Develop Reference

Read Large File and Insert inside Room Database

I am making an app that blocks inappropriate websites for parental control, I have the blocked websites in a text file which 50MB in size. I want to add them all to room database so that I can check if a url is blocked or not.
But reading and looping through each line in the text file taking forever, is there any better way I can read the file and add each line to room database?
FileInputStream inputStream = null;
Scanner sc = null;
try {
inputStream = new FileInputStream(path);
sc = new Scanner(inputStream, "UTF-8");
while (sc.hasNextLine()) {
String line = sc.nextLine();
// insert to room database
}
// note that Scanner suppresses exceptions
if (sc.ioException() != null) {
throw sc.ioException();
}
} finally {
if (inputStream != null) {
inputStream.close();
}
if (sc != null) {
sc.close();
}
}

Make it as json and place it your project..
And when starting the application show a syncing state and load data to db ..
Do this only once.

You have a few options. As previously stated you could load the websites into json. This website should help automate that a bit. https://pdfmall.com/txt-to-json. This approach would still lead to an O(n) time complexity for searching.
While it will take a bit of memory, the method I'd recommend would be to build a custom object that holds all of those lines as Strings. Every time you start the app you would need to rebuild this object, but that's better than scanning constantly. You could implement an Async thread to do this in the background.
If you take this approach I would recommend storing them in a Olog(n) data structure like a binary tree. You don't want to just throw them into an Arraylist of strings, because then you'd be doing the same thing and having to scan through the entire array. If you store them in a tree, ordered by alphabetical order or perhaps length - whatever you want to do- then you reduce your search complexity from O(n) to Olog(n). Keep in mind when using custom objects, if you intend to pass them between Activities, you will need to implement Parcelable or another method.
Third you could use an Sql database, but in your case I don't believe this would speed anything up, so I wouldn't recommend it.

Keep the urls in the text file sorted alphabetically.
Load the file in a string array list.
Do a simple binary search in the sorted list to check for an specific url.

use stored JSON instead of Core Data

There are lots of tutorials out there describing how to fetch JSON objects from the web and map them to Core Data.
I'm currently working on an iOS (later: Android as well) app which loads json objects from web and displays them to the user. In my opinion all this mapping from and to Core Data is an overhead in this case, it would be much easier to save the JSON objects directly and use them as "cache" in the app. Are there libraries/documented ways how to achieve fetching json objects, save them locally and fetch them with a predefined identifier?
I would love to fetch e.g. 10 objects, show them to the user and save the data locally. The next time the user is on that list the local data is shown and in the background the json-file is fetched again to be up-to-date. I guess this is a common use case but I didn't find any tutorials/frameworks enabling exactly this.

You can simply use NSURLCache to cache http responses instead saving JSONs
http://nshipster.com/nsurlcache/

There are many ways to implement this. You can implement cache using either file storage or database depending on the complexity as well as quantity of your data. If you're using files, you just need to store JSON response and load it whenever activity/fragment is crated. What I have done sometimes is store the JSON response in the form of string in a file, and then retrieve it on activity/fragment load. Here's an example of reading and writing string files:
Writing files:
FileOutputStream outputStream = context.openFileOutput("myfilename",Context.MODE_PRIVATE);
String stringToBeSaved = myJSONObject.toString();
outputStream.write(stringToBeSaved.getBytes());
Reading from files
FileInputStream inputStream= context.openFileInput("myfilename");
int c;
String temp="";
while( (c = inputStream.read()) != -1){
temp = temp + Character.toString((char)c);
You can convert this string to JSONObject using :
JSONObject jsonObject = new JSONObject(temp);
Or you can use the string according to your needs.

What is the best way to store parsed json data

i would like to ask, how to store json data. I have a JSON file, which i parse using JSON Library. Now i got the data from a file. But i want to store them and show them later again.
The question is, whats the best way to store data? And is it even worth to store them?
I'm thinking about sql database, because its simple and most used.
Official android docs have few examples, so far i searched but if u have better guide, let me know.
Thank you! :)
EDIT1:
Ok, i have json file with data, which i can add to my app using RAW resources. Those data wont change, its a list of recipes, i dont have to download it. I can read the data like this:
InputStream is = mContext.getResources().openRawResource(R.raw.package_01);
Writer writer = new StringWriter();
char[] buffer = new char[1024];
try {
Reader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
int n;
while ((n = reader.read(buffer)) != -1) {
writer.write(buffer, 0, n);
}
is.close();
//catchblock
.....
}
and then i can parse the data trought JSONLibrary like this:
try {
//representing []JSON
JSONArray jsonArray = new JSONArray(writer.toString());
if(jsonArray != null){...}
...}
Im sending a HashMap to ListView, which includes name and id. And if the user clicks the ListView/GridView item, there is new Activity started, which shows all parsed data. I need to get match those parsed data with the id.
There are about 200 recipes in the file. The data are parsed on start of the Activity, while Splashscreen is displayed. I´m not sure, if its good idea to parse the data everytime when app starts.
So, is it effitient to parse data everytime the app starts? And if yes, how to keep the parsed data "together"? Should i use HashMap?
I hope i clarified my question :) Thanks for help.
EDIT2:
So after i knew what to do, i tried the suggested solution to use HashMap. Problem was there i got Failed Binder Exception. I have images encoded in Base64, that means i have a very long String, example here. That is a lot of data, there is limit:
The Binder transaction buffer has a limited fixed size, currently 1Mb, which is shared by all transactions in progress for the process.
I´ve tried to save it to
Set<String> titles = new HashSet<String>();
and then to SharedPreferences but the data for each recipe gets mixed.
**So, here it comes again, should i save the data to SQLite database or is there another effective option i can use? **
Thank you!

