同樣地，開(kāi)始之前先思考1個(gè)問(wèn)題：
- Glide是怎么實(shí)現(xiàn)那么多資源Model的加載的？比如可以從Url、Asset、FileDescriptor、Uri、File等來(lái)源加載數(shù)據(jù)
1.ModelLoader
Glide的所有數(shù)據(jù)加載都實(shí)現(xiàn)一個(gè)接口ModelLoader<Model, Data>,其中Model類(lèi)型就是來(lái)源的類(lèi)型，Data是加載得到的數(shù)據(jù)類(lèi)型，看下接口的具體源碼,包含一個(gè)內(nèi)部類(lèi)LoadData，和兩個(gè)接口方法，一個(gè)buildLoadData方法用來(lái)構(gòu)造返回一個(gè)LoadData,另外一個(gè)方法handles用來(lái)返回這個(gè)ModelLoader能否處理這個(gè)Model。LoadData這個(gè)類(lèi)里面有三個(gè)字段，一個(gè)sourceKey用來(lái)表示這次下載，一個(gè)DataFetcher用來(lái)獲取不在緩存中的數(shù)據(jù)：
public interface ModelLoader<Model, Data> {
/**
* @param <Data> The type of data that well be loaded.
*/
class LoadData<Data> {
public final Key sourceKey;
public final List<Key> alternateKeys;
public final DataFetcher<Data> fetcher;
public LoadData(@NonNull Key sourceKey, @NonNull DataFetcher<Data> fetcher) {
this(sourceKey, Collections.<Key>emptyList(), fetcher);
}
public LoadData(@NonNull Key sourceKey, @NonNull List<Key> alternateKeys,
@NonNull DataFetcher<Data> fetcher) {
this.sourceKey = Preconditions.checkNotNull(sourceKey);
this.alternateKeys = Preconditions.checkNotNull(alternateKeys);
this.fetcher = Preconditions.checkNotNull(fetcher);
}
}
@Nullable
LoadData<Data> buildLoadData(@NonNull Model model, int width, int height,
@NonNull Options options);
boolean handles(@NonNull Model model);
}
看下Glide里面所有的實(shí)現(xiàn)類(lèi)，這些種類(lèi)就代表了Glide支持從哪些數(shù)據(jù)類(lèi)型下載數(shù)據(jù)：
比如我們看一個(gè)最常用的從http/https uris下載數(shù)據(jù)的UrlUriLoader, 先看它的接口方法handles，如果scheme類(lèi)型是http/https類(lèi)型的就返回true;另外一個(gè)接口方法buildLoadData通過(guò)字段urlloader返回一個(gè)LoadData,還有一個(gè)內(nèi)部工廠類(lèi)StramFactory, UrlUriLoader不建議外面通過(guò)構(gòu)造函數(shù)實(shí)例化，而是通過(guò)這個(gè)工廠類(lèi)的build方法進(jìn)行實(shí)例化。基本上ModelLoader的實(shí)現(xiàn)類(lèi)都是這種設(shè)計(jì)模式。
// UrlUriLoader.java
public class UrlUriLoader<Data> implements ModelLoader<Uri, Data> {
private static final Set<String> SCHEMES = Collections.unmodifiableSet(
new HashSet<>(
Arrays.asList(
"http",
"https"
)
)
);
private final ModelLoader<GlideUrl, Data> urlLoader;
// Public API.
@SuppressWarnings("WeakerAccess")
public UrlUriLoader(ModelLoader<GlideUrl, Data> urlLoader) {
this.urlLoader = urlLoader;
}
@Override
public LoadData<Data> buildLoadData(@NonNull Uri uri, int width, int height,
@NonNull Options options) {
GlideUrl glideUrl = new GlideUrl(uri.toString());
return urlLoader.buildLoadData(glideUrl, width, height, options);
}
@Override
public boolean handles(@NonNull Uri uri) {
return SCHEMES.contains(uri.getScheme());
}
/**
* Loads {@link java.io.InputStream InputStreams} from {@link android.net.Uri Uris} with http
* or https schemes.
*/
public static class StreamFactory implements ModelLoaderFactory<Uri, InputStream> {
@NonNull
@Override
public ModelLoader<Uri, InputStream> build(MultiModelLoaderFactory multiFactory) {
return new UrlUriLoader<>(multiFactory.build(GlideUrl.class, InputStream.class));
}
@Override
public void teardown() {
// Do nothing.
