source: PerfectFit/Web/src/main/java/perfectfit/ChatServlet.java

package perfectfit;

import java.io.IOException;
import java.io.InputStream;
import java.util.Map;
import java.util.Map.Entry;
import java.util.stream.Collectors;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.exc.StreamReadException;
import com.fasterxml.jackson.databind.DatabindException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

import tudelft.dialogmanager.DialogPhase;
import tudelft.dialogmanager.DialogState;
import tudelft.dialogmanager.answertypes.InvalidAnswerException;
import tudelft.dialogmanager.parameters.DoubleValue;
import tudelft.dialogmanager.parameters.Parameters;
import tudelft.dialogmanager.stimuli.Stimulus;
import tudelft.dialogmanager.stimuli.Textual;
import tudelft.mentalhealth.perfectfit.updatefuncs.CheckDeadline;
import tudelft.mentalhealth.perfectfit.updatefuncs.DateString;
import tudelft.mentalhealth.perfectfit.updatefuncs.Example;
import tudelft.mentalhealth.perfectfit.updatefuncs.StringLength;
import tudelft.mentalhealth.perfectfit.updatefuncs.Time;
import tudelft.mentalhealth.perfectfit.updatefuncs.TimeDifference;

/**
 * Servlet to handle user actions and reply with bot response.
 */
@SuppressWarnings("serial")
public class ChatServlet extends HttpServlet {
        private final static ObjectMapper jackson = new ObjectMapper();
        static {
                jackson.registerSubtypes(Example.class, Time.class, CheckDeadline.class,
                                TimeDifference.class, StringLength.class, DateString.class);
        }
        InputStream stream = getClass().getClassLoader()
                        .getResourceAsStream("dialog.json");

        /**
         * This service gets the current stimulation serialized as json. replies
         * NOT_ACCEPTABLE if chat was finished already. Replies BAD_REQUEST if the
         * given text answer is not acceptable in current state. Replies OK if text
         * answer was processed succesfully.
         */
        @Override
        protected void doPost(HttpServletRequest request,
                        HttpServletResponse response) throws ServletException, IOException {
                DialogState state = getState(request.getSession());
                if (state.isFinal()) {
                        response.sendError(HttpServletResponse.SC_NOT_ACCEPTABLE,
                                        "Chat is finished. Try starting a new session");
                        return;
                }

                String usertext = request.getReader().lines()
                                .collect(Collectors.joining(System.lineSeparator()));
                try {
                        state = state.with(usertext);
                } catch (InvalidAnswerException e) {
                        e.printStackTrace();
                        response.sendError(HttpServletResponse.SC_BAD_REQUEST,
                                        e.getMessage());

                }
                // run evaluation and then prepare the next state immediately.
                state = state.withUpdate(false);
                if (!state.isFinal()) {
                        state = state.withUpdate(true);
                }
                request.getSession().setAttribute("state", state);

                response.setStatus(HttpServletResponse.SC_OK);
        }

        @Override
        protected void doGet(HttpServletRequest request,
                        HttpServletResponse response) throws ServletException, IOException {
                DialogState state = getState(request.getSession());
                if (state == null) {
                        response.sendError(HttpServletResponse.SC_PRECONDITION_FAILED,
                                        "Please enter the chat through the form");
                        return;
                }
                if (state.isFinal()) {
                        response.sendError(400,
                                        "Chat is finished. Try starting a new session");
                        return;
                }

                DialogPhase phase = state.getCurrentPhase();
                Stimulus stimulus = phase.getStimulation()
                                .substitute(state.getParameters());

                StimAnswer reply = new StimAnswer(stimulus, phase.getAnswer());
                if (!(stimulus instanceof Textual)) {
                        throw new IllegalStateException(
                                        "The Demo App only supports Textual.");
                }

                response.setContentType("text/json;charset=UTF-8");
                response.getWriter().append(jackson.writeValueAsString(reply));
        }

        /**
         * A OPTIONS command resets the state, using the query string in request.
         * This can be used to restart a session, and must be used to load query
         * arguments into the state. CONNECT seems not available , otherwise that
         * would have been better
         */
        @Override
        protected void doOptions(HttpServletRequest request,
                        HttpServletResponse response)
                        throws StreamReadException, DatabindException, IOException {
                System.out.println("Initializing session");
                InputStream stream = getClass().getClassLoader()
                                .getResourceAsStream("dialog.json");

                DialogState state = jackson.readValue(stream, DialogState.class);

                state = addVariables(state, request.getParameterMap());

                // initialize the preparation so that we have the text ready.
                state = state.withUpdate(true);
                request.getSession().setAttribute("state", state);

        }

        /**
         * @param state the current state.
         * @param map   a querystring eg 'age=25&weight=96'
         * @return DialogState with the parameters added.
         * 
         */
        private DialogState addVariables(DialogState state,
                        Map<String, String[]> map) {
                Parameters params = state.getParameters();
                for (Entry<String, String[]> entry : map.entrySet()) {
                        params = params.with(entry.getKey(),
                                        new DoubleValue(Double.valueOf(entry.getValue()[0])));
                }
                return state.with(params);

        }

        /**
         * 
         * @param httpSession the current session
         * @return current {@link DialogState} for this session
         * @throws Exception if error occurs reading the initial state. Should not
         *                   happen
         */
        private DialogState getState(HttpSession httpSession)
                        throws JsonParseException, JsonMappingException, IOException {
                return (DialogState) httpSession.getAttribute("state");
        }
}