gradle:
compile 'com.squareup.picasso:picasso:2.5.2'
使用:
Picasso.with(this).load("http://...../photo3.jpg").into(myImg);
自定义的使用方法:
Picasso picasso = new Picasso.Builder(this)
.memoryCache(new LruCache()) // 设置自定义的内存缓存
.addRequestHandler(requestHandler) // 设置自定义的RequestHandler
.defaultBitmapConfig(bitmapConfig) // 设置自定义的Bitmap Config
.downloader(okHttpDownloader) // 设置自定义的Downloader
.executor(executorService) // 设置自定义的线程池
.requestTransformer(transformer) // 设置自定义的Transformor
.listener(listener) // 添加Listener进行监听
.build();
picasso.load(File/resId/Uri/String)
.resize(width, height)
.centerInside()
.into(imageView);
public static Picasso with(Context context) {
if (singleton == null) {
synchronized (Picasso.class) {
if (singleton == null) {
singleton = new Builder(context).build();
}
}
}
return singleton;
}
简单的多线程单例模式;同时使用Buidler模式来创建Picasso实例。
/** Start building a new {@link Picasso} instance. */
public Builder(Context context) {
if (context == null) {
throw new IllegalArgumentException("Context must not be null.");
}
this.context = context.getApplicationContext();
}
private Downloader downloader;
private ExecutorService service;
private Cache cache;
private Listener listener;
private RequestTransformer transformer;
private List requestHandlers;
private Bitmap.Config defaultBitmapConfig;
/** Create the {@link Picasso} instance. */
public Picasso build() {
Context context = this.context;
// 为这一系列变量进行默认初始化
// Downloader执行实际的下载业务,返回Response
if (downloader == null) {
downloader = Utils.createDefaultDownloader(context);
}
// 内存缓存,可以看到默认的是LruCache
if (cache == null) {
cache = new LruCache(context);
}
// 线程池,执行网络请求的地方
if (service == null) {
service = new PicassoExecutorService();
}
// request发送前进行处理
if (transformer == null) {
transformer = RequestTransformer.IDENTITY;
}
// 用以统计
Stats stats = new Stats(cache);
// 进行Request以及Response的转发
Dispatcher dispatcher = new Dispatcher(context, service, HANDLER, downloader, cache, stats);
// 创建一个Picasso
return new Picasso(context, dispatcher, cache, listener, transformer, requestHandlers, stats,
defaultBitmapConfig, indicatorsEnabled, loggingEnabled);
}
可以看到这里为许多重要类进行了默认初始化,后面获取图片使用到的都是这些默认的变量,当然这些变量也都可以进行自定义;
Downloader:默认实现是OkHttpDownloader,Picasso是对OkHttp的封装,它的网络请求以及对本地Cache的请求都是直接通过OkHttp来实现的;Downloader是实现本地磁盘查询,以及发起网络请求的类;
Cache:内存缓存;这里采用的LruCache,也可以自行定义。缓存的是进行网络请求后,大小等裁剪之后的图片资源。
PicassoExecutorService: Picasso之中的线程池,默认核心线程为3个,没有非核心线程;但也会根据手机当前的网络状态进行适时改变,比如WIFI状态的核心线程就为4个,而4G,3G,2G状态下的线程数分别为3,2,1个;
Stats:进行一些数据统计,比如图片下载命中率等。
RequestTransformer:用来预处理Request,必须修改域名等
Dispatcher:用以分发任务,它通过启动了一个DispatcherThread线程,然后创建一个用来处理消息的DispatcherHandler,该Handler的数据处理是在DispatcherThread中进行的。
RequestHandler: 后面将会看到,该对象用来持有一个具体的Request,所有Request最终其实都是由其对应的RequestHandler来进行处理的。
根据后面具体使用情况再做分析:
public RequestCreator load(String path) {
if (path == null) {
return new RequestCreator(this, null, 0);
}
if (path.trim().length() == 0) {
throw new IllegalArgumentException("Path must not be empty.");
}
return load(Uri.parse(path));
}
public RequestCreator load(Uri uri) {
return new RequestCreator(this, uri, 0);
}
这里创建一个RequestCreator
private final Picasso picasso;
private final Request.Builder data;
RequestCreator(Picasso picasso, Uri uri, int resourceId) {
if (picasso.shutdown) {
throw new IllegalStateException(
"Picasso instance already shut down. Cannot submit new requests.");
}
this.picasso = picasso;
this.data = new Request.Builder(uri, resourceId, picasso.defaultBitmapConfig);
}
data对应创建一个Request的Builder,这个Request中封装了了相应的请求信息,传入了请求加载图片的URI,已经resourceId,以及默认显示图片的配置信息。
