HADOOP-16247. NPE in FsUrlConnection. Contributed by Karthik Palanisamy.

(cherry picked from commit d4c8858586eeed2820f3ab21da79603b52c64594)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FsUrlConnection.java

@@ -19,6 +19,7 @@ package org.apache.hadoop.fs;
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.net.URI;
 import java.net.URISyntaxException;
 import java.net.URL;
 import java.net.URLConnection;
@@ -56,8 +57,18 @@ class FsUrlConnection extends URLConnection {
     Preconditions.checkState(is == null, "Already connected");
     try {
       LOG.debug("Connecting to {}", url);
-      FileSystem fs = FileSystem.get(url.toURI(), conf);
-      is = fs.open(new Path(url.toURI()));
+      URI uri = url.toURI();
+      FileSystem fs = FileSystem.get(uri, conf);
+      // URI#getPath returns null value if path contains relative path
+      // i.e file:root/dir1/file1
+      // So path can not be constructed from URI.
+      // We can only use schema specific part in URI.
+      // Uri#isOpaque return true if path is relative.
+      if(uri.isOpaque() && uri.getScheme().equals("file")) {
+        is = fs.open(new Path(uri.getSchemeSpecificPart()));
+      } else {
+        is = fs.open(new Path(uri));
+      }
     } catch (URISyntaxException e) {
       throw new IOException(e.toString());
     }

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/TestFsUrlConnectionPath.java

@@ -0,0 +1,107 @@
+/**
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License. See accompanying LICENSE file.
+ */
+package org.apache.hadoop.fs;
+
+import org.apache.hadoop.conf.Configuration;
+import org.junit.AfterClass;
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.io.*;
+import java.net.URL;
+import java.nio.file.Paths;
+
+/**
+ * Test case for FsUrlConnection with relativePath and SPACE.
+ */
+public class TestFsUrlConnectionPath {
+
+  private static final String CURRENT = Paths.get("").toAbsolutePath()
+      .toString();
+  private static final String ABSOLUTE_PATH = "file:" + CURRENT + "/abs.txt";
+  private static final String RELATIVE_PATH = "file:relative.txt";
+  private static final String ABSOLUTE_PATH_W_SPACE = "file:"
+      + CURRENT + "/abs 1.txt";
+  private static final String RELATIVE_PATH_W_SPACE = "file:relative 1.txt";
+  private static final String ABSOLUTE_PATH_W_ENCODED_SPACE =
+      "file:" + CURRENT + "/abs%201.txt";
+  private static final String RELATIVE_PATH_W_ENCODED_SPACE =
+      "file:relative%201.txt";
+  private static final String DATA = "data";
+  private static final Configuration CONFIGURATION = new Configuration();
+
+
+  @BeforeClass
+  public static void initialize() throws IOException{
+    write(ABSOLUTE_PATH.substring(5), DATA);
+    write(RELATIVE_PATH.substring(5), DATA);
+    write(ABSOLUTE_PATH_W_SPACE.substring(5), DATA);
+    write(RELATIVE_PATH_W_SPACE.substring(5), DATA);
+    URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory());
+  }
+
+  @AfterClass
+  public static void cleanup(){
+    delete(ABSOLUTE_PATH.substring(5));
+    delete(RELATIVE_PATH.substring(5));
+    delete(ABSOLUTE_PATH_W_SPACE.substring(5));
+    delete(RELATIVE_PATH_W_SPACE.substring(5));
+  }
+
+  public static void delete(String path){
+    File file = new File(path);
+    file.delete();
+  }
+
+  public static void write(String path, String data) throws IOException{
+    File file = new File(path);
+    file.createNewFile();
+    FileWriter fw = new FileWriter(file);
+    fw.write(data);
+    fw.close();
+  }
+
+  public static int readStream(String path) throws Exception{
+    URL url = new URL(path);
+    InputStream is = url.openStream();
+    return is.available();
+  }
+
+
+  @Test
+  public void testAbsolutePath() throws Exception{
+    int length = readStream(ABSOLUTE_PATH);
+    Assert.assertTrue(length > 1);
+  }
+
+  @Test
+  public void testRelativePath() throws Exception{
+    int length = readStream(RELATIVE_PATH);
+    Assert.assertTrue(length > 1);
+  }
+
+  @Test
+  public void testAbsolutePathWithSpace() throws Exception{
+    int length = readStream(ABSOLUTE_PATH_W_ENCODED_SPACE);
+    Assert.assertTrue(length > 1);
+  }
+
+  @Test
+  public void testRelativePathWithSpace() throws Exception{
+    int length = readStream(RELATIVE_PATH_W_ENCODED_SPACE);
+    Assert.assertTrue(length > 1);
+  }
+
+}