springboot框架下，设置coap服务器，包括发送端，接收端，coap端口，并设置JSON格式，请写出完整代码，包含依赖项、import语句 以及注释

以下是基于Spring Boot框架的CoAP服务器的完整代码，包括发送端、接收端以及JSON格式设置：

1. 添加依赖项

在pom.xml文件中添加以下依赖项：

<dependency>
    <groupId>org.eclipse.californium</groupId>
    <artifactId>californium-core</artifactId>
    <version>2.0.0-M8</version>
</dependency>
<dependency>
    <groupId>org.eclipse.californium</groupId>
    <artifactId>californium-element-android</artifactId>
    <version>2.0.0-M8</version>
</dependency>

2. 编写CoAP发送端

import org.eclipse.californium.core.CoapClient;
import org.eclipse.californium.core.coap.MediaTypeRegistry;
import org.eclipse.californium.core.coap.Request;
import org.eclipse.californium.core.coap.Response;
import org.springframework.stereotype.Component;

@Component
public class CoapSender {

    public void sendMessage(String uri, String message) {
        CoapClient client = new CoapClient(uri);
        Request request = new Request(Request.POST);
        request.getOptions().setContentFormat(MediaTypeRegistry.APPLICATION_JSON);
        request.setPayload(message.getBytes());
        Response response = client.advanced(request);
        System.out.println("Response Code: " + response.getCode());
        System.out.println("Response Text: " + response.getResponseText());
    }
}

3. 编写CoAP接收端

import org.eclipse.californium.core.CoapResource;
import org.eclipse.californium.core.CoapServer;
import org.eclipse.californium.core.coap.MediaTypeRegistry;
import org.eclipse.californium.core.coap.Request;
import org.eclipse.californium.core.coap.Response;
import org.springframework.stereotype.Component;

@Component
public class CoapReceiver extends CoapServer {

    public CoapReceiver() {
        add(new CoapResource("hello") {
            @Override
            public void handlePOST(CoapExchange exchange) {
                Request request = exchange.getRequest();
                System.out.println("Request Payload: " + new String(request.getPayload()));
                Response response = new Response(ResponseCode.CREATED);
                response.setPayload("Hello, CoAP!".getBytes());
                response.getOptions().setContentFormat(MediaTypeRegistry.APPLICATION_JSON);
                exchange.respond(response);
            }
        });
    }
}

4. 配置CoAP端口和JSON格式

在application.properties中添加以下配置：

# CoAP server port
coap.port=5683
# JSON format
spring.jackson.serialization.indent_output=true
spring.jackson.serialization.write_dates_as_timestamps=false
spring.jackson.serialization.fail_on_empty_beans=false

5. 运行应用程序

在Spring Boot应用程序的启动类中，添加以下代码：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class MyApplication {

    @Autowired
    private CoapReceiver coapReceiver;

    public static void main(String[] args) {
        SpringApplication.run(MyApplication.class, args);
    }

    // Start CoAP server
    @PostConstruct
    public void startCoapServer() {
        coapReceiver.start();
    }

    // Stop CoAP server
    @PreDestroy
    public void stopCoapServer() {
        coapReceiver.stop();
    }
}

现在，您可以使用CoapSender类向CoAP server发送POST请求，并使用CoapReceiver类接收请求并返回响应。