Blobs: Add static utility class for creating blobs (e.g. using blob parts)

src/main/java/org/vectomatic/file/Blobs.java

@@ -0,0 +1,151 @@
+/**********************************************
+ * Copyright (C) 2015 Shaun Ediger
+ * This file is part of lib-gwt-file.
+ *
+ * lib-gwt-file is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * lib-gwt-file is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with lib-gwt-file.  If not, see http://www.gnu.org/licenses/
+ **********************************************/
+/**
+ * Documentation is adapted from W3C spec and content available from
+ * http://developer.mozilla.org under http://creativecommons.org/licenses/by-sa/2.5/
+ */
+package org.vectomatic.file;
+
+import com.google.gwt.core.client.JavaScriptObject;
+import com.google.gwt.core.client.JsArrayMixed;
+import com.google.gwt.typedarrays.client.ArrayBufferNative;
+import com.google.gwt.typedarrays.client.ArrayBufferViewNative;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * Static utility methods pertaining to the creation of native {@link Blob} instances.
+ *
+ * Creation methods (except for  {@link #newBlob()}) accept an iterable of type {@link Object}.
+ * An {@link IllegalArgumentException} will be thrown if an individual element type is not one of the following: {@link String},
+ * {@link ArrayBufferNative}, {@link ArrayBufferViewNative}, or {@link Blob}.
+ *
+ * Pass a content type (e.g. "text/plain;charset=UTF-8") or null to defer to browser default, which is an empty string.
+ *
+ * @author Shaun Ediger
+ */
+public class Blobs {
+
+	private static Set<Class<? extends JavaScriptObject>> acceptableJavaScriptObjectTypes = new HashSet<Class<? extends JavaScriptObject>>(Arrays.asList(ArrayBufferNative.class, ArrayBufferViewNative.class, Blob.class));
+
+	/**
+	 * Creates a {@link Blob} instance consisting of 0 bytes.
+	 *
+	 * @return
+	 */
+	public static Blob newBlob() {
+		return createBlob();
+	}
+
+	public static Blob newBlob(Iterator<Object> blobParts) {
+		return newBlob(blobParts, null);
+	}
+
+	public static Blob newBlob(Iterator<Object> blobParts, String contentType) {
+		List<Object> blobPartsIterable = new ArrayList<Object>();
+		while (blobParts.hasNext()) {
+			blobPartsIterable.add(blobParts.next());
+		}
+		return newBlob(blobPartsIterable, contentType);
+	}
+
+	public static Blob newBlob(Iterable<Object> blobParts) {
+		return newBlob(blobParts, null);
+	}
+
+	public static Blob newBlob(Iterable<Object> blobParts, String contentType) {
+		checkAcceptable(blobParts);
+		if (contentType == null) {
+			return createBlob(createBlobPartsArray(blobParts));
+		} else {
+			return createBlob(createBlobPartsArray(blobParts), contentType);
+		}
+	}
+
+	private static native Blob createBlob() /*-{
+		return new Blob();
+	}-*/;
+
+	private static native Blob createBlob(JsArrayMixed blobParts) /*-{
+		return new Blob(blobParts);
+	}-*/;
+
+	private static native Blob createBlob(JsArrayMixed blobParts, String contentType) /*-{
+		return new Blob(blobParts, {type: contentType});
+	}-*/;
+
+	private static JsArrayMixed createBlobPartsArray(Iterable<Object> blobParts) {
+		JsArrayMixed blobPartsArray = createBlobPartsArray();
+		for (Object object : blobParts) {
+			if (object instanceof String) {
+				blobPartsArray.push((String) object);
+			} else if (object instanceof JavaScriptObject) {
+				blobPartsArray.push((JavaScriptObject) object);
+			} else {
+				// shouldn't happen if we correctly perform type checking
+				throw new IllegalArgumentException();
+			}
+		}
+		return blobPartsArray;
+	}
+
+	private static native JsArrayMixed createBlobPartsArray() /*-{
+		return [];
+	}-*/;
+
+	private static void checkAcceptable(Iterable<Object> blobParts) {
+		if (!isAcceptableBlobParts(blobParts)) {
+			throw new IllegalArgumentException();
+		}
+	}
+
+	private static boolean isAcceptableBlobParts(Iterable<Object> blobParts) {
+		for (Object object : blobParts) {
+			if (isAcceptableBlobPart(object)) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	private static boolean isAcceptableBlobPart(Object part) {
+		if (part instanceof String) {
+			return true;
+		}
+		for (Class clazz : acceptableJavaScriptObjectTypes) {
+			if (isInstanceOf(clazz, part)) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	private static <T> boolean isInstanceOf(Class<T> type, Object object) {
+		try {
+			T objectAsType = (T) object;
+		} catch (ClassCastException exception) {
+			return false;
+		}
+		return true;
+	}
+}