ImageLoader源码分析（一）ImageLoader初始化
ImageLoader加载图片前要初始化，初始化时需要一个 ImageLoaderConfiguration
初始化代码：
ImageLoader.getInstance().init(configuration);
ImageLoaderConfiguration实例有两种默认创建方式：
1. ImageLoaderConfiguration configuration1= ImageLoaderConfiguration.createDefault(context);
2. ImageLoaderConfiguration configuration2=new ImageLoaderConfiguration.Builder(context).build();
在源码ImageLoaderConfiguration类中可以看到：
public static ImageLoaderConfiguration createDefault(Context context) {
return new Builder(context).build();
}
所以上面两种初始化方式效果是一样的。
再来看一下Builder相关代码：
Builder构造函数：
public Builder(Context context) {
this.context = context.getApplicationContext();
}
Builder中builder()方法相关代码：
/** Builds configured {@link ImageLoaderConfiguration} object */
public ImageLoaderConfiguration build() {
initEmptyFieldsWithDefaultValues();
return new ImageLoaderConfiguration(this);
}
private void initEmptyFieldsWithDefaultValues() {
if (taskExecutor == null) {
taskExecutor = DefaultConfigurationFactory
.createExecutor(threadPoolSize, threadPriority, tasksProcessingType);
} else {
customExecutor = true;
}
if (taskExecutorForCachedImages == null) {
taskExecutorForCachedImages = DefaultConfigurationFactory
.createExecutor(threadPoolSize, threadPriority, tasksProcessingType);
} else {
customExecutorForCachedImages = true;
}
if (diskCache == null) {
if (diskCacheFileNameGenerator == null) {
diskCacheFileNameGenerator = DefaultConfigurationFactory.createFileNameGenerator();
}
diskCache = DefaultConfigurationFactory
.createDiskCache(context, diskCacheFileNameGenerator, diskCacheSize, diskCacheFileCount);
}
if (memoryCache == null) {
memoryCache = DefaultConfigurationFactory.createMemoryCache(context, memoryCacheSize);
}
if (denyCacheImageMultipleSizesInMemory) {
memoryCache = new FuzzyKeyMemoryCache(memoryCache, MemoryCacheUtils.createFuzzyKeyComparator());
}
if (downloader == null) {
downloader = DefaultConfigurationFactory.createImageDownloader(context);
}
if (decoder == null) {
decoder = DefaultConfigurationFactory.createImageDecoder(writeLogs);
}
if (defaultDisplayImageOptions == null) {
defaultDisplayImageOptions = DisplayImageOptions.createSimple();
}
}
我们看到有这么一句话：
if (memoryCache == null) {
memoryCache = DefaultConfigurationFactory.createMemoryCache(context, memoryCacheSize);
}
在DefaultConfigurationFactory.createMemoryCache中我们发现默认内存缓存使用的是自定义的LruMemoryCache（最近最少使用算法Least Recently Used）,其源码如下
package com.nostra13.universalimageloader.cache.memory.impl;
import android.graphics.Bitmap;
import com.nostra13.universalimageloader.cache.memory.MemoryCache;
import java.util.Collection;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.Map;
/**
* A cache that holds strong references to a limited number of Bitmaps. Each time a Bitmap is accessed, it is moved to
* the head of a queue. When a Bitmap is added to a full cache, the Bitmap at the end of that queue is evicted and may
* become eligible for garbage collection.<br />
* <br />
* <b>NOTE:</b> This cache uses only strong references for stored Bitmaps.
*
* @author Sergey Tarasevich (nostra13[at]gmail[dot]com)
* @since 1.8.1
*/
public class LruMemoryCache implements MemoryCache {
private final LinkedHashMap<String, Bitmap> map;
private final int maxSize;
/** Size of this cache in bytes */
private int size;
/** @param maxSize Maximum sum of the sizes of the Bitmaps in this cache */
public LruMemoryCache(int maxSize) {
if (maxSize <= 0) {
throw new IllegalArgumentException("maxSize <= 0");
}
this.maxSize = maxSize;
this.map = new LinkedHashMap<String, Bitmap>(0, 0.75f, true);
}
/**
* Returns the Bitmap for {@code key} if it exists in the cache. If a Bitmap was returned, it is moved to the head
* of the queue. This returns null if a Bitmap is not cached.