}
}
}
StreamFactory也是實(shí)現(xiàn)一個(gè)工廠接口ModelLoaderFactory,具體看下這個(gè)接口代碼：
// ModelLoaderFactory.java
/**
* An interface for creating a {@link ModelLoader} for a given model type.
*
* @param <T> The type of the model the {@link com.bumptech.glide.load.model.ModelLoader}s built by
* this factory can handle
* @param <Y> The type of data the {@link com.bumptech.glide.load.model.ModelLoader}s built by this
* factory can load.
*/
public interface ModelLoaderFactory<T, Y> {
/**
* Build a concrete ModelLoader for this model type.
*
* @param multiFactory A map of classes to factories that can be used to construct additional
* {@link ModelLoader}s that this factory's {@link ModelLoader} may depend on
* @return A new {@link ModelLoader}
*/
@NonNull
ModelLoader<T, Y> build(@NonNull MultiModelLoaderFactory multiFactory);
/**
* A lifecycle method that will be called when this factory is about to replaced.
*/
void teardown();
}
接口比較簡(jiǎn)單，比如特殊的是還有一個(gè)工廠MultiModelLoaderFactory，其實(shí)也可以看成一種代理模式，真正去buildLoadData的是通過(guò)工廠類(lèi)StreamFactory構(gòu)造返回的urlLoader，它能處理的Model類(lèi)型是GlideUrl,返回的類(lèi)型是InputStream，而urlloader本身是通過(guò)MultiModelLoaderFactory構(gòu)造：
public ModelLoader<Uri, InputStream> build(MultiModelLoaderFactory multiFactory) {
return new UrlUriLoader<>(multiFactory.build(GlideUrl.class, InputStream.class));
}
所以我們總結(jié)下下ModelLoader,UrlUriLoader,StreamFactory,ModelLoaderFactory,MultiModelLoaderFactory的關(guān)系, 具體的ModelLoader里面有一個(gè)代理的ModelLoader,這個(gè)代理的ModelLoder由MultiModelLoaderFactory實(shí)例化，不管是外層的ModelLoader或者是代理ModelLoader都是由Factory這種方式生成，外層的ModelLoader的Factory在自己的類(lèi)名下面，而代理ModelLoader統(tǒng)一都由MultiModelLoaderFactory這個(gè)工廠生成，類(lèi)似門(mén)面模式。
StreamFactory是在Glide初始化的時(shí)候注冊(cè)到ModelLoaderRegistry中：
//Glide.java
registry.append(URL.class, InputStream.class, new UrlLoader.StreamFactory())
而ModelLoaderRegistry其實(shí)只是MultiModelLoaderFactory的外殼，它會(huì)把Glide初始化注冊(cè)的所有ModelFactory保存到MultiModelLoaderFactory:
// ModelLoaderRegistry.java
private final MultiModelLoaderFactory multiModelLoaderFactory;
private final ModelLoaderCache cache = new ModelLoaderCache();
public synchronized <Model, Data> void append(
@NonNull Class<Model> modelClass,
@NonNull Class<Data> dataClass,
@NonNull ModelLoaderFactory<? extends Model, ? extends Data> factory) {
multiModelLoaderFactory.append(modelClass, dataClass, factory);
cache.clear();
}
按照上面的邏輯，再看一個(gè)具體的ModelLoader實(shí)現(xiàn)類(lèi)FileLoader<Data> implements ModelLoader<File, Data>, 實(shí)現(xiàn)從File加載Data,這里Data有兩個(gè)類(lèi)型java.io.InputStream和java.io.FileDescriptor,看下具體實(shí)現(xiàn)。實(shí)際工作會(huì)通過(guò)內(nèi)部實(shí)例變量FileOpener完成，在FileFetcher loadData中通過(guò)FileOpener打開(kāi)文件，返回需要的數(shù)據(jù)類(lèi)型，所以關(guān)鍵就在這個(gè)FileOpener，在這里是對(duì)文件打開(kāi)關(guān)閉的一個(gè)封裝接口，根據(jù)具體的返回類(lèi)型構(gòu)造不同的FileOpener.
// FileLoader.java
public class FileLoader<Data> implements ModelLoader<File, Data> {
private static final String TAG = "FileLoader";
private final FileOpener<Data> fileOpener;
// Public API.
@SuppressWarnings("WeakerAccess")
public FileLoader(FileOpener<Data> fileOpener) {
this.fileOpener = fileOpener;
}
@Override
public LoadData<Data> buildLoadData(@NonNull File model, int width, int height,
@NonNull Options options) {
return new LoadData<>(new ObjectKey(model), new FileFetcher<>(model, fileOpener));
}
@Override
public boolean handles(@NonNull File model) {
return true;
}
/**
* Allows opening a specific type of data from a {@link java.io.File}.
