GeoTools GML parser sorted features collection

Question

I am using the following code to parse GML file in java:

File gmlFile = new File("path/to/gml/file");    
InputStream gmlInStream = new FileInputStream(gmlFile);
GML gml = new GML(Version.WFS1_0);
SimpleFeatureCollection featureCollection = gml.decodeFeatureCollection(gmlInStream);
SimpleFeatureIterator iterator = featureCollection.features();
while (iterator.hasNext()) {
       SimpleFeature feature = iterator.next();
       //Do something with the feature
}
iterator.close();

I need to have the returned features collection be sorted by a specific feature's attribute. How to do that?

Answer 1

You need to provide a SortBy to your Query object.

So for example the following code sorts the US States dataset by population (PERSONS):

    URL u = TestData.url("shapes/statepop.shp");
    FileDataStore store = FileDataStoreFinder.getDataStore(u);
    SimpleFeatureType schema = store.getSchema();
    Query query = new Query(schema.getTypeName(), Filter.INCLUDE, 
         new String[] { "STATE_NAME", "PERSONS", "WORKERS" });
    FilterFactory2 ff = CommonFactoryFinder.getFilterFactory2();
    query.setSortBy(new SortBy[] { ff.sort("PERSONS", SortOrder.ASCENDING) });
    SimpleFeatureCollection features = store.getFeatureSource().getFeatures(query);
    try (SimpleFeatureIterator itr = features.features()) {
      while (itr.hasNext()) {
        SimpleFeature feature = itr.next();
        System.out.println(feature.getAttribute("STATE_NAME") + "\t" + feature.getAttribute("PERSONS"));
      }
    }

Or if, as in your case, you have a FeatureCollection and no FeatureSource you can wrap them using the DataUtilities class:

File gmlFile = new File("/home/ian/Downloads/states.xml");
InputStream gmlInStream = new FileInputStream(gmlFile);
GML gml = new GML(Version.WFS1_0);
features = gml.decodeFeatureCollection(gmlInStream);
query = new Query();
query.setSortBy(new SortBy[] { ff.sort("name", SortOrder.DESCENDING) });
features = DataUtilities.source(features).getFeatures(query);
try (SimpleFeatureIterator itr = features.features()) {
  while (itr.hasNext()) {
    SimpleFeature feature = itr.next();
    System.out.println(feature.getAttribute("name") + "\t" + feature.getAttribute("pop_2018"));
  }
}