NIO CountBytes example (#975)

gcloud-java-examples/pom.xml

@@ -63,6 +63,10 @@
               <mainClass>com.google.cloud.examples.nio.Stat</mainClass>
               <name>Stat</name>
             </program>
+            <program>
+              <mainClass>com.google.cloud.examples.nio.CountBytes</mainClass>
+              <name>CountBytes</name>
+            </program>
             <program>
               <mainClass>
                 com.google.cloud.examples.resourcemanager.ResourceManagerExample

gcloud-java-examples/src/main/java/com/google/cloud/examples/nio/CountBytes.java

@@ -0,0 +1,102 @@
+/*
+ * Copyright 2016 Google Inc. All Rights Reserved.
+ *
+ * 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.
+ */
+
+package com.google.cloud.examples.nio;
+
+import com.google.common.base.Stopwatch;
+
+import java.io.IOException;
+import java.net.URI;
+import java.nio.ByteBuffer;
+import java.nio.channels.SeekableByteChannel;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * CountBytes will read through the whole file given as input.
+ *
+ * <p>This example shows how to read a file size using NIO.
+ * File.size returns the size of the file as saved in Storage metadata.
+ * This class also shows how to read all of the file's contents using NIO,
+ * and reports how long it took.
+ *
+ * <p>See the README for compilation instructions. Run this code with
+ * {@code target/appassembler/bin/CountBytes <file>}
+ */
+public class CountBytes {
+
+  /**
+   * See the class documentation.
+   */
+  public static void main(String[] args) throws IOException {
+    if (args.length == 0 || args[0].equals("--help")) {
+      help();
+      return;
+    }
+    for (String a : args) {
+      countFile(a);
+    }
+  }
+
+  /**
+   * Print the length of the indicated file.
+   *
+   * <p>This uses the normal Java NIO Api, so it can take advantage of any installed
+   * NIO Filesystem provider without any extra effort.
+   */
+  private static void countFile(String fname) {
+    // large buffers pay off
+    final int bufSize = 50 * 1024 * 1024;
+    try {
+      Path path = Paths.get(new URI(fname));
+      long size = Files.size(path);
+      System.out.println(fname + ": " + size + " bytes.");
+      ByteBuffer buf = ByteBuffer.allocate(bufSize);
+      System.out.println("Reading the whole file...");
+      Stopwatch sw = Stopwatch.createStarted();
+      SeekableByteChannel chan = Files.newByteChannel(path);
+      long total = 0;
+      int readCalls = 0;
+      while (chan.read(buf) > 0) {
+        readCalls++;
+        total += buf.position();
+        buf.flip();
+      }
+      readCalls++; // We must count the last call
+      long elapsed = sw.elapsed(TimeUnit.SECONDS);
+      System.out.println("Read all " + total + " bytes in " + elapsed + "s. " +
+          "(" + readCalls +" calls to chan.read)");
+      if (total != size) {
+        System.out.println("Wait, this doesn't match! We saw " + total + " bytes, " +
+            "yet the file size is listed at " + size + " bytes.");
+      }
+    } catch (Exception ex) {
+      System.out.println(fname + ": " + ex.toString());
+    }
+  }
+
+  private static void help() {
+    String[] help =
+        {"The argument is a <path>",
+         "and we show the length of that file."
+        };
+    for (String s : help) {
+      System.out.println(s);
+    }
+  }
+}

gcloud-java-examples/src/main/java/com/google/cloud/examples/nio/Stat.java

@@ -1,3 +1,19 @@
+/*
+ * Copyright 2016 Google Inc. All Rights Reserved.
+ *
+ * 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.
+ */
+
 package com.google.cloud.examples.nio;
 
 import java.io.IOException;