Load GeoJSON file in OpenLayers 3?

Before, to load my .geojson, I had a php file who generated the code :

var vector_limite_comm_white = new ol.layer.Vector({
    source: new ol.source.GeoJSON({
        url: 'geojson1.php',
        defaultProjection :'EPSG:4326', projection: 'EPSG:3857'
    }), 
    name: 'NAME 1',
    style: style_white()
})

After, I tried to directly load my geojson file, so I wrote :

var vector_name1    = new ol.layer.Vector({
    source: new ol.source.Vector ({
        url: 'data/json/file1.geojson',
        defaultProjection :'EPSG:4323', projection: 'EPSG:3857'

    }),
    name: 'NAME 1',
    style: style_white()
})

In firebug, at onload event, I saw my geojson file was loaded correctly but, it doesn't appear in my map. So I tried an other method like that :

var test = 'data/json/file1.geojson';
var vectorSource = new ol.source.Vector({
    features: (new ol.format.GeoJSON()).readFeature(test)
}); 
var vector_overlay = new ol.layer.Vector({
    source: vectorSource,
    style: new ol.style.Style(style_white()
});

It's not a good method too.

Do you have some explications?

Answer

You must have a issu with your projection. Try getting the extent of your json layer :

layer.getSource().getExtent();