mqtt服务器采用activemq实现。

1. 首先配置activemq支持websocket.
   具体配置，请点击activemq官网配置。
2. 编写客户端页面，引入Paho官方客户端js库。
   具体配置，请点击查看
   贴出关键代码如下：

// Create a client instance
//注意不要在client前写var
client = new Paho.MQTT.Client(location.hostname, Number(location.port), "clientId");

// set callback handlers
client.onConnectionLost = onConnectionLost;
client.onMessageArrived = onMessageArrived;

// connect the client
client.connect({onSuccess:onConnect});


// called when the client connects
function onConnect() {
  // Once a connection has been made, make a subscription and send a message.
  console.log("onConnect");
  client.subscribe("World");
  message = new Paho.MQTT.Message("Hello");
  message.destinationName = "World";
  client.send(message);
}

// called when the client loses its connection
function onConnectionLost(responseObject) {
  if (responseObject.errorCode !== 0) {
    console.log("onConnectionLost:"+responseObject.errorMessage);
  }
}

// called when a message arrives
function onMessageArrived(message) {
  console.log("onMessageArrived:"+message.payloadString);
}

注意不要在client前写var
否则你可能会出现一下错误：

https://www.eclipse.org/forums/index.php/t/1068818/