Coap协议介绍，及其开源实现Californium实战

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"){@Overridepublic void handleGET(CoapExchange exchange) {handlePOST(exchange);};@Overridepublic void handlePOST(CoapExchange exchange) { //1System.out.println(exchange.getRequestOptions().getUriQueryString());System.out.println(exchange.getRequestText().length());exchange.respond("asdfasdf");super.handlePOST(exchange);}}.add(new CoapResource("lenovo"){@Overridepublic void handlePOST(CoapExchange exchange) {  //2int 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() {@Overridepublic void onLoad(CoapResponse response) {System.out.println(Utils.prettyPrint(response));countDown.countDown();}@Overridepublic 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