Android 框架修煉-自己封裝雙緩存管理框架庫

一、概述

　　Android開發中，網絡請求是很重要的一部分，而緩存網絡請求來的圖片或者響應結果字符串或者結果流，既可以省流量，同時也可以幫助我們

解決無網或弱網情況下加載情況，當然也可以提升程序性能效率。縱所周知，緩存管理中肯定需要用到內存緩存，這里我們采用LruCache來管理內存的緩存。

LruCahce雖然速度快，但是只是內存級別的緩存，為了實現持久化的緩存，我們還需要文件級別的緩存，也就是說我們要把緩存保存到文件，而文件則是保存

到手機存儲或者SD卡存儲中，即實現Disk級別的緩存，這里我們借助DiskLruCache這個輔助工具類來實現。顧名思義，這個工具類的作用就是使用Lru算法

來存儲信息到Disk上。

二、實例效果圖

　　下面是個簡單的實例演示效果圖

 

     

  

三、緩存管理框架的實現解

 

1、內存緩存類的實現

該類主要實現內存級別的緩存管理類MemoryCache，使用LruCache來實現，因為無論是內存緩存還是Disk緩存，都需要讀寫操作，

所以我們先抽象出一個緩存接口類：Cache接口：

public interface Cache {
    String get(final String key);
    void put(final String key, final String value);
    boolean remove(final String key);
}

然后，我們的內存緩存類MemoryCache需要實現Cache這個接口:

/**
 * 內存緩存類
 * Created by caizhiming on 2015/12/4.
 */
public class MemoryCache implements Cache {
    private LruCache<String, String> mMemoryLruCache;
    private EvictedListener mEvictedListener;

    public MemoryCache() {
        init();
    }

    public MemoryCache(EvictedListener listener) {
        init();
        this.mEvictedListener = listener;
    }

    public void setEvictedListener(EvictedListener listener) {
        this.mEvictedListener = listener;
    }

    public boolean hasEvictedListener() {
        return mEvictedListener != null;
    }

    private void init() {
        // 計算可使用的最大內存
        final int maxMemory = (int) (Runtime.getRuntime().maxMemory() / 1024);
        // 取可用內存空間的1/4作為緩存
        final int cacheSize = maxMemory / 4;
        mMemoryLruCache = new LruCache<String, String>(cacheSize) {
            @Override
            protected int sizeOf(String key, String value) {
                return value.getBytes().length;
            }

            @Override
            protected void entryRemoved(boolean evicted, String key, String oldValue, String newValue) {
                if (evicted) {
                    if (mEvictedListener != null) {
                        mEvictedListener.handleEvictEntry(key, oldValue);
                    }
                }
            }
        };
    }

    @Override
    public String get(String key) {
        return mMemoryLruCache.get(key);
    }

    @Override
    public void put(String key, String value) {
        mMemoryLruCache.put(key, value);
    }

    @Override
    public boolean remove(String key) {
        return Boolean.parseBoolean(mMemoryLruCache.remove(key));
    }

    /**
     * called when mMemoryLruCache evict entrys,
     * <p/>
     * using by CacheManager.Strategy.MEMORY_FIRST
     */
    public interface EvictedListener {
        void handleEvictEntry(String evictKey, String evictValue);
    }

2、文件級別的Disk緩存類實現

接下來我們需要寫一個用於Disk緩存管理的類：DiskCache類，該類我們也實現Cache接口，

該類的主要功能也是提供Disk緩存的讀取和寫入操作管理。

/**
 * Disk磁盤緩存類
 * Created by caizhiming on 2015/12/4.
 */
public class DiskCache implements Cache{

    private DiskLruCache mDiskLruCache = null;
    public DiskCache(Context context){
        init(context);
    }
    /**
     * 初始化 DiskLruCache
     */
    public void init(Context context){
        try {
            File cacheDir = getDiskCacheDir(context, "http_cache");
            if (!cacheDir.exists()) {
                cacheDir.mkdirs();
            }
            Log.v("czm", "cache file=" + cacheDir.getAbsolutePath());
            mDiskLruCache = DiskLruCache.open(cacheDir, getAppVersion(context), 1, 10 * 1024 * 1024);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    @Override
    public String get(String key) {
        String result = null;
        try {
            DiskLruCache.Snapshot snapShot = mDiskLruCache.get(hashKeyForDisk(key));
            if (snapShot != null) {
                result = snapShot.getString(0);
                return result;
            }
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }
        return result;
    }

    @Override
    public void put(String key, String value) {
        DiskLruCache.Editor editor = null;
        try {
            editor = mDiskLruCache.edit(hashKeyForDisk(key));
            if (editor != null) {
                editor.set(0, value);
                editor.commit();
            }
            mDiskLruCache.flush();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    @Override
    public boolean remove(String key) {
        try {
            return mDiskLruCache.remove(hashKeyForDisk(key));
        } catch (IOException e) {
            e.printStackTrace();
        }
        return false;
    }

    public Bitmap getImageCache(String key){
        Bitmap bitmap = null;
        try {
            DiskLruCache.Snapshot snapShot = mDiskLruCache.get(hashKeyForDisk(key));
            if (snapShot != null) {
                InputStream is = snapShot.getInputStream(0);
                bitmap = BitmapFactory.decodeStream(is);
                return bitmap;
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return bitmap;
    }
    public void putImageCache(final String key){
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    DiskLruCache.Editor editor = mDiskLruCache.edit(hashKeyForDisk(key));
                    if (editor != null) {
                        OutputStream outputStream = editor.newOutputStream(0);
                        if (downloadUrlToStream(key, outputStream)) {
                            editor.commit();
                        } else {
                            editor.abort();
                        }
                    }
                    mDiskLruCache.flush();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }
    private boolean downloadUrlToStream(String urlString, OutputStream outputStream) {
        HttpURLConnection urlConnection = null;
        BufferedOutputStream out = null;
        BufferedInputStream in = null;
        try {
            final URL url = new URL(urlString);
            urlConnection = (HttpURLConnection) url.openConnection();
            in = new BufferedInputStream(urlConnection.getInputStream(), 8 * 1024);
            out = new BufferedOutputStream(outputStream, 8 * 1024);
            int b;
            while ((b = in.read()) != -1) {
                out.write(b);
            }
            return true;
        } catch (final IOException e) {
            e.printStackTrace();
        } finally {
            if (urlConnection != null) {
                urlConnection.disconnect();
            }
            CloseUtils.closeCloseable(out);
            CloseUtils.closeCloseable(in);
        }
        return false;
    }


