MyCache.java

import com.jakewharton.disklrucache.DiskLruCache;

import java.io.File;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class MyCache {

    DiskLruCache mDiskLruCache;

    public MyCache(File directory) throws IOException {
        mDiskLruCache = DiskLruCache.open(directory, 1, 1, 20 * 2^20);
    }

    public void put(String key, Object object) {
        DiskLruCache.Editor editor = null;
        try {
            editor = mDiskLruCache.edit(key);
            if (editor == null) {
                return;
            }

            ObjectOutputStream out = new ObjectOutputStream(editor.newOutputStream(0));
            out.writeObject(object);
            out.close();
            editor.commit();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public Object get(String key) {
        DiskLruCache.Snapshot snapshot;

        try {
            snapshot = mDiskLruCache.get(key);
            ObjectInputStream in = new ObjectInputStream(snapshot.getInputStream(0));
            return in.readObject();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException ex) {
            ex.printStackTrace();
        }
        return null;
    }

}

MyCacheTest.java

import android.content.Context;
import android.test.AndroidTestCase;
import android.test.IsolatedContext;

import java.io.File;
import java.util.ArrayList;
import java.util.List;

public class MyCacheTest extends AndroidTestCase {

    File mDirectory;
    MyCache myCache;

    public void setUp() throws Exception {
        Context context = getContext();
        IsolatedContext isolatedContext = new IsolatedContext(context.getContentResolver(), context);
        mDirectory = isolatedContext.getCacheDir();
        myCache = new MyCache(mDirectory);
    }

    public void tearDown() throws Exception {
        myCache.mDiskLruCache.delete();
        myCache.mDiskLruCache.close();
    }

    public void testPutGet() throws Exception {
        List<String> list = new ArrayList<String>();
        list.add("first string");
        list.add("second string");

        myCache.put("test-array-list", list);

        // Close and re-open the cache, forcing it to read from disk
        myCache.mDiskLruCache.close();
        myCache = new MyCache(mDirectory);

        List<String> actual = (List<String>) myCache.get("test-array-list");
        assertNotNull(actual); // test fails here
        assertEquals(list, actual);
    }

}