java尝试捕获阻止返回什么

Question

I have had a lot of fun using Gson from Google to parse Json this afternoon, but I was writing this code here:

public class Fetcher extends AsyncTask<String, Void, JsonReader> {

    @Override
    protected JsonReader doInBackground(String... urlString) {
        try {
            URL url = new URL(urlString[0]);
            BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream()));
            JsonReader jReader = new JsonReader(reader);
            return jReader;
        } catch(MalformedURLException malformedEx) {
            Log.e("malformed url: ", "here are the details: ", malformedEx);
        } catch(IOException ioEx) {
            Log.e("IO problem: ", "here are the details: ", ioEx);
        } catch(Exception generalEx) {
            Log.e("an exception we did not expect: ", "here are the details: ", generalEx);
        }

        //return statement here

    }
}

It is obviously going to complain that I am missing a return statement, but I am not sure what to return since I need to put the JsonReader in the try block and I can't just create an empty one since there is no constructor for it. I didn't think I would have to ask for this. Ideas please.

Answer 1

如果要捕获异常（确定要捕获？），则return null可能是正确的选择。

Answer 2

Since the method needs to return something and the try/catch can fail, you need to return something in the case of not being able to reach the return statement in the try/catch .

You should return null; or something that you want to return in case the try fails.

Answer 3

I think the best option should be

public class Fetcher extends AsyncTask<String, Void, JsonReader> {

    @Override
    protected JsonReader doInBackground(String... urlString) {

    JsonReader jReader = null;
        try {
            URL url = new URL(urlString[0]);
            BufferedReader reader = new BufferedReader(new InputStreamReader(url.openStream()));
            jReader = new JsonReader(reader);

        } catch(MalformedURLException malformedEx) {
            Log.e("malformed url: ", "here are the details: ", malformedEx);
        } catch(IOException ioEx) {
            Log.e("IO problem: ", "here are the details: ", ioEx);
        } catch(Exception generalEx) {
            Log.e("an exception we did not expect: ", "here are the details: ", generalEx);
        } finally {
           // CLOSE YOUR STREAMS
        }

        return jReader;

    }
}

But don't forget to test jreader before you use it or you can get a null pointer exception.

if (jReader!=null) {

//do something
}

Note: an explicit return null; is not a good programing practice, nor two return statements.