Expose FileSystem.Exists API (#909)

src/csharp/Microsoft.Spark.E2ETest/Hadoop/FileSystemTests.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System.IO;
+using System.Linq;
 using Microsoft.Spark.Hadoop.Fs;
 using Microsoft.Spark.Sql;
 using Microsoft.Spark.UnitTest.TestUtils;
@@ -52,5 +53,30 @@ public void TestDelete()
 
             Assert.False(Directory.Exists(path));
         }
+
+        /// <summary>
+        /// Tests that Exists() returns true if the file exist.
+        /// Tests that Exists() returns false if the file doesn't exist.
+        /// </summary>
+        [Fact]
+        public void TestExists()
+        {
+            using FileSystem fs = FileSystem.Get(_spark.SparkContext.HadoopConfiguration());
+
+            using var tempDirectory = new TemporaryDirectory();
+
+            string path = Path.Combine(tempDirectory.Path, "temp-table");
+
+            Assert.False(fs.Exists(path));
+
+            _spark.Range(25).Coalesce(1).Write().Csv(path);
+
+            Assert.True(fs.Exists(path));
+
+            string dataFile = Directory.GetFiles(path, "*.csv").FirstOrDefault();
+
+            Assert.NotNull(dataFile);
+            Assert.True(fs.Exists(dataFile));
+        }
     }
 }

src/csharp/Microsoft.Spark/Hadoop/Fs/FileSystem.cs

@@ -55,6 +55,19 @@ public bool Delete(string path, bool recursive = true)
             return (bool)_jvmObject.Invoke("delete", pathObject, recursive);
         }
 
+        /// <summary>
+        /// Check if a path exists.
+        /// </summary>
+        /// <param name="path">Source path</param>
+        /// <returns>True if the path exists else false.</returns>
+        public bool Exists(string path)
+        {
+            JvmObjectReference pathObject =
+                SparkEnvironment.JvmBridge.CallConstructor("org.apache.hadoop.fs.Path", path);
+
+            return (bool)_jvmObject.Invoke("exists", pathObject);
+        }
+
         public void Dispose() => _jvmObject.Invoke("close");
     }
 }