Convert Kml with multiple features to Geojson

I use this code to convert a kml file with a single feature to a GeoJson file.

String kmlToGeoJson(String fileName)
        throws IOException, ParserConfigurationException, SAXException, XMLStreamException {

    FileInputStream reader = new FileInputStream(fileName);
    PullParser parser = new PullParser(new KMLConfiguration(),reader, SimpleFeature.class);

    FeatureJSON fjson = new FeatureJSON();
    FileWriter tmp = new FileWriter(fileName + ".geojson");
    BufferedWriter writer = new BufferedWriter(tmp);

    SimpleFeature simpleFeature = (SimpleFeature) parser.parse();

    while (simpleFeature != null) {
        fjson.writeFeature(simpleFeature, writer);
        simpleFeature = (SimpleFeature) parser.parse();
    }

    return "success";
}

However, when I use a Kml file with multiple features like this one :

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
  <Document>
    <name>KmlFile</name>
    <Style id="west_campus_style">
      <IconStyle>
        <Icon>
          <href>https://maps.google.com/mapfiles/kml/pushpin/ylw-pushpin.png
          </href>
        </Icon>
      </IconStyle>
      <BalloonStyle>
        <text>$[video]</text>
      </BalloonStyle>
    </Style>
    <Placemark>
      <name>Google West Campus 1</name>
      <styleUrl>#west_campus_style</styleUrl>
      <ExtendedData>
        <Data name="video">
          <value><![CDATA[<iframe width="480" height="360"
            src="https://www.youtube.com/embed/ZE8ODPL2VPI" frameborder="0"
            allowfullscreen></iframe><br><br>]]></value>
        </Data>
      </ExtendedData>
      <Point>
        <coordinates>-122.0914977709329,37.42390182131783,0</coordinates>
      </Point>
    </Placemark>
    <Placemark>
      <name>Google West Campus 2</name>
      <styleUrl>#west_campus_style</styleUrl>
      <ExtendedData>
        <Data name="video">
          <value><![CDATA[<iframe width="480" height="360"
            src="https://www.youtube.com/embed/nb4gvrNrDWw" frameborder="0"
            allowfullscreen></iframe><br><br>]]></value>
        </Data>
      </ExtendedData>
      <Point>
        <coordinates>-122.0926995893311,37.42419403634421,0</coordinates>
      </Point>
    </Placemark>
    <Placemark>
      <name>Google West Campus 3</name>
      <styleUrl>#west_campus_style</styleUrl>
      <ExtendedData>
        <Data name="video">
          <value><![CDATA[<iframe width="480" height="360"
            src="https://www.youtube.com/embed/0hhiEjf7_NA" frameborder="0"
            allowfullscreen></iframe><br><br>]]></value>
        </Data>
      </ExtendedData>
      <Point>
        <coordinates>-122.0922532985281,37.42301710721216,0</coordinates>
      </Point>
    </Placemark>
  </Document>
</kml>

I get this Geojson file :

{ "type":"Feature",
         "geometry":{
                   "type":"Point",
                   "coordinates":[-122.0915,37.4239,0.0]},
         "properties":{"name":"Google West Campus 1",
                      "visibility":true,
                      "open":true,
                      "Style":"FeatureTypeStyleImpl[ name=name, [], rules=<1>                   (<RuleImpl> null\n)]"},
         "id":"fid--579a589e_150ad9a2e4f_-8000"
           }
{"type":"Feature",
"geometry":{
            "type":"Point",
            "coordinates":[-122.0927,37.4242,0.0]},
"properties":{
             "name":"Google West Campus 2",               
             "visibility":true, 
             "open":true,
             "Style":"FeatureTypeStyleImpl[ name=name, [], rules=<1>(<RuleImpl> null\n)]"},
"id":"fid--579a589e_150ad9a2e4f_-7fff"
}
{"type":"Feature",
"geometry":{
           "type":"Point",
           "coordinates":[-122.0923,37.423,0.0]},
"properties":{"name":"Google West Campus 3",
              "visibility":true,
              "open":true,
              "Style":"FeatureTypeStyleImpl[ name=name, [], rules=<1>(<RuleImpl> null\n)]"},
"id":"fid--579a589e_150ad9a2e4f_-7ffe"}
{"type":"Feature",
"properties":          
          {"name":"KmlFile",
          "visibility":true,
          "open":true,
         "name":"KmlFile",
         "Feature":"[]"},
"id":"fid--579a589e_150ad9a2e4f_-7ffd"}

It's like the whole kml file is considered a Single feature, with no comma between the features. How do I get it to consider the whole file as a Multiple Feature File I tried replacing SimpleFeature.class with SimpleFeatureCollection.class, buth the returned Geojson file is empty then.

I think that you need something like this to produce a FeatureCollection:

        FileInputStream reader = new FileInputStream(args[0]);
        PullParser parser = new PullParser(new KMLConfiguration(), reader, SimpleFeature.class);

        
        FileWriter tmp = new FileWriter(args[0] + ".geojson");
        BufferedWriter writer = new BufferedWriter(tmp);
        ArrayList<SimpleFeature> features = new ArrayList<>();
        SimpleFeature simpleFeature = (SimpleFeature) parser.parse();
        while (simpleFeature != null) {
            System.out.println(simpleFeature);
            features.add(simpleFeature);
            simpleFeature = (SimpleFeature) parser.parse();
        }
        SimpleFeatureCollection fc = DataUtilities.collection(features);
    GeoJSONDataStoreFactory fac = new GeoJSONDataStoreFactory();
    Map<String, Serializable> params = new HashMap<>();
    params.put(GeoJSONDataStoreFactory.URL_PARAM.key, url);
    DataStore ds = fac.createNewDataStore(params);
    store.createSchema(schema);
    SimpleFeatureSource featureSource = null;
    try {
        featureSource = ds.getFeatureSource(schema.getTypeName());
    } catch (IOException e1) {
        log.log(Level.INFO, "Didn't get a featureSource", e1);
        System.exit();
    }
    SimpleFeatureStore store = (SimpleFeatureStore) featureSource;

    store.addFeatures(ds.getFeatureSource().getFeatures());

Updated 6/9/22

gt-geojson-store is now the preferred way to deal with GeoJSON input and output.