    public String hashKeyForDisk(String key) {
        String cacheKey;
        try {
            final MessageDigest mDigest = MessageDigest.getInstance("MD5");
            mDigest.update(key.getBytes());
            cacheKey = bytesToHexString(mDigest.digest());
        } catch (NoSuchAlgorithmException e) {
            cacheKey = String.valueOf(key.hashCode());
        }
        return cacheKey;
    }

    private String bytesToHexString(byte[] bytes) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < bytes.length; i++) {
            String hex = Integer.toHexString(0xFF & bytes[i]);
            if (hex.length() == 1) {
                sb.append('0');
            }
            sb.append(hex);
        }
        return sb.toString();
    }
    public File getDiskCacheDir(Context context, String uniqueName) {
        String cachePath;
        if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())
                || !Environment.isExternalStorageRemovable()) {
            cachePath = context.getExternalCacheDir().getPath();
        } else {
            cachePath = context.getCacheDir().getPath();
        }
        return new File(cachePath + File.separator + uniqueName);
    }

    public int getAppVersion(Context context) {
        try {
            PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
            return info.versionCode;
        } catch (PackageManager.NameNotFoundException e) {
            e.printStackTrace();
        }
        return 1;
    }


}

3、搭建封裝雙緩存管理框架類XCCacheManager

有了上面的內存緩存類MemoryCache和Disk緩存類DiskCache，我們就可以搭建封裝真正的緩存管理類XCCacheManager了。

（1）首先我們采用線程池技術來實現多線程緩存的讀寫操作

　　這樣可以提高程序的性能，同時能處理任務量比較大的並發讀寫操作。

private static XCCacheManager mInstance = null;

private Strategy mStrategy = Strategy.MEMORY_FIRST;
//線程池
private ExecutorService mExecutor = null;
//內存緩存
private MemoryCache mMemoryCache;
//Disk緩存
private DiskCache mDiskCache;

/**
     * 初始化 DiskLruCache
     */
    private void init(Context context) {
        mExecutor = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());
        mDiskCache = new DiskCache(context);
        mMemoryCache = new MemoryCache();
    }

（2）其次XCCacheManager管理類采用單例實現

public static XCCacheManager getInstance(Context context, Strategy strategy) {
    if (mInstance == null) {
        synchronized (XCCacheManager.class) {
            if (mInstance == null) {
                mInstance = new XCCacheManager(context.getApplicationContext(), strategy);
            }
        }
    } else {
        mInstance.setStrategy(strategy);
    }
    return mInstance;
}

（3）緩存策略

這里我們定義了緩存策略，便於適應各種不同業務需求，可以靈活使用不同的策略

public void setStrategy(XCCacheManager.Strategy strategy) {
    this.mStrategy = strategy;
    switch (mStrategy) {
        case MEMORY_FIRST:
            if (!mMemoryCache.hasEvictedListener()) {
                mMemoryCache.setEvictedListener(new MemoryCache.EvictedListener() {
                    @Override
                    public void handleEvictEntry(String evictKey, String evictValue) {
                        mDiskCache.put(evictKey, evictValue);
                    }
                });
            }
            break;
        case MEMORY_ONLY:
            if (mMemoryCache.hasEvictedListener())
                mMemoryCache.setEvictedListener(null);
            break;
        case DISK_ONLY:
            break;
    }
}

默認采用內存優先MEMORY_FIRST這種策略

（4）根據對應的策略從緩存中讀取內容

/**
 * 從緩存中讀取value
 */
public String readCache(final String key) {
    Future<String> ret = mExecutor.submit(new Callable<String>() {
        @Override
        public String call() throws Exception {
            String result = null;
            switch (mStrategy) {
                case MEMORY_ONLY:
                    result = mMemoryCache.get(key);
                    break;
                case MEMORY_FIRST:
                    result = mMemoryCache.get(key);
                    if (result == null) {
                        result = mDiskCache.get(key);
                    }
                    break;
                case DISK_ONLY:
                    result = mDiskCache.get(key);
                    break;
            }
            return result;
        }
    });
    try {
        return ret.get();
    } catch (InterruptedException e) {
        e.printStackTrace();
    } catch (ExecutionException e) {
        e.printStackTrace();
    }
    return null;
}

（5）將內容寫入到緩存中

/**
 * 將value 寫入到緩存中
 */
public void writeCache(final String key, final String value) {
    mExecutor.submit(new Runnable() {
        @Override
        public void run() {
            switch (mStrategy) {
                case MEMORY_FIRST:
                    mMemoryCache.put(key, value);
                    mDiskCache.put(key,value);
                    break;
                case MEMORY_ONLY:
                    mMemoryCache.put(key, value);
                    break;
                case DISK_ONLY:
                    mDiskCache.put(key, value);
                    break;
            }
        }
    });
}

 

到此為止，框架的開發到此完成。希望對有需要的人有所幫助。

四、源碼下載

源碼下載: www.demodashi.com/demo/12143.html

 真題園網：http://www.zhentiyuan.com