How do I handle exceptions in map() in an Observable in RxJava

Question

I want to do this:

Observable.just(bitmap)
            .map(new Func1<Bitmap, File>() {
                @Override
                public File call(Bitmap photoBitmap) {

                    //File creation throws IOException, 
                    //I just want it to hit the onError() inside subscribe()

                    File photoFile = new File(App.getAppContext().getCacheDir(), "userprofilepic_temp.jpg");
                    if(photoFile.isFile()) {//delete the file first if it exists otherwise the new file won't be created
                        photoFile.delete();
                    }
                    photoFile.createNewFile(); //saves the file in the cache dir

                    FileOutputStream fos = new FileOutputStream(photoFile);
                    photoBitmap.compress(Bitmap.CompressFormat.JPEG, 90, fos);//jpeg format
                    fos.close();

                    return photoFile;

                }
            })
            .subscribe(//continue implementation...);

Basically in the call() method, it can throw exceptions. How can I make the Observer handle it in onError(). Or is this not the right way to think about this?

Answer 1

rx will always catch error, even if this is RuntimeException. So you can throw Some kind of Runtime exception in catch block. This is how actually it should work.

 Observable.just(bitmap)
                .map(b -> {
                    try {
                        // do some work which throws IOException
                        throw new IOException("something went wrong");
                    } catch (IOException e) {
                        throw new RXIOException(e);
                        // Or you can use 
                        throw Exceptions.propagate(e);
                        // This helper method will wrap your exception with runtime one
                    }
                }).subscribe(o -> {
                    // do something here
                }, exception -> exception.printStackTrace());

public static class RXIOException extends RuntimeException {
        public RXIOException(IOException throwable) {
            super(throwable);
        }
}