It really depends on a number of things like: How much data do you have now, how much will you have later, how complicated is the data. You could use something as simple as an array or hashmap; or something as complex as a database. You need to consider what you are trying to do , and find the simplest solution. If you are trying to persist data, you could use shared preferences, database, and internal/external storage (options outlined here).
Without more information it's hard to say what exactly to do. Keep it simple though. If you are getting JSON from a web service, I'd use an ArrayList or HashMap to store the data, rather than persisting it. It is simpler to implement and does the job.
EDIT:
To answer your question: Yes, using a HashMap and parsing each time is fine. You only have 200 fields, and you don't have images, so the time it will take to parse is minimal. Regardless of how you store the data, there is going to some level of "parsing" done. For example, if you store the data in a database, you are going to have to still pull the data, and put it into a HashMap.

Re-Using already fetched data from server in android

I am populating a listview with data(Text,image Urls etc) fetched from server.
This data might be updated at server side weekly/monthly.
What i want is , *when my application loads the listview first time, the data fetched from server is stored at application/client side, so as to be re-used later in redrawing the listview.*How can i acheive that.
One Possible Solution is:
Use Application class to download this data first time, store it in SQLlite db and always fetch results from DB while drawing a listview.Later i can use GCM Send-To-Sync tickles to update the sqldb data.
-Querying db everytime a listview is to be drawn, is it not a good practice.??
Any common practice to achieve this.
Any views about using Loaders/Loading Manager.
EDIT
The data in questions is a jsonpackage. With structure like(consider array size as 100 at max.)
[ // JSON Array
{ // JSON Object
"rank":1,"country":"China",
"population":"1,354,040,000",
"flag":"http://www.androidbegin.com/tutorial/flag/china.png"
}, (
]

Yes, you need to store the data fetched from server to database itself and then, bind the data from SQLiteDatabase to ListView
It cannot be said that Querying db everytime a listview is to be drawn, is it not a good practice.., because you need to fetch data only once when the activity is started or when the data within database is changed.
Re-Using already fetched data from server... means that you need a persistent storage and the storage should be updated periodically or on some user request.

It depends on what kind of data you have. Generally if it in a json package coming from the server then you can just keep that raw json and parse and populate the data on every app launch. But this will only be helpful if the amount of data is not too large. If the amount of data you have at any given moment is huge then you will have to parse and store the formatted data to a SQL DB, query and fetch the data on every app launch.
Also in case of manageable amount of data you can keep the data in-memory for the duration of the app lifecycle using static data model instances.
There can be multiple ways in which you can solve this problem but it all depends on how much data do you have and in what format and accordingly you take a call on which methodology will fetch you the best performance.