进而一般调用into将图片加载到相应的控件中。
// RequestCreator.java
public void into(ImageView target) {
into(target, null);
}
public void into(ImageView target, Callback callback) {
long started = System.nanoTime();
// 盘算是否是在主线程,如果不是则会抛出异常
checkMain();
if (target == null) {
throw new IllegalArgumentException("Target must not be null.");
}
// 判断reqeust是否合法,即存在URI或者对应的resId,否则会取消该请求
if (!data.hasImage()) {
picasso.cancelRequest(target);
if (setPlaceholder) {
setPlaceholder(target, getPlaceholderDrawable());
}
return;
}
// 判断是否需要延期执行
if (deferred) {
// 判断是否已经设置了宽高大小
if (data.hasSize()) {
throw new IllegalStateException("Fit cannot be used with resize.");
}
// 获取目标控件的宽高参数
int width = target.getWidth();
int height = target.getHeight();
// 表示当前控件并未加载到界面上(宽或高为0)
if (width == 0 || height == 0) {
if (setPlaceholder) {
setPlaceholder(target, getPlaceholderDrawable());
}
// 生成DeferredRequestCreator,加入相应队列进行处理
picasso.defer(target, new DeferredRequestCreator(this, target, callback));
return;
}
// 设置Request.Builder中的宽高参数大小
data.resize(width, height);
}
// 创建Request
Request request = createRequest(started);
// 获取request对应的key
String requestKey = createKey(request);
// 根据策略判断是够需要跳过读取MemoryCache
if (shouldReadFromMemoryCache(memoryPolicy)) { // 尝试从MemoryCache中获取Bitmap
// 根据Requeskey来获取相应的Bitmap
Bitmap bitmap = picasso.quickMemoryCacheCheck(requestKey);
if (bitmap != null) {
// 如果从MemoryCache中获取到相应的bitmap,则取消request
picasso.cancelRequest(target);
// 设置图片
setBitmap(target, picasso.context, bitmap, MEMORY, noFade, picasso.indicatorsEnabled);
if (picasso.loggingEnabled) {
log(OWNER_MAIN, VERB_COMPLETED, request.plainId(), "from " + MEMORY);
}
// 调用回调callback的onSuccess函数
if (callback != null) {
callback.onSuccess();
}
return;
}
}
// 如果从MemoryCache获取图片失败,或者根据缓存策略直接跳过读取MemoryCache,则设置默认图片
if (setPlaceholder) {
setPlaceholder(target, getPlaceholderDrawable());
}
// 创建ImageViewAction,Action里面包含了一次请求所需要的所有信息
Action action =
new ImageViewAction(picasso, target, request, memoryPolicy, networkPolicy, errorResId,
errorDrawable, requestKey, tag, callback, noFade);
// 将action入队列
picasso.enqueueAndSubmit(action);
}
整个图片加载流程和一般的三级缓存加载流程相似,下图已经介绍地很清晰:
上面主要是尝试从MemoryCache中获取对应Bitmap,如果获取失败,再创建Action,通过将Action入队列,然后从本地Cache以及网络上去获取该图片。
接着上面enqueueAndSubmit继续分析
// Picasso.java
final Map
targetToAction是一个Map,它存储的是Target对应的Action,以Target为相应key值。
当新添加一个action时,首先尝试取消该Action对应的Target之前的Action请求,然后将新Action添加到Map中;
然后提交action请求;
先来看下取消一个Request的函数cancelExistingReqeust,常用的cancelReqeust也是直接调用该函数实现的:
// Picasso.java
final Map
简单的cancel逻辑:
这里依然也需要先判断事件处理是否是在主线程中进行的;
然后尝试从targetToAction中删除该Target中对应的Action,如果该Action确实存在,则调用cancel函数取消该Action,并且调用Dispatcher来分发该cancel请求;
对应ImageView类型的target,前面分析中提到当需要defer即延迟的请求时,是通过创建DeferredReqeustCreator,并添加到一个Map中来实现的,这里同理应将其删除并cancel掉;
再来看看其cancel函数:
// ImageViewAction.java
class ImageViewAction extends Action {
Callback callback;
@Override void cancel() {
super.cancel();
if (callback != null) {
callback = null;
}
}
}
// Action.java
abstract class Action {
boolean cancelled;
void cancel() {
cancelled = true;
}
}
和Volley这些差不多,通过设置一个cancel标志来实现。
// Dispatcher.java
void dispatchCancel(Action action) {
handler.sendMessage(handler.obtainMessage(REQUEST_CANCEL, action));
}
分发逻辑较为简单,使用Handler来实现的;
这里来具体来看下Dispatcher的定义,来确定handler的定义;Dispathcer是在创建Picasso时默认创建了一个Dispathcer实例,如下所示:
// Picasso.java
Dispatcher dispatcher = new Dispatcher(context, service, HANDLER, downloader, cache, stats);
static final Handler HANDLER = new Handler(Looper.getMainLooper()) {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
...
