AWS Creating new files from an s3 object using JAVA getting error

Question

I have a shape file and i need to read the shape file from my java code. I used below code for reading shape file.

public class App {
    public static void main(String[] args) {
        File file = new File("C:\\Test\\sample.shp");
        Map<String, Object> map = new HashMap<>();//
        try {
            map.put("url", URLs.fileToUrl(file));
            DataStore dataStore = DataStoreFinder.getDataStore(map);
            String typeName = dataStore.getTypeNames()[0];
            SimpleFeatureSource source = dataStore.getFeatureSource(typeName);
            SimpleFeatureCollection collection = source.getFeatures();

            try (FeatureIterator<SimpleFeature> features = collection.features()) {
                while (features.hasNext()) {
                    SimpleFeature feature = features.next();
                    SimpleFeatureType schema = feature.getFeatureType();
                    Class<?> geomType = schema.getGeometryDescriptor().getType().getBinding();

                    String type = "";
                    if (Polygon.class.isAssignableFrom(geomType) || MultiPolygon.class.isAssignableFrom(geomType)) {

                        MultiPolygon geom = (MultiPolygon) feature.getDefaultGeometry();
                        type = "Polygon";
                        if (geom.getNumGeometries() > 1) {
                            type = "MultiPolygon";
                        }
                    } else if (LineString.class.isAssignableFrom(geomType)
                            || MultiLineString.class.isAssignableFrom(geomType)) {
                    } else {

                    }
                    System.out.println(feature.getDefaultGeometryProperty().getValue().toString());

                }
            }
        } catch (Exception e) {
            // TODO: handle exception
        }

    }
}

I got the desired output. But my requirement is write an aws lambda function to read shape file. For this 1. I created a Lambda java project of s3 event. I wrote the same code inside the handleRequest. I uploaded the java lambda project as a lanbda function and added one trigger. When I am uploading a .shp file to as s3 bucket lmbda function will automatically invoked. But I am getting an error like below

java.lang.RuntimeException: java.io.FileNotFoundException: /sample.shp (No such file or directory)

I have sample.shp file inside my s3 bucket. I go through below link. How to write an S3 object to a file?

I am getting the same error. I tried to change my code like below

  S3Object object = s3.getObject(new GetObjectRequest(bucket, key)); 
  InputStream objectData = object.getObjectContent();
  map.put("url", objectData );

instead of

File file = new File("C:\\Test\\sample.shp"); 
 map.put("url", URLs.fileToUrl(file));

:-( Now i am getting an error like below

java.lang.NullPointerException

Also I tried the below code

DataStore dataStore = DataStoreFinder.getDataStore(objectData);

instead of

DataStore dataStore = DataStoreFinder.getDataStore(map);

the error was like below

java.lang.ClassCastException: com.amazonaws.services.s3.model.S3ObjectInputStream cannot be cast to java.util.Map

Also I tried to add key directly to the map and also as DataStore object. Everything went wrong..:-(

Is there anyone who can help me? It will be very helpful if someone can do it for me...

Answer 1

The DataStoreFinder.getDataStore method in geotools requires you to provide a map containing a key/value pair with key "url". The value associated with that "url" key needs to be a file URL like "file://host/path/my.shp".

You're trying to insert a Java input stream into the map. That won't work, because it's not a file URL.

The geotools library does not accept http/https URLs (see the geotools code here and here), so you need a file:// URL. That means you will need to download the file from S3 to the local Lambda filesystem and then provide a file:// URL pointing to that local file. To do that, here's Java code that should work:

// get the shape file from S3 to local filesystem
File localshp = new File("/tmp/download.shp");
s3.getObject(new GetObjectRequest(bucket, key), localshp);

// now store file:// URL in the map
map.put("url", localshp.getURI().getURL().toString());

If the geotools library had accepted real URLs (not just file:// URLs) then you could have avoided the download and simply created a time-limited, pre-signed URL for the S3 object and put that URL into the map.

Here's an example of how to do that:

// get current time and add one hour
java.util.Date expiration = new java.util.Date();
long msec = expiration.getTime();
msec += 1000 * 60 * 60;
expiration.setTime(msec);

// request pre-signed URL that will allow bearer to GET the object
GeneratePresignedUrlRequest gpur = new GeneratePresignedUrlRequest(bucket, key);
gpur.setMethod(HttpMethod.GET);
gpur.setExpiration(expiration);

// get URL that will expire in one hour
URL url = s3.generatePresignedUrl(gpur);