Add downloadTo to Blob

Author: Sai Cheemalapati

google-cloud-storage/src/main/java/com/google/cloud/storage/Blob.java

@@ -34,9 +34,15 @@
 import com.google.cloud.storage.spi.v1.StorageRpc;
 import com.google.common.base.Function;
 import com.google.common.io.BaseEncoding;
+
+import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.ObjectInputStream;
 import java.net.URL;
+import java.nio.ByteBuffer;
+import java.nio.channels.Channels;
+import java.nio.channels.WritableByteChannel;
+import java.nio.file.Path;
 import java.security.Key;
 import java.util.Arrays;
 import java.util.List;
@@ -186,6 +192,26 @@ static Storage.BlobGetOption[] toGetOptions(BlobInfo blobInfo, BlobSourceOption.
     }
   }
 
+  /**
+   * Downloads this blob to the given file path.
+   *
+   * @param path destination
+   * @throws IOException upon failure
+   */
+  public void downloadTo(Path path) throws IOException {
+    FileOutputStream outputStream = new FileOutputStream(path.toFile());
+    try (ReadChannel reader = reader()) {
+      WritableByteChannel channel = Channels.newChannel(outputStream);
+      ByteBuffer bytes = ByteBuffer.allocate(64 * 1024);
+      while (reader.read(bytes) > 0) {
+        bytes.flip();
+        channel.write(bytes);
+        bytes.clear();
+      }
+    }
+    outputStream.close();
+  }
+
   /**
    * Builder for {@code Blob}.
    */

google-cloud-storage/src/test/java/com/google/cloud/storage/BlobTest.java

@@ -16,11 +16,14 @@
 
 package com.google.cloud.storage;
 
+import static org.easymock.EasyMock.anyObject;
 import static org.easymock.EasyMock.capture;
 import static org.easymock.EasyMock.createMock;
+import static org.easymock.EasyMock.createNiceMock;
 import static org.easymock.EasyMock.createStrictMock;
 import static org.easymock.EasyMock.eq;
 import static org.easymock.EasyMock.expect;
+import static org.easymock.EasyMock.getCurrentArguments;
 import static org.easymock.EasyMock.replay;
 import static org.easymock.EasyMock.verify;
 import static org.junit.Assert.assertArrayEquals;
@@ -43,11 +46,15 @@
 import com.google.common.io.BaseEncoding;
 
 import org.easymock.Capture;
+import org.easymock.IAnswer;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 
+import java.io.File;
 import java.net.URL;
+import java.nio.ByteBuffer;
+import java.nio.file.Files;
 import java.security.Key;
 import java.util.List;
 import java.util.Map;
@@ -517,4 +524,34 @@ public void testBuilder() {
     assertNull(blob.getUpdateTime());
     assertTrue(blob.isDirectory());
   }
+
+  @Test
+  public void testDownloadTo() throws Exception {
+    final byte[] expected = {1, 2};
+
+    initializeExpectedBlob(2);
+    ReadChannel channel = createNiceMock(ReadChannel.class);
+    expect(storage.getOptions()).andReturn(mockOptions);
+    expect(storage.reader(BLOB_INFO.getBlobId())).andReturn(channel);
+    replay(storage);
+    // First read should return 2 bytes.
+    expect(channel.read(anyObject(ByteBuffer.class)))
+        .andAnswer(new IAnswer<Integer>() {
+          @Override
+          public Integer answer() throws Throwable {
+            // Modify the argument to match the expected behavior of `read`.
+            ((ByteBuffer) getCurrentArguments()[0]).put(expected);
+            return 2;
+          }
+        });
+    // Second read should return 0 bytes.
+    expect(channel.read(anyObject(ByteBuffer.class))).andReturn(0);
+    replay(channel);
+    initializeBlob();
+
+    File file = File.createTempFile("blob", ".tmp");
+    blob.downloadTo(file.toPath());
+    byte actual[] = Files.readAllBytes(file.toPath());
+    assertArrayEquals(expected, actual);
+  }
 }