[英]How to store images in Cache Memory
我對此完全空白。 我想從 Url 下載圖像並且必須將其存儲在內部,以便下次我不需要連接到 web 而是從緩存 memory 中檢索它。 但我不知道該怎么做。 任何人都可以幫助我提供代碼片段。
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.StreamCorruptedException;
import java.text.SimpleDateFormat;
import java.util.HashMap;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Environment;
import android.util.Log;
public class CacheStore {
private static CacheStore INSTANCE = null;
private HashMap<String, String> cacheMap;
private HashMap<String, Bitmap> bitmapMap;
private static final String cacheDir = "/Android/data/com.yourbusiness/cache/";
private static final String CACHE_FILENAME = ".cache";
@SuppressWarnings("unchecked")
private CacheStore() {
cacheMap = new HashMap<String, String>();
bitmapMap = new HashMap<String, Bitmap>();
File fullCacheDir = new File(Environment.getExternalStorageDirectory().toString(),cacheDir);
if(!fullCacheDir.exists()) {
Log.i("CACHE", "Directory doesn't exist");
cleanCacheStart();
return;
}
try {
ObjectInputStream is = new ObjectInputStream(new BufferedInputStream(new FileInputStream(new File(fullCacheDir.toString(), CACHE_FILENAME))));
cacheMap = (HashMap<String,String>)is.readObject();
is.close();
} catch (StreamCorruptedException e) {
Log.i("CACHE", "Corrupted stream");
cleanCacheStart();
} catch (FileNotFoundException e) {
Log.i("CACHE", "File not found");
cleanCacheStart();
} catch (IOException e) {
Log.i("CACHE", "Input/Output error");
cleanCacheStart();
} catch (ClassNotFoundException e) {
Log.i("CACHE", "Class not found");
cleanCacheStart();
}
}
private void cleanCacheStart() {
cacheMap = new HashMap<String, String>();
File fullCacheDir = new File(Environment.getExternalStorageDirectory().toString(),cacheDir);
fullCacheDir.mkdirs();
File noMedia = new File(fullCacheDir.toString(), ".nomedia");
try {
noMedia.createNewFile();
Log.i("CACHE", "Cache created");
} catch (IOException e) {
Log.i("CACHE", "Couldn't create .nomedia file");
e.printStackTrace();
}
}
private synchronized static void createInstance() {
if(INSTANCE == null) {
INSTANCE = new CacheStore();
}
}
public static CacheStore getInstance() {
if(INSTANCE == null) createInstance();
return INSTANCE;
}
public void saveCacheFile(String cacheUri, Bitmap image) {
File fullCacheDir = new File(Environment.getExternalStorageDirectory().toString(),cacheDir);
String fileLocalName = new SimpleDateFormat("ddMMyyhhmmssSSS").format(new java.util.Date())+".PNG";
File fileUri = new File(fullCacheDir.toString(), fileLocalName);
FileOutputStream outStream = null;
try {
outStream = new FileOutputStream(fileUri);
image.compress(Bitmap.CompressFormat.PNG, 100, outStream);
outStream.flush();
outStream.close();
cacheMap.put(cacheUri, fileLocalName);
Log.i("CACHE", "Saved file "+cacheUri+" (which is now "+fileUri.toString()+") correctly");
bitmapMap.put(cacheUri, image);
ObjectOutputStream os = new ObjectOutputStream(new BufferedOutputStream(
new FileOutputStream(new File(fullCacheDir.toString(), CACHE_FILENAME))));
os.writeObject(cacheMap);
os.close();
} catch (FileNotFoundException e) {
Log.i("CACHE", "Error: File "+cacheUri+" was not found!");
e.printStackTrace();
} catch (IOException e) {
Log.i("CACHE", "Error: File could not be stuffed!");
e.printStackTrace();
}
}
public Bitmap getCacheFile(String cacheUri) {
if(bitmapMap.containsKey(cacheUri)) return (Bitmap)bitmapMap.get(cacheUri);
if(!cacheMap.containsKey(cacheUri)) return null;
String fileLocalName = cacheMap.get(cacheUri).toString();
File fullCacheDir = new File(Environment.getExternalStorageDirectory().toString(),cacheDir);
File fileUri = new File(fullCacheDir.toString(), fileLocalName);
if(!fileUri.exists()) return null;
Log.i("CACHE", "File "+cacheUri+" has been found in the Cache");
Bitmap bm = BitmapFactory.decodeFile(fileUri.toString());
bitmapMap.put(cacheUri, bm);
return bm;
}
}
雖然選擇的答案是正確的,但是它首先從服務器下載圖像有點冗長。 那些只是在尋找如何將 bitmap 保存到緩存中的人,我們可以使用 Android 的原生 LruCache 庫。 在這里,我寫了一篇關於LruCache in Java & LruCache in Kotlin的詳細文章。
Java Class 將 Bitmap 保存在緩存中:
import android.graphics.Bitmap;
import androidx.collection.LruCache;
public class MyCache {
private static MyCache instance;
private LruCache<Object, Object> lru;
private MyCache() {
lru = new LruCache<Object, Object>(1024);
}
public static MyCache getInstance() {
if (instance == null) {
instance = new MyCache();
}
return instance;
}
public LruCache<Object, Object> getLru() {
return lru;
}
public void saveBitmapToCahche(String key, Bitmap bitmap){
try {
MyCache.getInstance().getLru().put(key, bitmap);
}catch (Exception e){}
}
public Bitmap retrieveBitmapFromCache(String key){
try {
Bitmap bitmap = (Bitmap) MyCache.getInstance().getLru().get(key);
return bitmap;
}catch (Exception e){}
return null;
}
}
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