Create a directory in sdcard/internal storage, whichever is available using this static method.
/**
* Cache class to create dir, save, retrieve and delete files
* File names are hashCode of the url json is downloaded from.
**/
public class FileCache {
static File cacheDir;
static final String DIRECTORY_ADDRESS = "/Android/data/<app_package>/.<directory name>";
public static createDirectory(Context context){
if (android.os.Environment.getExternalStorageState().equals(android.os.Environment.MEDIA_MOUNTED))
cacheDir=new File(Environment.getExternalStorageDirectory(),DIRECTORY_ADDRESS);
else
cacheDir=context.getCacheDir();
if(!cacheDir.exists())
cacheDir.mkdirs();
}
public static File getFile(String url){
String filename=String.valueOf(url.hashCode());
File f = new File(cacheDir, filename);
return f;
}
public static void saveFile(InputStream is, File file){
try {
OutputStream os = new FileOutputStream(file);
copyStream(is, os);
os.close();
} catch (FileNotFoundException e) {
} catch (IOException e) {
}
}
/**
* Clear all files at app uninstall or application or on
* low memory or some other event, using a boradcastreceiver/alarmmanager
**/
public static void clear(){
File[] files=cacheDir.listFiles();
if(files==null)
return;
for(File f:files)
f.delete();
}
}
Now create directory when application starts:
FileCache.createDirectory(context);
Once this is set, you have to fetch your JSONArray using an AsyncTask, store store it in a file
/**
* Add this in doinBackground()
**/
private File getJson(Stirng url) {
File f = FileCache.getFile(url);
if(f != null && f.isFile()) {
//file exists in directory, no need to download.
return f;
}
try {
URL fileUrl = new URL(url);
HttpURLConnection conn = (HttpURLConnection) fileUrl.openConnection();
conn.setConnectTimeout(120000);
conn.setReadTimeout(120000);
conn.setInstanceFollowRedirects(true);
InputStream is = conn.getInputStream();
FileCache.saveFile(is, f);
return f;
} catch (Exception ex) {
return null;
}
}
Now you have to run this thread every time you need to load and bind the data into listview. I am excluding the details, of how you will parse the json from file and convert it into List for the Adapter.
This AsyncTask will automatically fetch the data if not available in file, and load into listview, in onPostExecute(). So, from the 2nd time, it wont take much time, and data will be persisted in storage. You can also add pagination in the ListView, i.e if you have 1000 json hashes, you can read data from this file in batches, that will also be a good optimization.
Now, whenever the data gets updated (monthly/weekly), send a push notification using GCM, run a service, clear the old file using FileCache.clear(), and start this AsyncTask from the service, all in the background, so if the app is opened afterwards, you will get updated data from file storage.
Putting everything in sqlite is a similar alternative, then you have to use DbAdapters, CursorLoaders and CursorAdapters, and then using the service to update the db.
But since you dont have large data sets, I think file caching is sufficient.
Hope that helps. :)

I implemented as below:
(If you see any issues in the implementation,performance wise or any please comment)
Fetch Data(Json Array with a length of 50 ) from server for first time, store it as a string(JsonArray.toString()) in sharedpreferences and populate the listview.
When required to display the listview again, get stored jsonarraystring from sharedpreferences ,convert it back to jsonarray and populate the listview.
To get updated data from server, send a GCM tickle to update stored sharedpreferences array with new value in background.
This approach is working fine so far. Do you guys see any issues i can face at anystage.
ThankYou

Android Out of Memory Error: How to solve this?

I have an application, and I am trying to set up a fairly large SQLite database (one table with roughly 5000 rows) into it. I have built the DB classes and everything, and my app works when I tested on a smaller scale (400 rows), but now when I want to import my database, I get the out of memory error which I can't seem to find a way to get around.
The database is initially on MySQL on my web server, and I couldn't convert it for some odd reason but I managed to generate a text file with the queries to add all 5000 rows, which is 11.5mb in size. I have this file in my assets folder, and I am trying this to put it into my DB:
public void onHandleIntent(Intent intent) {
DBAdapter db = new DBAdapter(getApplicationContext());
db.open();
try {
InputStream is = getAssets().open("verbs_sql.txt");
db.executeSQL(convertStreamToString(is));
} catch (IOException e) {}
db.close();
// Run main activity
Intent i = new Intent(DatabaseReceiver.this, BaseActivity.class);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS);
DatabaseReceiver.this.startActivity(i);
}
public static String convertStreamToString(InputStream is) throws IOException {
Writer writer = new StringWriter();
char[] buffer = new char[2048];
try {
Reader reader = new BufferedReader(new InputStreamReader(is, "UTF-8"));
int n;
while ((n = reader.read(buffer)) != -1) {
writer.write(buffer, 0, n);
}
} finally {
is.close();
}
String text = writer.toString();
return text;
}
}
The out of memory error occurs on the StringWriter(), so it looks likes it putting that big file on to the memory. How can I solve this? I have also tried looping through all 5000 rows but after maybe 30 seconds I got the out of memory again.

I had the same problem. I tried so many ways to solve it but failed. At last i found the reason and i wondered. In my case the reason for the error was i was printing the entire response string in log cat. That data was very huge and it took heap memory.
Take care of the following
Remove Log cat printing of bulk data.
Try to use only one J-SON Array for all Operation under one resonse(Reuse it for all).
Try to avoid array-list usage.
Insert item when each item iterate from J-Son Array. That means don't follow the method in which we are taking the item as object and put it in to an array-list and passing array-list to DB-helper and from there iterate the object and insert.

Sqlite databases are just files, when you're trying to run thousands of inserts on the phone you're hitting the SD card over and over for file access.
What you'll want to do is create the sqlite database on your desktop and include the already created database in the app. If you need to regularly update the information in the database you could post it on a website and have the app download it, just make sure to only do large downloads over Wifi.
Check out this Tech Talk for more information.
Edit: See this for more information on creating an sqlite database in windows and including it in your app.

I believe you could do this in the way you want. The problem with the code you posted is that you are trying to convert the entire file to a string. I am fairly certain that this would fail even on a desktop machine.
I believe that you would have better luck if you tried to read in one line at a time and execute the SQL. Then read the next line. You could also reduce the size of the file by passing it through zip.
If I can find a couple of minutes, I will attach some code.