How to list files in S3 bucket using Spark Session?

Question

Is it possible to list all of the files in given S3 path (ex: s3://my-bucket/my-folder/*.extension) using a SparkSession object?

Answer 1

You can use Hadoop API for accessing files on S3 (Spark uses it as well):

import java.net.URI
import org.apache.hadoop.fs.FileSystem
import org.apache.hadoop.fs.Path
import org.apache.hadoop.conf.Configuration

val path = "s3://somebucket/somefolder"
val fileSystem = FileSystem.get(URI.create(path), new Configuration())
val it = fileSystem.listFiles(new Path(path), true)
while (it.hasNext()) {
  ...
}

Answer 2

Approach 1

For pyspark users, I've translated Michael Spector's answer (I'll leave it to you to decide if using this is a good idea):

sc = spark.sparkContext
myPath = f's3://my-bucket/my-prefix/'
javaPath = sc._jvm.java.net.URI.create(myPath)
hadoopPath = sc._jvm.org.apache.hadoop.fs.Path(myPath)
hadoopFileSystem = sc._jvm.org.apache.hadoop.fs.FileSystem.get(javaPath, sc._jvm.org.apache.hadoop.conf.Configuration())
iterator = hadoopFileSystem.listFiles(hadoopPath, True)

s3_keys = []
while iterator.hasNext():
    s3_keys.append(iterator.next().getPath().toUri().getRawPath())    

s3_keys now holds all file keys found at my-bucket/my-prefix

Approach 2 Here is an alternative that I found (hat tip to @forgetso):

myPath = 's3://my-bucket/my-prefix/*'
hadoopPath = sc._jvm.org.apache.hadoop.fs.Path(myPath)
hadoopFs = hadoopPath.getFileSystem(sc._jvm.org.apache.hadoop.conf.Configuration())
statuses = hadoopFs.globStatus(hadoopPath)

for status in statuses:
  status.getPath().toUri().getRawPath()
  # Alternatively, you can get file names only with:
  # status.getPath().getName()

Approach 3 (incomplete!)

The two approaches above do not use the Spark parallelism mechanism that would be applied on a distributed read. That logic looks private though. See parallelListLeafFiles here. I have not found a way to compel pyspark do to a distributed ls on s3 without also reading the file contents. I tried to use py4j to instantiate an InMemoryFileIndex, but can't get the incantation right. Here is what I have so far if someone wants to pick it up from here:

myPath = f's3://my-bucket/my-path/'
paths = sc._gateway.new_array(sc._jvm.org.apache.hadoop.fs.Path, 1)
paths[0] = sc._jvm.org.apache.hadoop.fs.Path(myPath)

emptyHashMap = sc._jvm.java.util.HashMap()
emptyScalaMap = sc._jvm.scala.collection.JavaConversions.mapAsScalaMap(emptyMap)

# Py4J is not happy with this:
sc._jvm.org.apache.spark.sql.execution.datasources.InMemoryFileIndex(
    spark._jsparkSession, 
    paths, 
    emptyScalaMap, 
    sc._jvm.scala.Option.empty() # Optional None
)