}
}
}
而Dispatcher中的Handler并不是这个Handler,而是又做了一个封装:
this.handler = new DispatcherHandler(dispatcherThread.getLooper(), this);
// Dispatcher.java
private static class DispatcherHandler extends Handler {
private final Dispatcher dispatcher;
public DispatcherHandler(Looper looper, Dispatcher dispatcher) {
super(looper);
this.dispatcher = dispatcher;
}
@Override public void handleMessage(final Message msg) {
switch (msg.what) {
case REQUEST_SUBMIT: {
Action action = (Action) msg.obj;
dispatcher.performSubmit(action);
break;
}
case REQUEST_CANCEL: {
Action action = (Action) msg.obj;
dispatcher.performCancel(action);
break;
}
.......
default:
Picasso.HANDLER.post(new Runnable() {
@Override public void run() {
throw new AssertionError("Unknown handler message received: " + msg.what);
}
});
}
}
}
Dispathcer的作用是通过handler将相应的操作逻辑转换到自己Looper对应线程中去实现,然后调用performCancel去具体处理该Action;
下面接着来看Dispatcher#performCancel:
// Dispatcher.java
final Map hunterMap;
final Set
逻辑较为简单,主要从各个可能存储该Action的集合中将其删除,如果已经有Bitmap在执行,则调用去cancel去处理。里面引出一个重要的类BitmapHunter,下面将会进行介绍。
如果没有从MemoryCache中获取到Bitmap(分两种情况,一直是根据policy直接跳过从MemoryCache中获取;另一种是MemoryCache中并没有对应的Bitmap缓存),这是将会来到submit(Action);
// Picasso.java
void submit(Action action) {
dispatcher.dispatchSubmit(action);
}
和前面类似。继续调用Dispatcher来分发submit事件,因此可以看出Dispatcher的主要作用是对Picasso(主线程)中发送的事件进行分发处理;
和dispatchCancel类似,接下来会来到performSubmit:
final Set pausedTags;
final Map failedActions;
final Map pausedActions;
final Map hunterMap;
final ExecutorService service;
void performSubmit(Action action, boolean dismissFailed) {
// 如果Action已经暂停
if (pausedTags.contains(action.getTag())) {
pausedActions.put(action.getTarget(), action);
return;
}
// 获取对应的BitmapHunter
BitmapHunter hunter = hunterMap.get(action.getKey());
if (hunter != null) { // 如果对应hunter不为null,表示前面有同样的请求在进行,因此这是可以合并请求
hunter.attach(action);
return;
}
// 判断是否已经关闭
if (service.isShutdown()) {
return;
}
// 创建BitmapHunter
hunter = forRequest(action.getPicasso(), this, cache, stats, action);
// 将Bitmap提交到线程池
hunter.future = service.submit(hunter);
// 保存Bitmap
hunterMap.put(action.getKey(), hunter);
if (dismissFailed) {
failedActions.remove(action.getTarget());
}
}
具体的工作逻辑如下图:
当遇到相同的Action时,Picasso会通过BitmapHunter的Attach来合并相同的请求,避免同一个请求重复进行;简单看下attach:
// BitmapHunter.java
void attach(Action action) {
boolean loggingEnabled = picasso.loggingEnabled;
Request request = action.request;
// 如果BitmapHunter对应的action仍未设置,则直接设置action返回
if (this.action == null) {
this.action = action;
return;
}
// 创建一个保存相同Action的ArrayList
if (actions == null) {
actions = new ArrayList(3);
}
actions.add(action);
// 获得Action的优先级
Picasso.Priority actionPriority = action.getPriority();
// 如果新添加Action的Priority优先级高于原来的优先级,则更新该Bitmaphunter的优先级
if (actionPriority.ordinal() > priority.ordinal()) {
priority = actionPriority;
}
}
可以看到合并相同请求,则是在BitmapHunter中维护一个Action列表actions;
当新添加Action的Priority优先级高于原来的优先级,则更新该BitmapHunter的优先级大小;
这里在来关注下Picasso中的优先级问题:
/**
* The priority of a request.
*
* @see RequestCreator#priority(Priority)
*/
public enum Priority {
LOW,
NORMAL,
HIGH
}
Picasso中Priority是个枚举类,总共分为LOW,NORMAL,HIGH三个等级;而相对应地,Volley中Request的Priority则多了一个IMMEDIATE等级;顺便提下Volley中Reqeust可以根据Priority进行执行的原因是因为其实现了Comparable接口:
Volley#Reqeust:
public abstract class Request<T> implements Comparable<Request<T>> {
public enum Priority {
LOW,
NORMAL,
HIGH,
IMMEDIATE
}
@Override
public int compareTo(Request other) {
Priority left = this.getPriority();
Priority right = other.getPriority();
// High-priority requests are "lesser" so they are sorted to the front.
// Equal priorities are sorted by sequence number to provide FIFO ordering.
return left == right ?
