Universal-Image-Loader源码阅读（29）-BaseImageDownloader

ImageDownLoader的具体实现。

源码：

/** * Provides retrieving of {@link InputStream} of image by URI from network or file system or app resources.<br /> * {@link URLConnection} is used to retrieve image stream from network. * * @author Sergey Tarasevich (nostra13[at]gmail[dot]com) * @since 1.8.0 */public class BaseImageDownloader implements ImageDownloader {/** {@value} */public static final int DEFAULT_HTTP_CONNECT_TIMEOUT = 5 * 1000; // milliseconds/** {@value} */public static final int DEFAULT_HTTP_READ_TIMEOUT = 20 * 1000; // milliseconds/** {@value} */protected static final int BUFFER_SIZE = 32 * 1024; // 32 Kb/** {@value} */protected static final String ALLOWED_URI_CHARS = "@#&=*+-_.,:!?()/~'%";protected static final int MAX_REDIRECT_COUNT = 5;protected static final String CONTENT_CONTACTS_URI_PREFIX = "content://com.android.contacts/";private static final String ERROR_UNSUPPORTED_SCHEME = "UIL doesn't support scheme(protocol) by default [%s]. " + "You should implement this support yourself (BaseImageDownloader.getStreamFromOtherSource(...))";protected final Context context;protected final int connectTimeout;protected final int readTimeout;public BaseImageDownloader(Context context) {this(context, DEFAULT_HTTP_CONNECT_TIMEOUT, DEFAULT_HTTP_READ_TIMEOUT);}public BaseImageDownloader(Context context, int connectTimeout, int readTimeout) {this.context = context.getApplicationContext();this.connectTimeout = connectTimeout;this.readTimeout = readTimeout;}@Overridepublic InputStream getStream(String imageUri, Object extra) throws IOException {switch (Scheme.ofUri(imageUri)) {case HTTP:case HTTPS:return getStreamFromNetwork(imageUri, extra);case FILE:return getStreamFromFile(imageUri, extra);case CONTENT:return getStreamFromContent(imageUri, extra);case ASSETS:return getStreamFromAssets(imageUri, extra);case DRAWABLE:return getStreamFromDrawable(imageUri, extra);case UNKNOWN:default:return getStreamFromOtherSource(imageUri, extra);}}/** * Retrieves {@link InputStream} of image by URI (image is located in the network). * * @param imageUri Image URI * @param extra    Auxiliary object which was passed to {@link DisplayImageOptions.Builder#extraForDownloader(Object) *                 DisplayImageOptions.extraForDownloader(Object)}; can be null * @return {@link InputStream} of image * @throws IOException if some I/O error occurs during network request or if no InputStream could be created for *                     URL. */protected InputStream getStreamFromNetwork(String imageUri, Object extra) throws IOException {//同步获取网络图片HttpURLConnection conn = createConnection(imageUri, extra);int redirectCount = 0;while (conn.getResponseCode() / 100 == 3 && redirectCount < MAX_REDIRECT_COUNT) {conn = createConnection(conn.getHeaderField("Location"), extra);redirectCount++;}InputStream imageStream;try {imageStream = conn.getInputStream();} catch (IOException e) {// Read all data to allow reuse connection (http://bit.ly/1ad35PY)IoUtils.readAndCloseStream(conn.getErrorStream());throw e;}if (!shouldBeProcessed(conn)) {IoUtils.closeSilently(imageStream);throw new IOException("Image request failed with response code " + conn.getResponseCode());}return new ContentLengthInputStream(new BufferedInputStream(imageStream, BUFFER_SIZE), conn.getContentLength());}/** * @param conn Opened request connection (response code is available) * @return <b>true</b> - if data from connection is correct and should be read and processed; *         <b>false</b> - if response contains irrelevant data and shouldn't be processed * @throws IOException */protected boolean shouldBeProcessed(HttpURLConnection conn) throws IOException {return conn.getResponseCode() == 200;}/** * Create {@linkplain HttpURLConnection HTTP connection} for incoming URL * * @param url   URL to connect to * @param extra Auxiliary object which was passed to {@link DisplayImageOptions.Builder#extraForDownloader(Object) *              DisplayImageOptions.extraForDownloader(Object)}; can be null * @return {@linkplain HttpURLConnection Connection} for incoming URL. Connection isn't established so it still configurable. * @throws IOException if some I/O error occurs during network request or if no InputStream could be created for *                     URL. */protected HttpURLConnection createConnection(String url, Object extra) throws IOException {String encodedUrl = Uri.encode(url, ALLOWED_URI_CHARS);HttpURLConnection conn = (HttpURLConnection) new URL(encodedUrl).openConnection();conn.setConnectTimeout(connectTimeout);conn.setReadTimeout(readTimeout);return conn;}/** * Retrieves {@link InputStream} of image by URI (image is located on the local file system or SD card). * * @param imageUri Image URI * @param extra    Auxiliary object which was passed to {@link DisplayImageOptions.Builder#extraForDownloader(Object) *                 DisplayImageOptions.extraForDownloader(Object)}; can be null * @return {@link InputStream} of image * @throws IOException if some I/O error occurs reading from