* @param <Data> The type of data that can be opened.
*/
public interface FileOpener<Data> {
Data open(File file) throws FileNotFoundException;
void close(Data data) throws IOException;
Class<Data> getDataClass();
}
private static final class FileFetcher<Data> implements DataFetcher<Data> {
private final File file;
private final FileOpener<Data> opener;
private Data data;
FileFetcher(File file, FileOpener<Data> opener) {
this.file = file;
this.opener = opener;
}
@Override
public void loadData(@NonNull Priority priority, @NonNull DataCallback<? super Data> callback) {
try {
data = opener.open(file);
} catch (FileNotFoundException e) {
if (Log.isLoggable(TAG, Log.DEBUG)) {
Log.d(TAG, "Failed to open file", e);
}
callback.onLoadFailed(e);
return;
}
callback.onDataReady(data);
}
@Override
public void cleanup() {
if (data != null) {
try {
opener.close(data);
} catch (IOException e) {
// Ignored.
}
}
}
@Override
public void cancel() {
// Do nothing.
}
@NonNull
@Override
public Class<Data> getDataClass() {
return opener.getDataClass();
}
@NonNull
@Override
public DataSource getDataSource() {
return DataSource.LOCAL;
}
}
/**
* Base factory for loading data from {@link java.io.File files}.
* @param <Data> The type of data that will be loaded for a given {@link java.io.File}.
*/
public static class Factory<Data> implements ModelLoaderFactory<File, Data> {
private final FileOpener<Data> opener;
public Factory(FileOpener<Data> opener) {
this.opener = opener;
}
@NonNull
@Override
public final ModelLoader<File, Data> build(@NonNull MultiModelLoaderFactory multiFactory) {
return new FileLoader<>(opener);
}
@Override
public final void teardown() {
// Do nothing.
}
}
在FileLoader內(nèi)部有兩個(gè)靜態(tài)內(nèi)部類(lèi)StreamFactory和FileDescriptorFactory分別返回兩個(gè)數(shù)據(jù)類(lèi)型java.io.InputStream和java.io.FileDescriptor。分別構(gòu)造兩種類(lèi)型的FileOpener,一個(gè)返回InputStream類(lèi)型，另外一個(gè)返回ParcelFileDescriptor.
/**
* Factory for loading {@link InputStream}s from {@link File}s.
*/
public static class StreamFactory extends Factory<InputStream> {
public StreamFactory() {
super(new FileOpener<InputStream>() {
@Override
public InputStream open(File file) throws FileNotFoundException {
return new FileInputStream(file);
}
@Override
public void close(InputStream inputStream) throws IOException {
inputStream.close();
}
@Override
public Class<InputStream> getDataClass() {
return InputStream.class;
}
});
}
}
/**
* Factory for loading {@link ParcelFileDescriptor}s from {@link File}s.
*/
public static class FileDescriptorFactory extends Factory<ParcelFileDescriptor> {
public FileDescriptorFactory() {
super(new FileOpener<ParcelFileDescriptor>() {
@Override
public ParcelFileDescriptor open(File file) throws FileNotFoundException {
return ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY);
}
@Override
public void close(ParcelFileDescriptor parcelFileDescriptor) throws IOException {
parcelFileDescriptor.close();
}
@Override
public Class<ParcelFileDescriptor> getDataClass() {
return ParcelFileDescriptor.class;
}
});
}
}
上面兩個(gè)Factory也是Glide初始化的時(shí)候注冊(cè)到ModelLoaderRegistry中：
.append(File.class, InputStream.class, new FileLoader.StreamFactory())
.append(File.class, ParcelFileDescriptor.class, new FileLoader.FileDescriptorFactory())
2. DataFetcher
從前面ModelLoader<Model, Data>中有提到過(guò)DataFetcher<Data>這個(gè)類(lèi)，這是真正做數(shù)據(jù)拉取的功能接口，基本上對(duì)應(yīng)不同的ModelLoader會(huì)有對(duì)應(yīng)的DataFetcher去實(shí)現(xiàn)拉取數(shù)據(jù)的工作，看下DataFetcher<Data>這個(gè)類(lèi)的接口定義。里面有個(gè)內(nèi)部接口DataCallback，在數(shù)據(jù)拉取成功后會(huì)通過(guò)回調(diào)接口返回。loadData就是真正發(fā)起數(shù)據(jù)請(qǐng)求的地方，getDataSource返回?cái)?shù)據(jù)來(lái)源，這是個(gè)枚舉。
// DataSource.java
public interface DataFetcher<T> {
/**
* Callback that must be called when data has been loaded and is available, or when the load
* fails.