this.mSequence - other.mSequence :
right.ordinal() - left.ordinal();
}
}
再来看下线程池ExecutorService,它是在Picasso创建之初Builder时就创建的,默认的实现为:
// Picasso.Builder
private ExecutorService service;
if (service == null) {
service = new PicassoExecutorService();
}
// PicassoExecutorService
class PicassoExecutorService extends ThreadPoolExecutor {
// 默认的线程池的线程数量
private static final int DEFAULT_THREAD_COUNT = 3;
PicassoExecutorService() {
super(DEFAULT_THREAD_COUNT, DEFAULT_THREAD_COUNT, 0, TimeUnit.MILLISECONDS,
new PriorityBlockingQueue(), new Utils.PicassoThreadFactory());
}
}
Picasso提供的是个默认核心线程数为3个,没有非核心线程(最大的线程数目也是为3),任务队列为PriorityBlockingQueue的线程池;
Picasso有个有趣的地方是,它可以根据当前应用的网络状态实时调整线程池中的线程数目:
// 根据网络状况调整线程池中线程的数量
void adjustThreadCount(NetworkInfo info) {
if (info == null || !info.isConnectedOrConnecting()) {
setThreadCount(DEFAULT_THREAD_COUNT);
return;
}
switch (info.getType()) {
case ConnectivityManager.TYPE_WIFI:
case ConnectivityManager.TYPE_WIMAX:
case ConnectivityManager.TYPE_ETHERNET:
setThreadCount(4);
break;
case ConnectivityManager.TYPE_MOBILE:
switch (info.getSubtype()) {
case TelephonyManager.NETWORK_TYPE_LTE: // 4G
case TelephonyManager.NETWORK_TYPE_HSPAP:
case TelephonyManager.NETWORK_TYPE_EHRPD:
setThreadCount(3);
break;
case TelephonyManager.NETWORK_TYPE_UMTS: // 3G
case TelephonyManager.NETWORK_TYPE_CDMA:
case TelephonyManager.NETWORK_TYPE_EVDO_0:
case TelephonyManager.NETWORK_TYPE_EVDO_A:
case TelephonyManager.NETWORK_TYPE_EVDO_B:
setThreadCount(2);
break;
case TelephonyManager.NETWORK_TYPE_GPRS: // 2G
case TelephonyManager.NETWORK_TYPE_EDGE:
setThreadCount(1);
break;
default:
setThreadCount(DEFAULT_THREAD_COUNT);
}
break;
default:
setThreadCount(DEFAULT_THREAD_COUNT);
}
}
// 线程线程数量
private void setThreadCount(int threadCount) {
setCorePoolSize(threadCount);
setMaximumPoolSize(threadCount);
}
即WIFI状态下线程数目为4,4G状态下为3,3G状态下为2,2G转态下线程池中只有一个线程;
再来看线程池中创建线程的Factory,看看Picasso的线程池中的线程有何特别之处:
static class PicassoThreadFactory implements ThreadFactory {
@SuppressWarnings("NullableProblems")
public Thread newThread(Runnable r) {
return new PicassoThread(r);
}
}
private static class PicassoThread extends Thread {
public PicassoThread(Runnable r) {
super(r);
}
@Override public void run() {
Process.setThreadPriority(THREAD_PRIORITY_BACKGROUND);
super.run();
}
}
PicassoThread简单的Thread,线程优先级为后台线程;
再看service提交submit一个BitmapHunter时的操作逻辑:
// PicassoExecutorService
class PicassoExecutorService extends ThreadPoolExecutor {
// 提交任务
@Override
public Future submit(Runnable task) {
PicassoFutureTask ftask = new PicassoFutureTask((BitmapHunter) task);
execute(ftask);
return ftask;
}
// 将BitmapHunter封装成PicassoFutureTask进行execute
private static final class PicassoFutureTask extends FutureTask<BitmapHunter>
implements Comparable<PicassoFutureTask> {
private final BitmapHunter hunter;
public PicassoFutureTask(BitmapHunter hunter) {
super(hunter, null);
this.hunter = hunter;
}
@Override
public int compareTo(PicassoFutureTask other) {
Picasso.Priority p1 = hunter.getPriority();
Picasso.Priority p2 = other.hunter.getPriority();
// High-priority requests are "lesser" so they are sorted to the front.
// Equal priorities are sorted by sequence number to provide FIFO ordering.
return (p1 == p2 ? hunter.sequence - other.hunter.sequence : p2.ordinal() - p1.ordinal());
}
}
}
可以看到在submit中将BitmapHunter封装成一个FutureTask进行execute;
PicassoFutureTask可以实现对当前Runnbale运行结果的查看及控制;同期它提供了和Volley一个样的Priority一样的优先级机制。
回到前面performSubmit的执行逻辑,接下来会创建以及执行BitmapHunter,下面重点介绍BitmapHunter,它是一个任务具体执行的整体:
// BitmapHunter.java
static BitmapHunter forRequest(Picasso picasso, Dispatcher dispatcher, Cache cache, Stats stats,
Action action) {
// 根据Action获取对应Request
Request request = action.getRequest();
// 获取requestHandlers
List requestHandlers = picasso.getRequestHandlers();
// Index-based loop to avoid allocating an iterator.
//noinspection ForLoopReplaceableByForEach
// 查找使用能够处理该Request的requesthandler,如果有则传入BitmapHandler
for (int i = 0, count = requestHandlers.size(); i < count; i++) {
RequestHandler requestHandler = requestHandlers.get(i);
if (requestHandler.canHandleRequest(request)) {
return new BitmapHunter(picasso, dispatcher, cache, stats, action, requestHandler);
}
}
// 使用默认的ERRORING_HANDLER来构造BitmapHunter
return new BitmapHunter(picasso, dispatcher, cache, stats, action, ERRORING_HANDLER);
}
先判断Picasso中是否已经设置了能够处理该Request的requestHandler,如果存在则传入BitmapHandler,如果不存在,则使用默认的ERRORING_HANDLER来构造BitmapHandler;
简单看下ERRORING_HANDLER:
// BitmapHunter.java
private static final RequestHandler ERRORING_HANDLER = new RequestHandler() {
@Override public boolean canHandleRequest(Request data) {
return true;
}
@Override public Result load(Request request, int networkPolicy) throws IOException {
throw new IllegalStateException("Unrecognized type of request: " + request);
}
};
事实上处理Request请求主要是通过reqeustHandler的load函数来进行处理的,然后将处理后的结果封装成Result,然后返回;Picasso在其构造函数中提供了一些列的RequestHandler:
List allRequestHandlers =
new ArrayList(builtInHandlers + extraCount);
// ResourceRequestHandler needs to be the first in the list to avoid
// forcing other RequestHandlers to perform null checks on request.uri
// to cover the (request.resourceId != 0) case.