file system */protected InputStream getStreamFromFile(String imageUri, Object extra) throws IOException {//从文件中获取图片String filePath = Scheme.FILE.crop(imageUri);if (isVideoFileUri(imageUri)) {return getVideoThumbnailStream(filePath);} else {BufferedInputStream imageStream = new BufferedInputStream(new FileInputStream(filePath), BUFFER_SIZE);return new ContentLengthInputStream(imageStream, (int) new File(filePath).length());}}@TargetApi(Build.VERSION_CODES.FROYO)private InputStream getVideoThumbnailStream(String filePath) {if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.FROYO) {Bitmap bitmap = ThumbnailUtils.createVideoThumbnail(filePath, MediaStore.Images.Thumbnails.FULL_SCREEN_KIND);if (bitmap != null) {ByteArrayOutputStream bos = new ByteArrayOutputStream();bitmap.compress(CompressFormat.PNG, 0, bos);return new ByteArrayInputStream(bos.toByteArray());}}return null;}/** * Retrieves {@link InputStream} of image by URI (image is accessed using {@link ContentResolver}). * * @param imageUri Image URI * @param extra    Auxiliary object which was passed to {@link DisplayImageOptions.Builder#extraForDownloader(Object) *                 DisplayImageOptions.extraForDownloader(Object)}; can be null * @return {@link InputStream} of image * @throws FileNotFoundException if the provided URI could not be opened */protected InputStream getStreamFromContent(String imageUri, Object extra) throws FileNotFoundException {//从resource中获取图片ContentResolver res = context.getContentResolver();Uri uri = Uri.parse(imageUri);if (isVideoContentUri(uri)) { // video thumbnailLong origId = Long.valueOf(uri.getLastPathSegment());Bitmap bitmap = MediaStore.Video.Thumbnails.getThumbnail(res, origId, MediaStore.Images.Thumbnails.MINI_KIND, null);if (bitmap != null) {ByteArrayOutputStream bos = new ByteArrayOutputStream();bitmap.compress(CompressFormat.PNG, 0, bos);return new ByteArrayInputStream(bos.toByteArray());}} else if (imageUri.startsWith(CONTENT_CONTACTS_URI_PREFIX)) { // contacts photoreturn getContactPhotoStream(uri);}return res.openInputStream(uri);}@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH)protected InputStream getContactPhotoStream(Uri uri) {//从联系人中获取图片ContentResolver res = context.getContentResolver();if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.ICE_CREAM_SANDWICH) {return ContactsContract.Contacts.openContactPhotoInputStream(res, uri, true);} else {return ContactsContract.Contacts.openContactPhotoInputStream(res, uri);}}/** * Retrieves {@link InputStream} of image by URI (image is located in assets of application). * * @param imageUri Image URI * @param extra    Auxiliary object which was passed to {@link DisplayImageOptions.Builder#extraForDownloader(Object) *                 DisplayImageOptions.extraForDownloader(Object)}; can be null * @return {@link InputStream} of image * @throws IOException if some I/O error occurs file reading */protected InputStream getStreamFromAssets(String imageUri, Object extra) throws IOException {//从asset中获取图片String filePath = Scheme.ASSETS.crop(imageUri);return context.getAssets().open(filePath);}/** * Retrieves {@link InputStream} of image by URI (image is located in drawable resources of application). * * @param imageUri Image URI * @param extra    Auxiliary object which was passed to {@link DisplayImageOptions.Builder#extraForDownloader(Object) *                 DisplayImageOptions.extraForDownloader(Object)}; can be null * @return {@link InputStream} of image */protected InputStream getStreamFromDrawable(String imageUri, Object extra) {//从drawable中获取图片String drawableIdString = Scheme.DRAWABLE.crop(imageUri);int drawableId = Integer.parseInt(drawableIdString);return context.getResources().openRawResource(drawableId);}/** * Retrieves {@link InputStream} of image by URI from other source with unsupported scheme. Should be overriden by * successors to implement image downloading from special sources.<br /> * This method is called only if image URI has unsupported scheme. Throws {@link UnsupportedOperationException} by * default. * * @param imageUri Image URI * @param extra    Auxiliary object which was passed to {@link DisplayImageOptions.Builder#extraForDownloader(Object) *                 DisplayImageOptions.extraForDownloader(Object)}; can be null * @return {@link InputStream} of image * @throws IOException                   if some I/O error occurs * @throws UnsupportedOperationException if image URI has unsupported scheme(protocol) */protected InputStream getStreamFromOtherSource(String imageUri, Object extra) throws IOException {throw new UnsupportedOperationException(String.format(ERROR_UNSUPPORTED_SCHEME, imageUri));}private boolean isVideoContentUri(Uri uri) {String mimeType = context.getContentResolver().getType(uri);return mimeType != null && mimeType.startsWith("video/");}private boolean isVideoFileUri(String uri) {String extension = MimeTypeMap.getFileExtensionFromUrl(uri);String mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension);return mimeType != null && mimeType.startsWith("video/");}}