<dependency>
    <groupId>org.eclipse.californium</groupId>
    <artifactId>californium-core</artifactId>
    <version>2.0.0-M1</version>
</dependency>

public static void main(String[] args) {

        // 创建服务端
        CoapServer server = new CoapServer();
        // 启动服务端
        server.start();

}

public CoapServer(final NetworkConfig config, final int... ports) {
    
    // 初始化配置	
    if (config != null) {
        this.config = config;
    } else {
        this.config = NetworkConfig.getStandard();
    }

    // 初始化Resource
    this.root = createRoot();

    // 初始化MessageDeliverer
    this.deliverer = new ServerMessageDeliverer(root);

    CoapResource wellKnown = new CoapResource(".well-known");
    wellKnown.setVisible(false);
    wellKnown.add(new DiscoveryResource(root));
    root.add(wellKnown);

    // 初始化EndPoints
    this.endpoints = new ArrayList<>();

    // 初始化线程池
    this.executor = Executors.newScheduledThreadPool(this.config.getInt(NetworkConfig.Keys.PROTOCOL_STAGE_THREAD_COUNT), new NamedThreadFactory("CoapServer#")); 

    // 添加Endpoint
    for (int port : ports) {
        addEndpoint(new CoapEndpoint(port, this.config));
    }
}

public void start() {

    // 如果没有一个Endpoint与CoapServer进行绑定，那就创建一个默认的Endpoint
    ...

    // 一个一个地将Endpoint启动
    int started = 0;
    for (Endpoint ep:endpoints) {
        try {
            ep.start();
            ++started;
        } catch (IOException e) {
            LOGGER.log(Level.SEVERE, "Cannot start server endpoint [" + ep.getAddress() + "]", e);
        }
    }
    if (started==0) {
        throw new IllegalStateException("None of the server endpoints could be started");
    }
}

public static void main(String[] args) throws URISyntaxException {
        
    // 确定请求路径
    URI uri = new URI("127.0.0.1");

    // 创建客户端
    CoapClient client = new CoapClient(uri);
    
    // 发起一个GET请求
    client.get();

}

public CoapEndpoint(Connector connector, NetworkConfig config, ObservationStore store) {
    this.config = config;
    this.connector = connector;
    if (store == null) {
        this.matcher = new Matcher(config, new NotificationDispatcher(), new InMemoryObservationStore());
    } else {
        this.matcher = new Matcher(config, new NotificationDispatcher(), store);
    }
    this.coapstack = new CoapStack(config, new OutboxImpl());
    this.connector.setRawDataReceiver(new InboxImpl());
}

public void receiveData(final RawData raw) {

    // 参数校验
    ...

    // 启动线程处理收到的消息
    runInProtocolStage(new Runnable() {
        @Override
        public void run() {
            receiveMessage(raw);
        }
    });

}

private void receiveMessage(final RawData raw) {
    
    // 解析数据源
    DataParser parser = new DataParser(raw.getBytes());

    // 如果是请求数据
    if (parser.isRequest()) {
        // 一些非关键操作
        ...
        
        // 消息拦截器接收请求
        for (MessageInterceptor interceptor:interceptors) {
            interceptor.receiveRequest(request);
        }
    
        // 匹配器接收请求，并返回Exchange对象
        Exchange exchange = matcher.receiveRequest(request);
        
        // Coap协议栈接收请求
        coapstack.receiveRequest(exchange, request);
    }
    
    // 如果是响应数据，则与请求数据一样，分别由消息拦截器、匹配器、Coap协议栈接收响应
    ...

    // 如果是空数据，则与请求数据、响应数据一样，分别由消息拦截器、匹配器、Coap协议栈接收空数据
    ...
    
    // 一些非关键操作
    ...

}

public Exchange receiveRequest(Request request) {

    // 根据Request请求，填充并返回Exchange对象
    ...

}

public CoapStack(NetworkConfig config, Outbox outbox) {

    // 初始化栈顶
    this.top = new StackTopAdapter();
    
    // 初始化栈底
    this.bottom = new StackBottomAdapter();
    
    // 初始化出口
    this.outbox = outbox;

    // 初始化ReliabilityLayer
    ...

    // 初始化层级
    this.layers = 
        new Layer.TopDownBuilder()
        .add(top)
        .add(new ObserveLayer(config))
        .add(new BlockwiseLayer(config))
        .add(reliabilityLayer)
        .add(bottom)
        .create();

}

public void receiveRequest(Exchange exchange, Request request) {
    bottom.receiveRequest(exchange, request);
}

public void receiveRequest(Exchange exchange, Request request) {

    // 一些非关键操作
    ...
    
    // 将请求传递给消息分发器
    deliverer.deliverRequest(exchange);
    
}

public void deliverRequest(final Exchange exchange) {

    // 从exchange里获取request
    Request request = exchange.getRequest();
    
    // 从request里获取请求路径
    List<String> path = request.getOptions().getUriPath();
    
    // 找出请求路径对应的Resource
    final Resource resource = findResource(path);
    
    // 一些非关键操作
    ...
    
    // 由Resource来真正地处理请求
    resource.handleRequest(exchange);
    
    // 一些非关键操作
    ...
	
}

public void handleRequest(final Exchange exchange) {
    Code code = exchange.getRequest().getCode();
    switch (code) {
        case GET:	handleGET(new CoapExchange(exchange, this)); break;
        case POST:	handlePOST(new CoapExchange(exchange, this)); break;
        case PUT:	handlePUT(new CoapExchange(exchange, this)); break;
        case DELETE: handleDELETE(new CoapExchange(exchange, this)); break;
    }
}

public void handleGET(CoapExchange exchange) {
    // 由CoapExchange返回响应
    exchange.respond(ResponseCode.CONTENT, msg);
}

public void respond(ResponseCode code, String payload) {

    // 生成响应并赋值
    Response response = new Response(code);
    response.setPayload(payload);
    response.getOptions().setContentFormat(MediaTypeRegistry.TEXT_PLAIN);
    
    // 调用同名函数
    respond(response);
    
}

public void respond(Response response) {

    // 参数校验
    ...
    
    // 设置Response属性
    ...
    
    // 检查关系
    resource.checkObserveRelation(exchange, response);

    // 由成员变量Exchange发送响应
    exchange.sendResponse(response);

}

public void sendResponse(Response response) {

    // 设置Response属性
    response.setDestination(request.getSource());
    response.setDestinationPort(request.getSourcePort());
    setResponse(response);
    
    // 由Endpoint发送响应
    endpoint.sendResponse(this, response);

}

public void sendResponse(Exchange exchange, Response response) {
    outbox.sendResponse(exchange, response);
}

public void sendResponse(Exchange exchange, Response response) {

    // 一些非关键操作
    ...
    
    // 匹配器发送响应
    matcher.sendResponse(exchange, response);

    // 消息拦截器发送响应
    for (MessageInterceptor interceptor:interceptors) {
        interceptor.sendResponse(response);
    }
    
    // 真正地发送响应到网络里
    connector.send(Serializer.serialize(response));
    
}