "test";

    @Override
    protected URLConnection openConnection(URL u) throws IOException {
        return null;
    }

 */
package org.codelibs.fess.test.net.protocol.xxx4;

import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLStreamHandler;

public class Handler extends URLStreamHandler {

    @Override
    protected URLConnection openConnection(URL u) throws IOException {
        return null;
    }

 */
package org.codelibs.fess.test.net.protocol.xxx2;

import java.io.IOException;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLStreamHandler;

public class Handler extends URLStreamHandler {

    public static final String PROTOCOL_TYPE = "file";

    @Override
    protected URLConnection openConnection(URL u) throws IOException {
        return null;
    }

///

## Override the default exception handlers { #override-the-default-exception-handlers }

**FastAPI** has some default exception handlers.

These handlers are in charge of returning the default JSON responses when you `raise` an `HTTPException` and when the request has invalid data.

You can override these exception handlers with your own.