allRequestHandlers.add(new ResourceRequestHandler(context));
if (extraRequestHandlers != null) {
allRequestHandlers.addAll(extraRequestHandlers);
}
allRequestHandlers.add(new ContactsPhotoRequestHandler(context));
allRequestHandlers.add(new MediaStoreRequestHandler(context));
allRequestHandlers.add(new ContentStreamRequestHandler(context));
allRequestHandlers.add(new AssetRequestHandler(context));
allRequestHandlers.add(new FileRequestHandler(context));
allRequestHandlers.add(new NetworkRequestHandler(dispatcher.downloader, stats));
requestHandlers = Collections.unmodifiableList(allRequestHandlers);
可以看到,按照不同的Request,Picasso提供了不同的RequestHandler进行处理,比如从资源中进行加载的则使用ResourceRequestHandler,从文件中加载则调用FileRequestHandler,从网络中直接下载使用NetworkRequestHandler等等。
下面将会看到这些RequestHandler的具体处理作用;
// BitmapHunter.java
class BitmapHunter implements Runnable {
/**
* Global lock for bitmap decoding to ensure that we are only are decoding one at a time. Since
* this will only ever happen in background threads we help avoid excessive memory thrashing as
* well as potential OOMs. Shamelessly stolen from Volley.
*/
private static final Object DECODE_LOCK = new Object();
@Override
public void run() {
try {
updateThreadName(data);
// 主要的执行逻辑在hunt方法中
result = hunt();
// 通过Dispatcher来分发运行之后的结果
if (result == null) {
dispatcher.dispatchFailed(this);
} else {
dispatcher.dispatchComplete(this);
}
// 下面是进行运行过程中的一邪猎以往情况的处理
} catch (Downloader.ResponseException e) {
if (!e.localCacheOnly || e.responseCode != 504) {
exception = e;
}
dispatcher.dispatchFailed(this);
} catch (NetworkRequestHandler.ContentLengthException e) {
exception = e;
dispatcher.dispatchRetry(this);
} catch (IOException e) {
exception = e;
dispatcher.dispatchRetry(this);
} catch (OutOfMemoryError e) {
StringWriter writer = new StringWriter();
stats.createSnapshot().dump(new PrintWriter(writer));
exception = new RuntimeException(writer.toString(), e);
dispatcher.dispatchFailed(this);
} catch (Exception e) {
exception = e;
dispatcher.dispatchFailed(this);
} finally {
Thread.currentThread().setName(Utils.THREAD_IDLE_NAME);
}
}
}
BitmapHunter实际上是一个Runnable,重点看其run中的执行逻辑;看到执行较为简单,都是通过hunt这个函数来实现的,获取到结果后,根据结果的成功与否,通过Dispatcher进行转发结果;
BitmapHunter中有一个成员变量较为有趣,DECODE_LOCK,这个变量在Volley中出现过,而且代码作者也说这是它从Volley中学习过来来,从名称中就可以看出,它是用来在解码图片时使用的锁,用来保证系统在同一时刻只有一个线程在解码图片;
// BitmapHunter.java
final Request data;
Bitmap hunt() throws IOException {
Bitmap bitmap = null;
// 这里还是先尝试从MemoryCache中去获取Bitmap
if (shouldReadFromMemoryCache(memoryPolicy)) {
bitmap = cache.get(key);
if (bitmap != null) { // 如果获取成功,直接返回
stats.dispatchCacheHit(); // 统计命中信息
loadedFrom = MEMORY; // loadedFrom记录表示从Memory缓存中获取
return bitmap;
}
}
data.networkPolicy = retryCount == 0 ? NetworkPolicy.OFFLINE.index : networkPolicy;
// 通过RequestHandler.load来处理Request获取结果
RequestHandler.Result result = requestHandler.load(data, networkPolicy);
// 如果处理结果成功
if (result != null) {
loadedFrom = result.getLoadedFrom();
exifRotation = result.getExifOrientation();
// 从结果中获取Bitmap
bitmap = result.getBitmap();
// If there was no Bitmap then we need to decode it from the stream.
