com.pushtechnology.diffusion.examples.TimeSeriesQueryExample Maven / Gradle / Ivy
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* Copyright (C) 2016, 2023 DiffusionData Ltd.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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* See the License for the specific language governing permissions and
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*******************************************************************************/
package com.pushtechnology.diffusion.examples;
import static java.lang.Math.max;
import static java.util.Collections.unmodifiableSortedMap;
import java.io.IOException;
import java.time.Instant;
import java.util.SortedMap;
import java.util.TreeMap;
import java.util.function.Consumer;
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.dataformat.cbor.CBORFactory;
import com.pushtechnology.diffusion.client.callbacks.ErrorReason;
import com.pushtechnology.diffusion.client.features.TimeSeries;
import com.pushtechnology.diffusion.client.features.TimeSeries.Event;
import com.pushtechnology.diffusion.client.features.TimeSeries.Query;
import com.pushtechnology.diffusion.client.features.Topics;
import com.pushtechnology.diffusion.client.features.Topics.ValueStream;
import com.pushtechnology.diffusion.client.session.Session;
import com.pushtechnology.diffusion.client.topics.details.TopicSpecification;
import com.pushtechnology.diffusion.datatype.json.JSON;
/**
* Demonstrate the TimeSeries API.
*
*
* This demonstrates client-side view maintenance for a simple chat application.
*
*
* The view is modeled by the {@link ChatView} class. This has a start time, and
* a map of sequence number to messages that have occurred after the start time.
*
*
* The {@link #subscribeChatView subscribeChatView} method subscribes a session
* to a time series topic of chat messages stored as JSON objects. ChatView
* models each chat message using the {@link ChatMessage} class. Once
* subscribed, the ChatView will be asynchronously updated with new messages and
* edits to existing messages.
*
* @author DiffusionData Limited
* @since 6.0
*/
public final class TimeSeriesQueryExample {
/** Jackson ObjectMapper used by {@link #jsonToChat(JSON)}. */
private static final ObjectMapper CBOR_MAPPER =
new ObjectMapper(new CBORFactory());
private TimeSeriesQueryExample() {
}
/**
* Connect a ChatView to a time series topic.
*
* @param chatView the ChatView
* @param chatTopicPath path of a JSON time series topic storing chat
* messages
* @param errorHandler called if an operation fails
*/
public static void subscribeChatView(
Session session,
ChatView chatView,
String chatTopicPath,
Consumer errorHandler) {
final Topics topics = session.feature(Topics.class);
final ValueStream> subscriptionStream =
new ValueStream.Default>() {
private volatile boolean initialValue = true;
@Override
public void onValue(
String topicPath,
TopicSpecification specification,
Event oldEvent,
Event event) {
// When the subscription initially completes, the stream
// will receive an initial range of events from the server.
// If there is a gap between the latest event processed by
// the ChatView and the first event received, query the
// time series topic to retrieve the missing events.
if (initialValue &&
event.sequence() > chatView.expectedNextSequence()) {
initialValue = false;
final Query query = chatView.missingEventQuery(
session.feature(TimeSeries.class),
event.sequence());
query
.selectFrom(chatTopicPath)
.whenComplete((result, e) -> {
if (e != null) {
topics.removeStream(this);
errorHandler.accept(e);
}
else {
result.stream().forEach(chatView::addEvent);
}
});
}
chatView.addEvent(event);
}
@Override
public void onError(ErrorReason errorReason) {
errorHandler.accept(new RuntimeException(
"Subscription stream failed: " + errorReason));
}
};
topics.addTimeSeriesStream(chatTopicPath, JSON.class, subscriptionStream);
topics.subscribe(chatTopicPath)
.whenComplete((result, e) -> {
if (e != null) {
topics.removeStream(subscriptionStream);
errorHandler.accept(e);
}
});
}
/**
* A client-side model of a time series of ChatMessages.
*/
public static class ChatView {
private final Instant startOfView;
private final SortedMap> messages =
new TreeMap<>();
private long latestSequence = -1;
/**
* Constructor.
*
* @param startOfView the start of the view
*/
public ChatView(Instant startOfView) {
this.startOfView = startOfView;
}
/**
* @return an ordered map of sequence number -> chat message events
*/
public SortedMap> getMessages() {
return unmodifiableSortedMap(messages);
}
private synchronized void addEvent(Event event) {
if (event.timestamp() >= startOfView.toEpochMilli()) {
messages.put(
event.originalEvent().sequence(),
event.withValue(jsonToChat(event.value())));
}
latestSequence = max(latestSequence, event.sequence());
}
private synchronized long expectedNextSequence() {
return latestSequence + 1;
}
/**
* @return a query configured to return all events that affect the view
* from the next expected event until receivedSequence
*/
private synchronized Query missingEventQuery(
TimeSeries timeSeries,
long receivedSequence) {
return timeSeries.rangeQuery()
.from(startOfView)
.editRange().from(latestSequence + 1)
.to(receivedSequence - 1)
.as(JSON.class);
}
}
/**
* Simple model of a chat message that combines application metadata
* (priority, senderId) with a textual message.
*/
public static class ChatMessage {
private final String text;
private final int priority;
private final int senderId;
/**
* Constructor.
*/
@JsonCreator
public ChatMessage(
@JsonProperty("text") String text,
@JsonProperty("priority") int priority,
@JsonProperty("senderId") int senderId) {
this.text = text;
this.priority = priority;
this.senderId = senderId;
}
/**
* @return the message text.
*/
public String getText() {
return text;
}
/**
* @return a priority code; high priority messages may be rendered
* differently
*/
public int getPriority() {
return priority;
}
/**
* Used by the send to de-duplicate pending messages on reconnection.
*/
public int getSenderId() {
return senderId;
}
}
/**
* Use the third-party Jackson library to parse a JSON message as a
* ChatMessage.
*/
private static ChatMessage jsonToChat(JSON value) {
try {
return CBOR_MAPPER.readValue(value.asInputStream(), ChatMessage.class);
}
catch (IOException e) {
throw new RuntimeException("Failed to parse event as chat message", e);
}
}
}