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The core jetty server artifact.
There is a newer version: 12.1.0.alpha0
//
// ========================================================================
// Copyright (c) 1995 Mort Bay Consulting Pty Ltd and others.
//
// This program and the accompanying materials are made available under the
// terms of the Eclipse Public License v. 2.0 which is available at
// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
// which is available at https://www.apache.org/licenses/LICENSE-2.0.
//
// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
// ========================================================================
//

package org.eclipse.jetty.server.handler;

import java.io.IOException;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.eclipse.jetty.http.HttpURI;
import org.eclipse.jetty.server.Handler;
import org.eclipse.jetty.server.Request;
import org.eclipse.jetty.server.Response;
import org.eclipse.jetty.util.Callback;
import org.eclipse.jetty.util.ExceptionUtil;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * An {@link ErrorHandler} that can re-handle a request at an error page location.
 */
public abstract class ReHandlingErrorHandler extends ErrorHandler
{
    private static final Logger LOG = LoggerFactory.getLogger(ReHandlingErrorHandler.class);

    private final Handler _handler;

    protected ReHandlingErrorHandler(Handler handler)
    {
        _handler = handler;
    }

    @Override
    public InvocationType getInvocationType()
    {
        return _handler.getInvocationType();
    }

    @Override
    protected void generateResponse(Request request, Response response, int code, String message, Throwable cause, Callback callback) throws IOException
    {
        if (request.getAttribute(ReHandlingErrorHandler.class.getName()) == null)
        {
            String pathInContext = getReHandlePathInContext(request, code, cause);

            if (pathInContext != null)
            {
                request.setAttribute(ReHandlingErrorHandler.class.getName(), pathInContext);
                HttpURI uri = Request.newHttpURIFrom(request, pathInContext);
                Request reRequest = Request.serveAs(request, uri);

                try
                {
                    response.setStatus(200);
                    if (_handler.handle(reRequest, response, callback))
                        return;
                }
                catch (Exception e)
                {
                    if (LOG.isDebugEnabled())
                        LOG.debug("Unable to process error {}", reRequest, e);
                    ExceptionUtil.addSuppressedIfNotAssociated(cause, e);
                    response.setStatus(code);
                }
            }
        }
        super.generateResponse(request, response, code, message, cause, callback);
    }

    protected abstract String getReHandlePathInContext(Request request, int code, Throwable cause);

    /**
     * An {@link ReHandlingErrorHandler} that uses a map of error codes to select a page.
     */
    public static class ByHttpStatus extends ReHandlingErrorHandler
    {
        private final Map _statusMap = new ConcurrentHashMap<>();

        public ByHttpStatus(Handler handler)
        {
            super(handler);
        }

        @Override
        protected String getReHandlePathInContext(Request request, int code, Throwable cause)
        {
            return get(code);
        }

        public String put(int code, String pathInContext)
        {
            return _statusMap.put(code, pathInContext);
        }

        public String get(int code)
        {
            return _statusMap.get(code);
        }

        public String remove(int code)
        {
            return _statusMap.remove(code);
        }
    }
}