Android/DiskLruCache

準備

以下追加

• app/build.gradle

dependencies {
    implementation 'com.jakewharton:disklrucache:2.0.2'
}

公式?

https://github.com/JakeWharton/DiskLruCache

google https://android.googlesource.com/platform/libcore/+/jb-mr2-release/luni/src/main/java/libcore/io/DiskLruCache.java

okhttp3 https://github.com/square/okhttp/blob/master/okhttp/src/main/java/okhttp3/internal/cache/DiskLruCache.java

mopub https://github.com/mopub/mopub-android-sdk/blob/master/mopub-sdk/mopub-sdk-base/src/main/java/com/mopub/common/DiskLruCache.java

使い方サンプル

String UNIQUE_CACHE_NAME = "hogehoge-cache";
int VALUE_COUNT = 1;
int DISK_CACHE_INDEX = 0;
String cachePath = context.getCacheDir().getPath()
File cacheDirectory =  new File(cachePath + File.separator + UNIQUE_CACHE_NAME);
long diskCacheSizeBytes = 30 * 1024 * 1024; // 30 MB
// 初期化
DiskLruCache sDiskLruCache = DiskLruCache.open(
                        cacheDirectory,
                        APP_VERSION,
                        VALUE_COUNT,
                        diskCacheSizeBytes);
// 取得
DiskLruCache.Snapshot snapshot = sDiskLruCache.get("hogehoge");
final InputStream in = snapshot.getInputStream(DISK_CACHE_INDEX);

// 更新
DiskLruCache.Editor editor = sDiskLruCache.edit("hogehoge");
final OutputStream outputStream =
        new BufferedOutputStream(editor.newOutputStream(DISK_CACHE_INDEX));
Streams.copyContent(content, outputStream);
outputStream.flush();
outputStream.close();
sDiskLruCache.flush();
editor.commit();

// 削除
sDiskLruCache.delete()

mopubに上記コードの詳細がある https://github.com/mopub/mopub-android-sdk/blob/master/mopub-sdk/mopub-sdk-base/src/main/java/com/mopub/common/CacheService.java

key部分のhogehogeはmd5やsha1などでhash化して使うと良い。

downloadしたものをcacheする

URL u = new URL(mUrl);
InputStream is = u.openStream();
HttpURLConnection huc = (HttpURLConnection)u.openConnection();
int size = huc.getContentLength();
if (huc != null) {
    InputStream inputStream = new BufferedInputStream(huc.getInputStream());
    boolean diskPutResult = CacheService.putToDiskCache(sha1(mUrl), inputStream);
}
<pre>

==permission追加==
保存場所はconstructのparamで指定するので、適宜記述となる。

mopubではcontext.getCacheDir()を使っておりAndroidManifestのpermissionは不要だった。
https://github.com/mopub/mopub-android-sdk/blob/master/mopub-sdk/mopub-sdk-base/src/main/java/com/mopub/common/CacheService.java

context.getExternalCacheDir()をもし使う場合はKitKatからpermission不要となったが、それ以前では必要なので以下のように追加する
<pre>
<uses-permission
    android:name="android.permission.WRITE_EXTERNAL_STORAGE"
    android:maxSdkVersion="18" />

http://wada811.blogspot.com/2014/09/storage-access-and-permission-in-android.html

https://developer.android.com/training/data-storage/files