read file from assets

Question

public class Utils {
    public static List<Message> getMessages() {
        //File file = new File("file:///android_asset/helloworld.txt");
        AssetManager assetManager = getAssets();
        InputStream ims = assetManager.open("helloworld.txt");    
     }
}

I am using this code trying to read a file from assets. I tried two ways to do this. First, when use File I received FileNotFoundException, when using AssetManager getAssets() method isn't recognized. Is there any solution here?

Answer 1

getAssets()

is only works in Activity in other any class you have to use Context for it.

Make a constructor for Utils class pass reference of activity (ugly way) or context of application as a parameter to it. Using that use getAsset() in your Utils class.

Answer 2

In MainActivity.java

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView tvView = (TextView) findViewById(R.id.tvView);

        AssetsReader assetsReader = new AssetsReader(this);
        if(assetsReader.getTxtFile(your_file_title)) != null)
        {
            tvView.setText(assetsReader.getTxtFile(your_file_title)));
        }
    }

Also, you can create separate class that does all the work

public class AssetsReader implements Readable{

    private static final String TAG = "AssetsReader";


    private AssetManager mAssetManager;
    private Activity mActivity;

    public AssetsReader(Activity activity) {
        this.mActivity = activity;
        mAssetManager = mActivity.getAssets();
    }

    @Override
    public String getTxtFile(String fileName)
    {
        BufferedReader reader = null;
        InputStream inputStream = null;
        StringBuilder builder = new StringBuilder();

        try{
            inputStream = mAssetManager.open(fileName);
            reader = new BufferedReader(new InputStreamReader(inputStream));

            String line;

            while((line = reader.readLine()) != null)
            {
                Log.i(TAG, line);
                builder.append(line);
                builder.append("\n");
            }
        } catch (IOException ioe){
            ioe.printStackTrace();
        } finally {

            if(inputStream != null)
            {
                try {
                    inputStream.close();
                } catch (IOException ioe){
                    ioe.printStackTrace();
                }
            }

            if(reader != null)
            {
                try {
                    reader.close();
                } catch (IOException ioe)
                {
                    ioe.printStackTrace();
                }
            }
        }
        Log.i(TAG, "builder.toString(): " + builder.toString());
        return builder.toString();
    }
}

In my opinion it's better to create an interface, but it's not neccessary

public interface Readable {
    /**
     * Reads txt file from assets
     * @param fileName
     * @return string
     */
    String getTxtFile(String fileName);
}

Answer 3

You can load the content from the file. Consider the file is present in asset folder.

public static InputStream loadInputStreamFromAssetFile(Context context, String fileName){
    AssetManager am = context.getAssets();
    try {
        InputStream is = am.open(fileName);
        return is;
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

public static String loadContentFromFile(Context context, String path){
    String content = null;
    try {
        InputStream is = loadInputStreamFromAssetFile(context, path);
        int size = is.available();
        byte[] buffer = new byte[size];
        is.read(buffer);
        is.close();
        content = new String(buffer, "UTF-8");
    } catch (IOException ex) {
        ex.printStackTrace();
        return null;
    }
    return content;
}

Now you can get the content by calling the function as follow

String json= FileUtil.loadContentFromFile(context, "data.json");

Considering the data.json is stored at Application\app\src\main\assets\data.json

Answer 4

If you use other any class other than Activity, you might want to do like,

BufferedReader bufferedReader = new BufferedReader(new InputStreamReader( YourApplication.getInstance().getAssets().open("text.txt"), "UTF-8"));

Answer 5

Here is what I do in an activity for buffered reading extend/modify to match your needs

BufferedReader reader = null;
try {
    reader = new BufferedReader(
        new InputStreamReader(getAssets().open("filename.txt")));

    // do reading, usually loop until end of file reading  
    String mLine;
    while ((mLine = reader.readLine()) != null) {
       //process line
       ...
    }
} catch (IOException e) {
    //log the exception
} finally {
    if (reader != null) {
         try {
             reader.close();
         } catch (IOException e) {
             //log the exception
         }
    }
}

EDIT : My answer is perhaps useless if your question is on how to do it outside of an activity. If your question is simply how to read a file from asset then the answer is above.

UPDATE :

To open a file specifying the type simply add the type in the InputStreamReader call as follow.

BufferedReader reader = null;
try {
    reader = new BufferedReader(
        new InputStreamReader(getAssets().open("filename.txt"), "UTF-8")); 

    // do reading, usually loop until end of file reading 
    String mLine;
    while ((mLine = reader.readLine()) != null) {
       //process line
       ...
    }
} catch (IOException e) {
    //log the exception
} finally {
    if (reader != null) {
         try {
             reader.close();
         } catch (IOException e) {
             //log the exception
         }
    }
}

EDIT

As @Stan says in the comment, the code I am giving is not summing up lines. mLine is replaced every pass. That's why I wrote //process line. I assume the file contains some sort of data (i.e a contact list) and each line should be processed separately.

In case you simply want to load the file without any kind of processing you will have to sum up mLine at each pass using StringBuilder() and appending each pass.

ANOTHER EDIT

According to the comment of @Vincent I added the finally block.

Also note that in Java 7 and upper you can use try-with-resources to use the AutoCloseable and Closeable features of recent Java.

CONTEXT

In a comment @LunarWatcher points out that getAssets() is a class in context. So, if you call it outside of an activity you need to refer to it and pass the context instance to the activity.

ContextInstance.getAssets();

This is explained in the answer of @Maneesh. So if this is useful to you upvote his answer because that's him who pointed that out.

Answer 6

Better late than never.

I had difficulties reading files line by line in some circumstances. The method below is the best I found, so far, and I recommend it.

Usage: String yourData = LoadData("YourDataFile.txt");

Where YourDataFile.txt is assumed to reside in assets/

 public String LoadData(String inFile) {
        String tContents = "";

    try {
        InputStream stream = getAssets().open(inFile);

        int size = stream.available();
        byte[] buffer = new byte[size];
        stream.read(buffer);
        stream.close();
        tContents = new String(buffer);
    } catch (IOException e) {
        // Handle exceptions here
    }

    return tContents;

 }