每 X 秒用 mysql 数据更新 google java 地图

Question

I am trying to update markers on a map every X seconds. The map loads fine with the initial data but how to make only the markers refresh (and not the whole map)..
My code is pretty straight forward.. I have good knowledge of php and mysql but I lack enough java knowledge to pull this off.

<script>
  var customLabel = {
    restaurant: {
      label: 'R'
    },
    bar: {
      label: 'B'
    }
  };

    function initMap() {
    var map = new google.maps.Map(document.getElementById('map'), {
      center: new google.maps.LatLng(51.337834, 5.222728),
      zoom: 7
    });
    var infoWindow = new google.maps.InfoWindow;

      downloadUrl('http://myurl.php', function(data) {
        var xml = data.responseXML;
        var markers = xml.documentElement.getElementsByTagName('marker');
        Array.prototype.forEach.call(markers, function(markerElem) {
          var name = markerElem.getAttribute('name');
          var address = markerElem.getAttribute('address');
          var type = markerElem.getAttribute('type');
          var point = new google.maps.LatLng(
              parseFloat(markerElem.getAttribute('lat')),
              parseFloat(markerElem.getAttribute('lng')));

          var infowincontent = document.createElement('div');
          var strong = document.createElement('strong');
          strong.textContent = name
          infowincontent.appendChild(strong);
          infowincontent.appendChild(document.createElement('br'));

          var text = document.createElement('text');
          text.textContent = address
          infowincontent.appendChild(text);
          var icon = customLabel[type] || {};
          var marker = new google.maps.Marker({
            map: map,
            position: point,
            label: icon.label
          });
          marker.addListener('click', function() {
            infoWindow.setContent(infowincontent);
            infoWindow.open(map, marker);
          });
        });
      });
    }



  function downloadUrl(url, callback) {
    var request = window.ActiveXObject ?
        new ActiveXObject('Microsoft.XMLHTTP') :
        new XMLHttpRequest;

    request.onreadystatechange = function() {
      if (request.readyState == 4) {
        request.onreadystatechange = doNothing;
        callback(request, request.status);
      }
    };

    request.open('GET', url, true);
    request.send(null);
  }



  function doNothing() {}
</script>
<script async defer
src="https://maps.googleapis.com/maps/api/js?key=APIKEY&callback=initMap">
</script>

I have a strong feeling I need to the use the setInterval function somewhere.. however I tried this a few times for example by putting it as this little part;

setInterval(function() { 
downloadUrl('http://myurl.p....
}, 5000);

But no luck.. any ideas?

UPDATE

I managed to get it working using the below code.. I don't know if this is the most efficient way.. and now I get extra markers showing a trail.. so I still need a way to first clear all markers before putting the new ones;

    downloadUrl('myurl.php', function(data) {
        var xml = data.responseXML;
        var markers = xml.documentElement.getElementsByTagName('marker');
        Array.prototype.forEach.call(markers, function(markerElem) {
          var name = markerElem.getAttribute('name');
          var address = markerElem.getAttribute('address');
          var type = markerElem.getAttribute('type');
          var point = new google.maps.LatLng(
              parseFloat(markerElem.getAttribute('lat')),
              parseFloat(markerElem.getAttribute('lng')));

          var infowincontent = document.createElement('div');
          var strong = document.createElement('strong');
          strong.textContent = name
          infowincontent.appendChild(strong);
          infowincontent.appendChild(document.createElement('br'));

          var text = document.createElement('text');
          text.textContent = address
          infowincontent.appendChild(text);
          var icon = customLabel[type] || {};
          var marker = new google.maps.Marker({
            map: map,
            position: point,
            label: icon.label
          });
          marker.addListener('click', function() {
            infoWindow.setContent(infowincontent);
            infoWindow.open(map, marker);
          });
        });
},5000); 
      });
    }

Answer 1

You use a lot of variables which you only use once. You cold compress your code a bit. Moreover I added an array for your markers so you can clean them by a function. This function could also be called before you call downloadUrl instead of adding it there:

var myMarkers = [];

downloadUrl('myurl.php', function(data) {
    var xml = data.responseXML;
    clearMarkers();
    var markers = xml.documentElement.getElementsByTagName('marker');
    Array.prototype.forEach.call(markers, function(markerElem) {
        var infowincontent = document.createElement('div');
        var strong = document.createElement('strong');
        strong.textContent = markerElem.getAttribute('name')
        infowincontent.appendChild(strong);
        infowincontent.appendChild(document.createElement('br'));

        var text = document.createElement('text');
        text.textContent = markerElem.getAttribute('address')
        infowincontent.appendChild(text);
        var icon = customLabel[markerElem.getAttribute('type')] || {};
        var marker = new google.maps.Marker({
            map: map,
            position: new google.maps.LatLng(
                parseFloat(markerElem.getAttribute('lat')),
                parseFloat(markerElem.getAttribute('lng')));,
            label: icon.label
        });
        marker.addListener('click', function() {
            infoWindow.setContent(infowincontent);
            infoWindow.open(map, marker);
        });
        myMarkers.push(marker);
    });
}, 5000);

function clearMarkers() {
    for (var i = 0; i < myMarkers.length; i++) {
        myMarkers[i].setMap(null);
    }
    myMarkers.length = 0;
}

Should work.