*/
@Override
public final Bitmap get(String key) {
if (key == null) {
throw new NullPointerException("key == null");
}
synchronized (this) {
return map.get(key);
}
}
/** Caches {@code Bitmap} for {@code key}. The Bitmap is moved to the head of the queue. */
@Override
public final boolean put(String key, Bitmap value) {
if (key == null || value == null) {
throw new NullPointerException("key == null || value == null");
}
synchronized (this) {
size += sizeOf(key, value);
Bitmap previous = map.put(key, value);
if (previous != null) {
size -= sizeOf(key, previous);
}
}
trimToSize(maxSize);
return true;
}
/**
* Remove the eldest entries until the total of remaining entries is at or below the requested size.
*
* @param maxSize the maximum size of the cache before returning. May be -1 to evict even 0-sized elements.
*/
private void trimToSize(int maxSize) {
while (true) {
String key;
Bitmap value;
synchronized (this) {
if (size < 0 || (map.isEmpty() && size != 0)) {
throw new IllegalStateException(getClass().getName() + ".sizeOf() is reporting inconsistent results!");
}
if (size <= maxSize || map.isEmpty()) {
break;
}
Map.Entry<String, Bitmap> toEvict = map.entrySet().iterator().next();
if (toEvict == null) {
break;
}
key = toEvict.getKey();
value = toEvict.getValue();
map.remove(key);
size -= sizeOf(key, value);
}
}
}
/** Removes the entry for {@code key} if it exists. */
@Override
public final Bitmap remove(String key) {
if (key == null) {
throw new NullPointerException("key == null");
}
synchronized (this) {
Bitmap previous = map.remove(key);
if (previous != null) {
size -= sizeOf(key, previous);
}
return previous;
}
}
@Override
public Collection<String> keys() {
synchronized (this) {
return new HashSet<String>(map.keySet());
}
}
@Override
public void clear() {
trimToSize(-1); // -1 will evict 0-sized elements
}
/**
* Returns the size {@code Bitmap} in bytes.
* <p/>
* An entry's size must not change while it is in the cache.
*/
private int sizeOf(String key, Bitmap value) {
return value.getRowBytes() * value.getHeight();
}
@Override
public synchronized final String toString() {
return String.format("LruCache[maxSize=%d]", maxSize);
}
}
我们发现使用的是java.util.LinkedHashMap<String, Bitmap>来存储Bitmap，并且是强引用，并没用采用软引用或弱引用。
再看这句话:
if (diskCache == null) {
if (diskCacheFileNameGenerator == null) { //文件名生成器，源码中使用的是url的哈希值
diskCacheFileNameGenerator = DefaultConfigurationFactory.createFileNameGenerator();
}
diskCache = DefaultConfigurationFactory.createDiskCache(context, diskCacheFileNameGenerator, diskCacheSize, diskCacheFileCount);
}
当diskCacheSize>0或者diskCacheFileCount>0时使用的是自定义 的LruDiskCache，否则是UnlimitedDiskCache。
我们在builder中还看到这样一句代码：
if (downloader == null) {
downloader = DefaultConfigurationFactory.createImageDownloader(context);
}
在DefaultConfigurationFactory.createImageDownloader中我们看到使用的下载类是BaseImageDownloader，并重写了ImageDownloader接口中的getStream方法，BaseImageDownloader中我们看到了如下相关代码：
protected InputStream getStreamFromNetwork(String imageUri, Object extra) throws IOException {
HttpURLConnection conn = createConnection(imageUri, extra);
int redirectCount = 0;
//请求重定向
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());
}
所以ImageLoader默认使用的网络请求是 HttpURLConnection，所以我们可以很方便的修改为自定义的网络请求，如使用okhttp等。
ImageLoader中默认采用BaseImageDecoder，可以矫正图像（旋转等）。
所以如果我们不想使用默认 的配置初始化，我们可以这样初始化：
ImageLoaderConfiguration.Builder builder=new ImageLoaderConfiguration.Builder(context);
builder.imageDownloader(new ImageDownloader() {
/**
* @param imageUri 图片url
*
* @param extra 可以忽略不使用
*/
@Override
public InputStream getStream(String imageUri, Object extra) throws IOException {
//使用第三方网络请求类库下载图片
return null;
}
});
//采用软引用
builder.memoryCache(new BaseMemoryCache() {
@Override
protected Reference<Bitmap> createReference(Bitmap value) {
return new SoftReference<Bitmap>(value);
}
});
builder.threadPoolSize(5);
//省去部分自定义。。。。
ImageLoader.getInstance().init(builder.build());
注意：builder.build(); 中已经判断是否为null了，所以默认值不会覆盖用户自定义的配置