// 如果Bitmap为null,则需要将Stream转化成Bitmap
if (bitmap == null) {
InputStream is = result.getStream();
try {
bitmap = decodeStream(is, data); // 将网络数据流decode成Bitmap
} finally {
Utils.closeQuietly(is);
}
}
}
if (bitmap != null) {
// 更新统计信息
stats.dispatchBitmapDecoded(bitmap);
// 判断是否需要进行Transformation,即进行转换
if (data.needsTransformation() || exifRotation != 0) {
// 这里体现了前面提到的DECODE_LOCK的作用,它保证在同一时刻,只有一个线程在执行图形变换
synchronized (DECODE_LOCK) {
if (data.needsMatrixTransform() || exifRotation != 0) {
bitmap = transformResult(data, bitmap, exifRotation);
}
if (data.hasCustomTransformations()) {
bitmap = applyCustomTransformations(data.transformations, bitmap);
}
}
if (bitmap != null) {
stats.dispatchBitmapTransformed(bitmap);
}
}
}
return bitmap;
}
hunt获取Bitmap的流程也较为清晰,首先仍然进行一次尝试从MemoryCache中进行获取;
获取失败,通过requestHandler的load函数进行加载,加载返回的结果为Result;
然后判断获取到的结果是否已经是Bitmap,如果不是,则需要将其从Stream转化成Bitmap;
然后判断是否需要Transformation;使用Transformation可以实现对获取到的图片的转化,一般的使用方式为:
Picasso.with(this).load("").transform(new Transformation() {
@Override
public Bitmap transform(Bitmap source) {
// 进行图片转换
return null;
}
@Override
public String key() {
return null;
}
}).into(mImageView);
使用transform方法中添加Transformation进行图片处理,相应的图片处理开源库picasso-transformations源码地址已经集成了一些常用的Transformation可以直接进行使用;
transform的主要作用是将新创建Transformation对象添加到Request的transformations这个ArrayList中;
因而判断Request是否需要进行transform的方法:
// Request.java
boolean needsTransformation() {
return needsMatrixTransform() || hasCustomTransformations();
}
// 判断是否需要矩阵变换
boolean needsMatrixTransform() {
return hasSize() || rotationDegrees != 0;
}
// 即将Bitmap转化成ImageView适合的尺寸
public boolean hasSize() {
return targetWidth != 0 || targetHeight != 0;
}
// 判断用户是否添加了相应的Transformation
boolean hasCustomTransformations() {
return transformations != null;
}
然后根据需要,对图片进行转换;
这里转换时使用到了前面所提到的DECODE_LOCK,它保证在同一时刻,只有一个线程在执行图形变换操作;
流程梳理清楚了,下面接着来看通过requestHandler接着获取Bitmap的过程,这里通过NetworkRequestHandler为例,即从网络中获取;
// NetWorkRequestHandler.java
class NetworkRequestHandler extends RequestHandler {
private final Downloader downloader;
@Override
public RequestHandler.Result load(Request request, int networkPolicy) throws IOException {
// 可以看到真正处理网络请求的操作时通过downloader来实现的
Downloader.Response response = downloader.load(request.uri, request.networkPolicy);
// 下面处理response结果
if (response == null) {
return null;
}
// 判断数据是从磁盘还是网络总获取的
Picasso.LoadedFrom loadedFrom = response.cached ? DISK : NETWORK;
Bitmap bitmap = response.getBitmap();
if (bitmap != null) { // 如果可以直接获取到Bitmap,则将其封装成Result,返回
return new RequestHandler.Result(bitmap, loadedFrom);
}
// 否则获取其输入流InputStream
InputStream is = response.getInputStream();
if (is == null) {
return null;
}
// Sometimes response content length is zero when requests are being replayed. Haven't found
// root cause to this but retrying the request seems safe to do so.
// 处理无效的Content长度为0的情况
if (loadedFrom == DISK && response.getContentLength() == 0) {
Utils.closeQuietly(is);
// 抛出ContentLengthException,在Bitmap的run函数中会处理该异常,会调用retry进行重试
throw new ContentLengthException("Received response with 0 content-length header.");
}
if (loadedFrom == NETWORK && response.getContentLength() > 0) {
stats.dispatchDownloadFinished(response.getContentLength());
}
// 封装成Result,返回
return new RequestHandler.Result(is, loadedFrom);
}
}
这里可以看到,真正处理请求的其实是Downloader这个实例,处理后返回的结果为Response;
Response中返回的结果可能有两种情况,一种是可能已经获取到了bitmap,一种可能是InputStream,这里需要分别进行处理,封装成Result,返回给BitmapHunter;
这里有个细节,当从磁盘中获取的结果Content的长度为0时,这里会抛出ContentLengthException异常,在BitmapHunter的run函数中会处理该异常,会调用retry进行重试;
downloader也是在Picasso初始化时就创建了的,如下所示:
if (downloader == null) {
downloader = Utils.createDefaultDownloader(context);
}
// Utils.java
static Downloader createDefaultDownloader(Context context) {
try {
Class.forName("com.squareup.okhttp.OkHttpClient");
return OkHttpLoaderCreator.create(context);
} catch (ClassNotFoundException ignored) {
}
return new UrlConnectionDownloader(context);
}
可以看到这里提供了两种实现,一种是如果系统中已经添加了OkhttpClient依赖,则使用Class.forName加载OkHttpClient类时,会加载成功,这时使用OkHttpLoaderCreator进行创建,也就是下面的网络请求通过okHttp来实现;否则是使用Android中默认提供的UrlConnection;这里一句OkHttp来进行分析;
// Utils.java
private static class OkHttpLoaderCreator {
static Downloader create(Context context) {
return new OkHttpDownloader(context);
}
}
则Downloader的真是类型为OkHttpDownloader;
先来看下OkHttpDownloader的一些具体细节:
// Utils.java
// 创建Cache的文件地址
private static final String PICASSO_CACHE = "picasso-cache";
static File createDefaultCacheDir(Context context) {
File cache = new File(context.getApplicationContext().getCacheDir(), PICASSO_CACHE);
if (!cache.exists()) {
//noinspection ResultOfMethodCallIgnored
cache.mkdirs();
}
return cache;
}
// OkHttpDownloader.java
public class OkHttpDownloader implements Downloader {
private static OkHttpClient defaultOkHttpClient() {
OkHttpClient client = new OkHttpClient();
// 设置OkHttpClient中的一些参数
client.setConnectTimeout(Utils.DEFAULT_CONNECT_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
client.setReadTimeout(Utils.DEFAULT_READ_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
client.setWriteTimeout(Utils.DEFAULT_WRITE_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
return client;
}
private final OkHttpClient client;
/**
* Create new downloader that uses OkHttp. This will install an image cache into your application
* cache directory.
