Coap协议介绍，及其开源实现Californium实战

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/ty497122758/article/details/77387861

物联网Coap协议介绍

Coap（Constrained Application Protocol）是一种特殊的Web协议用在不可靠的设备或者网络，这些设备一般是只有8-bit ROM或RAM的微控制器，这个协议主要用于点到点（machain-to-machain）应用，例如：小电量设备、智能设备，同时支持组播。coap和http类似，我们可以把coap看成http的缩小版，用于小存储不可靠的环境

在各设备间采用request/response的互联模式，有uri的概念(coap://ip:port/path/path/path?p1=v2&p2=v2)

有互联网媒体类型的概念，如下图：

同时也提供：GET、POST、PUT、DELETE四种请求类型

Coap是基于二进制的协议，header只有4个字节，非常紧凑

Californium开源实现

Coap是基于UDP的应用层，但是Californium实现了coap udp和tcp两种传输层协议，单次请求传输限制在1M以内

maven依赖

<dependencies>
	<dependency>
		<groupId>org.eclipse.californium</groupId>
		<artifactId>californium-core</artifactId>
		<version>2.0.0-M3</version>
	</dependency>
	<dependency>
		<groupId>org.eclipse.californium</groupId>
		<artifactId>element-connector</artifactId>
		<version>2.0.0-M3</version>
	</dependency>
	<dependency>
	    <groupId>org.eclipse.californium</groupId>
	    <artifactId>scandium</artifactId>
	    <version>2.0.0-M3</version>
	</dependency>
</dependencies>

服务端示例

package soap;

import java.net.InetSocketAddress;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;

import org.eclipse.californium.core.CoapResource;
import org.eclipse.californium.core.CoapServer;
import org.eclipse.californium.core.network.CoapEndpoint;
import org.eclipse.californium.core.network.config.NetworkConfig;
import org.eclipse.californium.core.server.resources.CoapExchange;
import org.eclipse.californium.elements.tcp.TcpServerConnector;

public class Server {
	
	private static AtomicInteger count = new AtomicInteger();

	public static void main(String[] args) {
		
		final CoapServer server = new CoapServer();
		
		//默认就是ucp实现传输层
		server.addEndpoint(new CoapEndpoint(new InetSocketAddress("127.0.0.1", 5683)));
		
		//加入tcp实现传输层
		server.addEndpoint(new CoapEndpoint(
				new TcpServerConnector(new InetSocketAddress("127.0.0.1", 5683), 4, 20000),
				NetworkConfig.getStandard()));
		
		//可以加入dtls支持，也就是coaps
//		server.addEndpoint(new CoapEndpoint(
//				new DTLSConnector(), //这里只是抛砖引玉，需要构建DtlsConnectorConfig
//				NetworkConfig.getStandard()));
		
		server.add(new CoapResource("tuyou"){
			@Override
			public void handleGET(CoapExchange exchange) {
				handlePOST(exchange);
			};
			@Override
			public void handlePOST(CoapExchange exchange) { //1
				System.out.println(exchange.getRequestOptions().getUriQueryString());
				System.out.println(exchange.getRequestText().length());
				exchange.respond("asdfasdf");
				super.handlePOST(exchange);
			}
		}.add(new CoapResource("lenovo"){
			@Override
			public void handlePOST(CoapExchange exchange) {  //2
				int c = count.incrementAndGet();
				if(c % 10000 == 0){
					System.out.println(c);
				}
				exchange.respond(String.valueOf(c));
				super.handlePOST(exchange);
			}
		}));
		Executors.newSingleThreadExecutor().execute(() -> {
			server.start();
		});
	}
}

当用户请求url为：coap://localhost:5683/tuyou?p1=v1时，是响应1处的函数

当用户请求url为：coap://localhost:5683/tuyou/lenovo?p1=v1时，是响应2处的函数

客户端示例

package soap;

import java.time.Clock;
import java.util.concurrent.CountDownLatch;

import org.eclipse.californium.core.CoapClient;
import org.eclipse.californium.core.CoapHandler;
import org.eclipse.californium.core.CoapResponse;
import org.eclipse.californium.core.Utils;
import org.eclipse.californium.core.coap.MediaTypeRegistry;

public class Client {

	public static void main(String[] args) throws InterruptedException {
		
		int count = 100;
		CountDownLatch countDown = new CountDownLatch(count);
		long start = Clock.systemUTC().millis();
		CoapClient client = new CoapClient("coap://127.0.0.1:5683/tuyou/lenovo?appKey=zq6NDc3sb6QmoQF1&appSecret=PosmJNUoMLD777Nf7tlu");
		for(int i = 0; i < count; i++){
			
			client.post(new CoapHandler() {
				
				@Override
				public void onLoad(CoapResponse response) {
					System.out.println(Utils.prettyPrint(response));
					countDown.countDown();
				}
				
				@Override
				public void onError() {
					
				}
			}, "payload message", MediaTypeRegistry.TEXT_PLAIN);
		}
		countDown.await();
		long end = Clock.systemUTC().millis();
		System.out.println(end - start);
	}
}

提示：示例代码需要用java8运行，否则有些语法会报错

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