Best Way to Cache Data in Android

Question

I have an ArrayList of custom, simple Serializable objects I would like to cache to disk and read on re-launch. My data is very small, about 25 object

Answer 1

For what it worth I cache some of my String data to disk using BufferedWriter/BufferedReader and it's very fast. Matter of fact it is faster than storing the same data to SharedPreferences. The code goes something like this (note that things happen faster when you provide buffer size)

final BufferedWriter out = new BufferedWriter(new FileWriter(file), 1024);
out.write(stuff);
out.close();

Answer 2

public class MyClass implements Serializable 
{
private static final long serialVersionUID = 1L;

public String title;
public String startTime;
public String endTime;
public String day;

public boolean classEnabled;


public MyClass(String title, String startTime, boolean enable) {
    this.title = title;
    this.startTime = startTime;
    this.classEnabled = enable;
}

public boolean saveObject(MyClass obj) {   
    final File suspend_f=new File(SerializationTest.cacheDir, "test");

    FileOutputStream   fos  = null;
    ObjectOutputStream oos  = null;
    boolean            keep = true;

    try {
        fos = new FileOutputStream(suspend_f);
        oos = new ObjectOutputStream(fos);
        oos.writeObject(obj);
    } catch (Exception e) {
        keep = false;
    } finally {
        try {
            if (oos != null)   oos.close();
            if (fos != null)   fos.close();
            if (keep == false) suspend_f.delete();
    } catch (Exception e) { /* do nothing */ }
    }

    return keep;
}

public MyClass getObject(Context c) {
    final File suspend_f=new File(SerializationTest.cacheDir, "test");

    MyClass simpleClass= null;
    FileInputStream fis = null;
    ObjectInputStream is = null;

    try {
        fis = new FileInputStream(suspend_f);
        is = new ObjectInputStream(fis);
        simpleClass = (MyClass) is.readObject();
    } catch(Exception e) {
        String val= e.getMessage();
    } finally {
        try {
            if (fis != null)   fis.close();
            if (is != null)   is.close();
        } catch (Exception e) { }
    }

    return simpleClass;  
}

and calling from activity

 if(android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
cacheDir=new File(android.os.Environment.getExternalStorageDirectory(),"MyCustomObject");
else
cacheDir= getCacheDir();
if(!cacheDir.exists())
cacheDir.mkdirs();

MyClass m = new MyClass("umer", "asif", true);
boolean result = m.saveObject(m);

if(result)
Toast.makeText(this, "Saved object", Toast.LENGTH_LONG).show();

else
Toast.makeText(this, "Error saving object", Toast.LENGTH_LONG).show();   

 MyClass m = new MyClass();
 MyClass c = m.getObject(this);

 if(c!= null)

 Toast.makeText(this, "Retrieved object", Toast.LENGTH_LONG).show();

  else

 Toast.makeText(this, "Error retrieving object", Toast.LENGTH_LONG).show();

dont forget to use write_external_storage permissions in manifest file.

Answer 3

It's hard to know without profiling but my guess is your poor performance is down to using ObjectOutputStream. Have you tried writing your own writeObject(ObjectOutputStream) and readObject(ObjectOutputStream) methods as this may help performance.

You could use the traceview tool to see exactly where the application is running slow. Have a look at this question for instructions on how to use traceview.