platform/northbound/http-tools/src/main/java/org/eclipse/sensinact/gateway/nthbnd/http/callback/internal/CallbackServlet.java

/*
 * Copyright (c) 2017 CEA.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    CEA - initial API and implementation
 */
package org.eclipse.sensinact.gateway.nthbnd.http.callback.internal;

import org.eclipse.sensinact.gateway.common.bundle.Mediator;
import org.eclipse.sensinact.gateway.nthbnd.http.callback.CallbackContext;
import org.eclipse.sensinact.gateway.nthbnd.http.callback.CallbackService;

import javax.servlet.AsyncContext;
import javax.servlet.Servlet;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.WriteListener;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
 * Callback servlet
 *
 * @author <a href="mailto:christophe.munilla@cea.fr">Christophe Munilla</a>
 */
@SuppressWarnings("serial")
@WebServlet(asyncSupported = true)
public class CallbackServlet extends HttpServlet implements Servlet{
		
    public static enum CALLBACK_METHOD {
        GET, POST, PUT, DELETE;
    }

    private Mediator mediator;

	private CallbackService callbackService;

    /**
     * Constructor
     *
     * @param mediator the {@link Mediator} allowing the CallbackServlet
     * to be instantiated to interact with the OSGi host environment
     * @param callbackService the {@link CallbackService} allowing the
     * CallbackServlet to be instantiated to process the callback request
     */
    public CallbackServlet(Mediator mediator, CallbackService callbackService) {
        this.mediator = mediator;
        this.callbackService = callbackService;
    }
    
    public void init(ServletConfig config) throws ServletException {
    	try {
    		super.init(config);
    	}catch(Exception e) {
    		e.printStackTrace();
    		throw new ServletException(e);
    	} 
    }

    private final void doCall(final CALLBACK_METHOD method, HttpServletRequest request, HttpServletResponse response) throws IOException {
    	if (response.isCommitted()) {       	
    		return;
        }
        final AsyncContext asyncContext;
        if (request.isAsyncStarted()) {
            asyncContext = request.getAsyncContext();

        } else {
            asyncContext = request.startAsync(request, response);
        }
        final CallbackContext context = new CallbackContext(mediator, method.name(), asyncContext);

        response.getOutputStream().setWriteListener(new WriteListener() {
            @Override
            public void onWritePossible() throws IOException {
                HttpServletRequest request = (HttpServletRequest) asyncContext.getRequest();
                HttpServletResponse response = (HttpServletResponse) asyncContext.getResponse();
                try {
                    if (CallbackServlet.this.callbackService != null) {
                    	CallbackServlet.this.callbackService.process(context);
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                    onError(e);
                    response.sendError(520, "Internal server error");

                } catch (Error e) {
                    e.printStackTrace();

                } finally {
                    if (request.isAsyncStarted()) {
                        asyncContext.complete();
                    }
                }
            }

            @Override
            public void onError(Throwable t) {
                mediator.error(t);
            }
        });
    }

    /**
     * @inheritDoc
     * @see javax.servlet.http.HttpServlet#
     * doGet(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
     */
    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        doCall(CALLBACK_METHOD.GET, request, response);
    }

    /**
     * @inheritDoc
     * @see javax.servlet.http.HttpServlet#
     * doPost(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
     */
    @Override
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
        doCall(CALLBACK_METHOD.POST, request, response);
    }

    /**
     * @inheritDoc
     * @see javax.servlet.http.HttpServlet#
     * doPut(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
     */
    @Override
    public void doPut(HttpServletRequest request, HttpServletResponse response) throws IOException {
        doCall(CALLBACK_METHOD.PUT, request, response);
    }

    /**
     * @inheritDoc
     * @see javax.servlet.http.HttpServlet#
     * doDelete(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
     */
    @Override
    public void doDelete(HttpServletRequest request, HttpServletResponse response) throws IOException {
        doCall(CALLBACK_METHOD.DELETE, request, response);
    }
}