getObjectUrl: add new api to get object URL. (#507)

The URL is only useful to retrieve the object's data if the object has
public read permissions.

Fixes #502

Author: balamurugana

api/src/main/java/io/minio/MinioClient.java

@@ -1142,6 +1142,39 @@ public ObjectStat statObject(String bucketName, String objectName)
   }
 
 
+  /**
+   * Gets object's URL in given bucket.  The URL is ONLY useful to retrieve the object's data if the object has
+   * public read permissions.
+   *
+   * <p><b>Example:</b>
+   * <pre>{@code String url = minioClient.getObjectUrl("my-bucketname", "my-objectname");
+   * System.out.println(url); }</pre>
+   *
+   * @param bucketName Bucket name.
+   * @param objectName Object name in the bucket.
+   *
+   * @return string contains URL to download the object.
+   *
+   * @throws InvalidBucketNameException  upon invalid bucket name is given
+   * @throws NoResponseException         upon no response from server
+   * @throws IOException                 upon connection error
+   * @throws XmlPullParserException      upon parsing response xml
+   * @throws ErrorResponseException      upon unsuccessful execution
+   * @throws InternalException           upon internal library error
+   */
+  public String getObjectUrl(String bucketName, String objectName)
+    throws InvalidBucketNameException, NoSuchAlgorithmException, InsufficientDataException, IOException,
+           InvalidKeyException, NoResponseException, XmlPullParserException, ErrorResponseException,
+           InternalException {
+    updateRegionCache(bucketName);
+    String region = BucketRegionCache.INSTANCE.region(bucketName);
+
+    Request request = createRequest(Method.GET, bucketName, objectName, region, null, null, null, null, 0);
+    HttpUrl url = request.httpUrl();
+    return url.toString();
+  }
+
+
   /**
    * Gets entire object's data as {@link InputStream} in given bucket. The InputStream must be closed
    * after use else the connection will remain open.

api/src/test/java/io/minio/MinioClientTest.java

@@ -182,6 +182,18 @@ public void testPresignGetObject()
     assertEquals(presignedObjectUrl.isEmpty(), false);
   }
 
+  @Test
+  public void testGetObjectUrl()
+    throws NoSuchAlgorithmException, InvalidKeyException, IOException, XmlPullParserException, MinioException {
+    MockWebServer server = new MockWebServer();
+    server.start();
+
+    // get request
+    MinioClient client = new MinioClient(server.url(""));
+    String objectUrl = client.getObjectUrl(BUCKET, "key");
+    assertEquals(objectUrl.isEmpty(), false);
+  }
+
   @Test
   public void testGetObject()
     throws NoSuchAlgorithmException, InvalidKeyException, IOException, XmlPullParserException, MinioException {