disklrucache added to storage

Author: maciej-nowak

_drafts/2019-08-12-storage.md

@@ -154,32 +154,84 @@ Alternatywnym podejściem do implementacji pamięci podręcznej w stosunku do st
 {% highlight kotlin %}
 class LruCacheActivity : AppCompatActivity() {
 
-    //set key and value type
+    //set key and value type, it could be something heavy like Bitmap
     private lateinit var memoryCache : LruCache<String, String>
+    private lateinit var diskCache : DiskLruCache //external dependency
 
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
-        
+
+        //init cache before
         initMemoryCache()
-        useMemoryCache() //use some put, get, remove, resize method in memory
+        initDiskCache()
+
+        //combine memory and disk cache
+        writeToCache("key", "value")
+        readFromCache("key")
     }
 
     fun initMemoryCache() {
         //calculate max memory to 10% of available memory
         val maxMemory = (Runtime.getRuntime().maxMemory() / 1024).toInt()
-        
+
         memoryCache = object: LruCache<String, String>(maxMemory / 10) {
             override fun sizeOf(key: String, value: String): Int {
                 return value.toByteArray().size
             }
         }
     }
+
+    fun initDiskCache() {
+        val directory = File(cacheDir.path + File.separator + "lru") //use internal or external
+        val appVersion = 1 //
+        val valueCount = 1 //counter entries for every key
+        val maxSize = 1024L * 1024L * 10L //10MB of the cache
+        diskCache = DiskLruCache.open(directory, appVersion, valueCount, maxSize)
+    }
 
-    fun useMemoryCache() {
-        memoryCache.put("key", "some content like json")
-        val value = memoryCache.get("key")
-        memoryCache.remove("key")
-        memoryCache.resize(memoryCache.size() * 2)
+    fun writeToCache(key : String, value : String) {
+        if(readFromMemoryCache(key) == null) {
+            writeToMemoryCache(key, value)
+        }
+        writeToDiskCache(key, value)
+    }
+
+    fun readFromCache(key : String) : String? {
+        val result = readFromMemoryCache(key)
+        return if(result == null) {
+            readFromDiskCache(key)
+        } else result
+    }
+
+    fun writeToMemoryCache(key : String, value : String) {
+        memoryCache.put(key, value)
+    }
+
+    fun readFromMemoryCache(key : String) : String? {
+        return memoryCache.get(key)
+    }
+
+    fun writeToDiskCache(key : String, value : String) {
+        val editor : DiskLruCache.Editor? = diskCache.edit(key) //returns null if there is active editing
+        //begin the transaction for this key
+        editor?.let {
+            //the entry is mark as being edited
+            val output = it.newOutputStream(0)
+            output.write(value.toByteArray())
+            it.commit() //transaction has been finished
+        }
+    }
+
+    fun readFromDiskCache(key : String) : String? {
+        var value : String? = null
+        val snapshot : DiskLruCache.Snapshot? = diskCache.get(key) //returns null if entries doesn't exists
+        snapshot?.let {
+            val input = it.getInputStream(0)
+            val bytes = input.readBytes()
+            value = String(bytes) //decode bytes
+            it.close()
+        }
+        return value
     }
 }
 {% endhighlight %}