*/
// 一系列构造函数
// 构造函数的主要作用其实只是为了创建OkHttpClient
public OkHttpDownloader(final Context context) {
this(Utils.createDefaultCacheDir(context));
}
public OkHttpDownloader(final File cacheDir) {
this(cacheDir, Utils.calculateDiskCacheSize(cacheDir));
}
public OkHttpDownloader(final File cacheDir, final long maxSize) {
this(defaultOkHttpClient());
try {
// 设置Cache地址,使用的是OkHttp中的Cache
client.setCache(new com.squareup.okhttp.Cache(cacheDir, maxSize));
} catch (IOException ignored) {
}
}
public OkHttpDownloader(OkHttpClient client) {
this.client = client;
}
}
这里提供了一系列OkHttpDownloader的构造函数及创建细节,其实最主要的工作只是为了创建OkHttpClient;
具体来看其load执行网络请求的细节:
// OkHttpDownloader.java
@Override
public Downloader.Response load(Uri uri, int networkPolicy) throws IOException {
CacheControl cacheControl = null;
// 构建Cache的相关执行策略
if (networkPolicy != 0) {
if (NetworkPolicy.isOfflineOnly(networkPolicy)) { // 如果要求强制从网络中获取
cacheControl = CacheControl.FORCE_CACHE;
} else {
CacheControl.Builder builder = new CacheControl.Builder();
if (!NetworkPolicy.shouldReadFromDiskCache(networkPolicy)) { // 判断是否允许读取Disk缓存
builder.noCache(); // DiskCache不允许读
}
if (!NetworkPolicy.shouldWriteToDiskCache(networkPolicy)) { // 判断是否允许写入Disk缓存
builder.noStore(); // DiskCache不允许写
}
cacheControl = builder.build();
}
}
// 根据URI创建OkHttp中的Request
com.squareup.okhttp.Request.Builder builder = new com.squareup.okhttp.Request.Builder().url(uri.toString());
if (cacheControl != null) {
builder.cacheControl(cacheControl);
}
// 典型的okHttp的同步执行方式来获取网络请求
com.squareup.okhttp.Response response = client.newCall(builder.build()).execute();
int responseCode = response.code();
// 处理失败的请求
if (responseCode >= 300) {
response.body().close();
throw new Downloader.ResponseException(responseCode + " " + response.message(), networkPolicy,
responseCode);
}
boolean fromCache = response.cacheResponse() != null;
ResponseBody responseBody = response.body();
// 将获取到的结果封装成Response返回给RequestHandler
return new Downloader.Response(responseBody.byteStream(), fromCache, responseBody.contentLength());
}
请求过程完全交由OkHttp来实现的,过程较为简单,不再赘述;这里有个细节问题,这里使用的OkHttp中的同步执行方式,因为这里执行load的线程就已经是非主线程了,故选择同步执行方式即可;具体的从DISK以及Network中来获取Response的工作完全交给OkHttp进行执行即可;
至此获取Bitmap的工作已经完成,主要的所有逻辑可以总结为
1)首先创建一个Request,Request中包含了一个请求中的相关信息,这是尝试从MemoryCache中获取,如果获取成功则直接返回,否则将Request封装成Action,然后enqueueAndSubmit;
2)在submit中,如果有相同的Action请求,则合并后来的Action请求,同一个actions集合,只需要执行一个Action就可以获取到结果;
如果之前并没有相同的Action请求,则使用Action创建一个Runnable即重要的BitmapHunter,通过线程池ExecutorService来submit执行;
3)BitmapHunter的主要执行逻辑在run函数中;而获取Bitmap的操作主要通过hunt函数来获取;hunt接着调用Request相对应的适合处理该request的RequestHandler的load函数进行处理,比如处理网络请求则需要使用NetworkRequestHandler;
4)RequestHandler的load函数其实也只是一层封装,真正执行网络请求的是Downloader这个类,对应于实际情况就是OkHttpDownloader;它的所有网络请求也都是直接交由OkHttp来完成的,因此Picasso和Retrofit一样都可以看做是对OkHttp的进一步封装;
获取Bitmap成功后,回来BitmapHunter的run方法继续来看对于结果是怎么处理的:
// 通过Dispatcher来分发运行之后的结果
if (result == null) {
dispatcher.dispatchFailed(this);
} else {
dispatcher.dispatchComplete(this);
}
// Dispatcher
void dispatchComplete(BitmapHunter hunter) {
handler.sendMessage(handler.obtainMessage(HUNTER_COMPLETE, hunter));
}
private static class DispatcherHandler extends Handler {
@Override public void handleMessage(final Message msg) {
switch (msg.what) {
case HUNTER_COMPLETE: {
