ObjectStore.java

/*
* Copyright 2021 Nandan Desai

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
* 
* */

import android.content.Context;


import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.Map;

public class ObjectStore<T> {

    private LRUMap<String, T> lruMap=null;
    private String storeName;
    private String cacheStoragePath;
    public ObjectStore(Context context, String storeName, int size) throws IOException {
        this.cacheStoragePath=context.getCacheDir()+"/.mycachestore";
        File cacheDir = new File(cacheStoragePath);
        if(cacheDir.exists()){
            System.out.println("Cache dir exists!");
            loadStoreFile(storeName, size);
        }else{
            System.out.println("Cache dir doesn't exists. Creating a new one.");
            if(cacheDir.mkdirs()) {
                loadStoreFile(storeName, size);
            }else{
                throw new IOException("couldn't create cache directory");
            }
        }
        this.storeName=storeName;
    }

    private void loadStoreFile(String storeName, int size){
        File storeFile=new File(cacheStoragePath+"/"+storeName);
        lruMap=new LRUMap<>(size);
        if(storeFile.exists()) {
            System.out.println("cache store file already exists! Loading it to memory now.");
            try {
                FileInputStream file = new FileInputStream(cacheStoragePath+"/"+storeName);
                ObjectInputStream in = new ObjectInputStream(file);

                // Method for deserialization of object
                lruMap = (LRUMap<String, T>)in.readObject();

                in.close();
                file.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
            ;
        }
    }

    public void persist(){
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    FileOutputStream file = new FileOutputStream(cacheStoragePath + "/" + storeName);
                    ObjectOutputStream out = new ObjectOutputStream(file);

                    out.writeObject(lruMap);

                    out.close();
                    file.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }
                System.out.println("wrote cache data from memory to disk and closed it!");
            }
        }).start();
    }

    public T get(String key){
        return lruMap.get(key);
    }

    public ArrayList<T> getAll(){
        ArrayList<T> list=new ArrayList<>();
        Iterator<T> iterator=lruMap.values().iterator();
        while (iterator.hasNext()){
            list.add(iterator.next());
        }
        Collections.reverse(list);
        return list;
    }

    public void put(String key, T value){
        lruMap.put(key, value);
    }

    public void delete(String key){
        lruMap.remove(key);
    }

    private static class LRUMap<K, V> extends LinkedHashMap<K, V> implements Serializable {
        private int size=10;

        LRUMap(int size) {
            super(size, 0.75f, true);
            this.size = size;
        }

        LRUMap() {}


        @Override
        protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
            return size() > size;
        }

    }
}