private String getKeyFromUrl(String url) {
String key;
try {
MessageDigest messageDigest = MessageDigest.getInstance("MD5");
messageDigest.update(url.getBytes());
byte[] m = messageDigest.digest();
return getString(m);
} catch (NoSuchAlgorithmException e) {
key = String.valueOf(url.hashCode());
}
return key;
}
private static String getString(byte[] b){
StringBuffer sb = new StringBuffer();
for(int i = 0; i < b.length; i ++){
sb.append(b[i]);
}
return sb.toString();
}
得到了key后，我们可以使用put方法向LruCache内部的LinkedHashMap中添加缓存对象，这个方法的源码如下：
public final V put(K key, V value) {
if (key == null || value == null) {
throw new NullPointerException("key == null || value == null");
}
V previous;
synchronized (this) {
putCount++;
size += safeSizeOf(key, value);
previous = map.put(key, value);
if (previous != null) {
size -= safeSizeOf(key, previous);
}
}
if (previous != null) {
entryRemoved(false, key, previous, value);
}
trimToSize(maxSize);
return previous;
}
从以上代码我们可以看到这个方法确实也作了同步，它将新的key-value对放入LinkedHashMap后会返回相应key原来对应的value。
（4）删除缓存对象
我们可以通过remove方法来删除缓存对象，这个方法的源码如下：
public final V remove(K key) {
if (key == null) {
throw new NullPointerException("key == null");
}
V previous;
synchronized (this) {
previous = map.remove(key);
if (previous != null) {
size -= safeSizeOf(key, previous);
}
}
if (previous != null) {
entryRemoved(false, key, previous, null);
}
return previous;
}
