HADOOP-19131. Assist reflection IO with WrappedOperations class

Change-Id: Ic29643e8844115ab5938cf041dac02e5b528586f

Author: steveloughran

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/WrappedOperations.java

@@ -0,0 +1,80 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ */
+
+package org.apache.hadoop.io;
+
+import java.io.IOException;
+import java.util.Map;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+import org.apache.hadoop.fs.FSDataInputStream;
+import org.apache.hadoop.fs.FileStatus;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.fs.FutureDataInputStreamBuilder;
+import org.apache.hadoop.util.functional.FutureIO;
+
+import static org.apache.hadoop.fs.Options.OpenFileOptions.FS_OPTION_OPENFILE_READ_POLICY;
+
+/**
+ * Reflection-friendly access to APIs which are not available in
+ * some of the older Hadoop versions which libraries still
+ * compile against.
+ * <p>
+ * The intent is to avoid the need for complex reflection operations
+ * including wrapping of parameter classes, direct instatiation of
+ * new classes etc.
+ */
+@InterfaceAudience.Public
+@InterfaceStability.Evolving
+public final class WrappedOperations {
+
+  private WrappedOperations() {
+  }
+
+  /**
+   * OpenFile assistant, easy reflection-based access to
+   * {@link FileSystem#openFile(org.apache.hadoop.fs.Path)}.
+   * @param fs filesystem
+   * @param path path
+   * @param policy read policy
+   * @param status optional file status
+   * @param options nullable map of other options
+   * @return an opened file
+   * @throws IOException for any failure.
+   */
+  public static FSDataInputStream openFile(final FileSystem fs,
+      final org.apache.hadoop.fs.Path path,
+      final String policy,
+      final FileStatus status,
+      final Map<String, String> options) throws IOException {
+    final FutureDataInputStreamBuilder builder = fs.openFile(path);
+    if (policy != null) {
+      builder.opt(FS_OPTION_OPENFILE_READ_POLICY, policy);
+    }
+    if (status != null) {
+      builder.withFileStatus(status);
+    }
+    if (options != null) {
+      // add all the options map entries
+      options.forEach(builder::opt);
+    }
+    // wait for the opening.
+    return FutureIO.awaitFuture(builder.build());
+  }
+}