*
* @param <T> The type of data that will be loaded.
*/
interface DataCallback<T> {
/**
* Called with the loaded data if the load succeeded, or with {@code null} if the load failed.
*/
void onDataReady(@Nullable T data);
/**
* Called when the load fails.
*
* @param e a non-null {@link Exception} indicating why the load failed.
*/
void onLoadFailed(@NonNull Exception e);
}
void loadData(@NonNull Priority priority, @NonNull DataCallback<? super T> callback);
void cleanup();
void cancel();
/**
* Returns the class of the data this fetcher will attempt to obtain.
*/
@NonNull
Class<T> getDataClass();
/**
* Returns the {@link com.bumptech.glide.load.DataSource} this fetcher will return data from.
*/
@NonNull
DataSource getDataSource();
}
看下在Glide中DataFetcher的繼承結(jié)構(gòu)，實(shí)現(xiàn)類(lèi)還是很多，可以從AssetPath/Url/File/Uri等地方拉取數(shù)據(jù)。
看下比較常用的HttpUrlFetcher，實(shí)現(xiàn)從Url加載返回一個(gè)InputStream:
/**
* A DataFetcher that retrieves an {@link java.io.InputStream} for a Url.
*/
public class HttpUrlFetcher implements DataFetcher<InputStream>
在loadData方法中,通過(guò)loadDataWithRedirects加載url返回result,如果成功就通過(guò)onDataReady返回?cái)?shù)據(jù)：
// HttpUrlFetcher.java
InputStream result = loadDataWithRedirects(glideUrl.toURL(), 0, null, glideUrl.getHeaders());
callback.onDataReady(result);
在loadDataWithRedirects中通過(guò)HttpURLConnection發(fā)起網(wǎng)絡(luò)連接：
// HttpUrlFetcher.java
urlConnection = connectionFactory.build(url);
for (Map.Entry<String, String> headerEntry : headers.entrySet()) {
urlConnection.addRequestProperty(headerEntry.getKey(),headerEntry.getValue());
}
urlConnection.setConnectTimeout(timeout);
urlConnection.setReadTimeout(timeout);
urlConnection.setUseCaches(false);
urlConnection.setDoInput(true);
urlConnection.setInstanceFollowRedirects(false);
// Connect explicitly to avoid errors in decoders if connection fails.
urlConnection.connect();
// Set the stream so that it's closed in cleanup to avoid resource leaks. See #2352.
stream = urlConnection.getInputStream();
看下另外幾個(gè)接口方法的實(shí)現(xiàn),這里DataSource明顯就是REMOTE，返回的數(shù)據(jù)類(lèi)型是InputStream.class,在cleanup中就是把sream和connection關(guān)閉:
@Override
public void cleanup() {
if (stream != null) {
try {
stream.close();
} catch (IOException e) {
// Ignore
}
}
if (urlConnection != null) {
urlConnection.disconnect();
}
urlConnection = null;
}
@Override
public void cancel() {
isCancelled = true;
}
@NonNull
@Override
public Class<InputStream> getDataClass() {
return InputStream.class;
}
@NonNull
@Override
public DataSource getDataSource() {
return DataSource.REMOTE;
}
3.總結(jié)
再回頭看前面提的問(wèn)題，Glide提供很多ModelLoader接口的實(shí)現(xiàn)類(lèi)來(lái)實(shí)現(xiàn)不同資源的數(shù)據(jù)加載，每個(gè)ModelLoader不是直接通過(guò)構(gòu)造函數(shù)實(shí)例化，而是每個(gè)Loader內(nèi)部提供的工廠類(lèi)進(jìn)行實(shí)例化，在Glide初始化的時(shí)候，會(huì)把這些工廠類(lèi)都注冊(cè)到ModelLoaderRegistry中，構(gòu)造的時(shí)候從里面取出對(duì)應(yīng)的工廠實(shí)例化ModelLoader。ModelLoader下載數(shù)據(jù)會(huì)通過(guò)DataFetcher，DataFetcher的實(shí)現(xiàn)類(lèi)基本和ModelLoader對(duì)應(yīng)。