BitmapHunter hunter = (BitmapHunter) msg.obj;
dispatcher.performComplete(hunter);
break;
}
}
}
}
void performComplete(BitmapHunter hunter) {
// 判断是否允许写入到MemoryCache中
if (shouldWriteToMemoryCache(hunter.getMemoryPolicy())) {
cache.set(hunter.getKey(), hunter.getResult());
}
// 从hunterMap中移除该BitmapHunter
hunterMap.remove(hunter.getKey());
batch(hunter);
}
final List batch;
private static final int BATCH_DELAY = 200; // ms
private void batch(BitmapHunter hunter) {
// 如果hunter取消了,则直接返回
if (hunter.isCancelled()) {
return;
}
// 进行打包发送
batch.add(hunter);
if (!handler.hasMessages(HUNTER_DELAY_NEXT_BATCH)) {
handler.sendEmptyMessageDelayed(HUNTER_DELAY_NEXT_BATCH, BATCH_DELAY);
}
}
Dispatcher即进行一些结果上的转发以及线程间的转换,都是同handler来实现的;前面提到这里handler对应的是DispatcherHandler,对应的Dispatcher所在的线程,然后使用该handler分发结果;
首先判断系统是否允许将获取到的结果写入到memoryCache中;然后执行完成过一个BitmapHunter之后,注意将其从hunterMap中移除;Picasso中分发结果是采用batch打包分发的,它每200ms分发一次,通过的就是batch函数中实现的;
handler发送一个延迟时间为200ms的类型为 HUNTER_DELAY_NEXT_BATCH的Message,在这200ms之内,下面将要转发的hunter事件,因为handler.hasMessages(HUNTER_DELAY_NEXT_BATCH)为true,故而会添加到一个ArrayList batch中,等到延迟时间到了,这200ms内所到达的所有hunter都会存储到batch中一并进行发送;来看具体的发送函数:
// Dispatcher
private static class DispatcherHandler extends Handler {
@Override public void handleMessage(final Message msg) {
switch (msg.what) {
case HUNTER_DELAY_NEXT_BATCH: {
dispatcher.performBatchComplete();
break;
}
}
}
}
void performBatchComplete() {
List copy = new ArrayList(batch);
batch.clear();
mainThreadHandler.sendMessage(mainThreadHandler.obtainMessage(HUNTER_BATCH_COMPLETE, copy));
logBatch(copy);
}
即通过主线程的Handler将结果发送到主线程;
mainThreadHandler对应的是Picasso中的静态内部类,来看其处理逻辑
//Picasso.java
static final Handler HANDLER = new Handler(Looper.getMainLooper()) {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case HUNTER_BATCH_COMPLETE: {
@SuppressWarnings("unchecked")
List batch = (List) msg.obj;
//noinspection ForLoopReplaceableByForEach
for (int i = 0, n = batch.size(); i < n; i++) {
BitmapHunter hunter = batch.get(i);
hunter.picasso.complete(hunter);
}
break;
}
}
}
}
继续来看complete:
//Picasso.java
void complete(BitmapHunter hunter) {
// 获取Action
Action single = hunter.getAction();
List joined = hunter.getActions();
boolean hasMultiple = joined != null && !joined.isEmpty();
boolean shouldDeliver = single != null || hasMultiple;
if (!shouldDeliver) {
return;
}
Uri uri = hunter.getData().uri;
Exception exception = hunter.getException();
Bitmap result = hunter.getResult();
LoadedFrom from = hunter.getLoadedFrom();
if (single != null) {
deliverAction(result, from, single);
}
if (hasMultiple) {
//noinspection ForLoopReplaceableByForEach
for (int i = 0, n = joined.size(); i < n; i++) {
Action join = joined.get(i);
deliverAction(result, from, join);
}
}
// 设置Listener情况
if (listener != null && exception != null) {
listener.onImageLoadFailed(this, uri, exception);
}
}
处理最终的结果,对于有合并相同Action的请求,则需要对应地分别进行处理;处理的函数均为deliverAction:
//Picasso.java
private void deliverAction(Bitmap result, LoadedFrom from, Action action) {
if (action.isCancelled()) {
return;
}
if (!action.willReplay()) {
targetToAction.remove(action.getTarget());
}
if (result != null) {
if (from == null) {
throw new AssertionError("LoadedFrom cannot be null.");
}
action.complete(result, from);
} else {
action.error();
}
}