Java handle errors & exceptions

Question

I have a class that allows to download a file from the internet:

public String download(String URL) {

try {
 if(somethingbad) {
  // set an error?
  return false; 
 }
}
//...
catch (SocketException e) {
 e.printStackTrace();
}
catch (UnsupportedEncodingException e) {
 e.printStackTrace();
}
catch (ClientProtocolException e) {
 e.printStackTrace();
}
catch(InterruptedIOException e) {
e.printStackTrace();
}
catch (IOException e) {
 e.printStackTrace();
}
}

Now, I am calling this function in another class and i want to show a message that will help me figure out why this will not work.

what can i do to display something like this?

HTTPReq r = new HTTPReq("http://www.stack.com/api.json");    
if(r.err) {
 showMessage(getMessage());
}

and the getMessage() will return the SocketException or IOException or even "empty url" if the URL is empty.

Lazarus · Accepted Answer · 2015-01-08 17:19:51Z

2

First of all I do not think you need all these:

SocketException, UnsupportedEncodingException, ClientProtocolException since they extend IOException

but if you want you can do this:

public String download(String URL) throws IOException, Exception {

    try {
        if(somethingbad) {
            throws new Exception("My Message);
        }
    }
    catch (IOException e) {
        throw e;
    }
}

And then in your other file:

try {
    // some stuff
}
catch (Exception e) {
    // do something with e.getMessage();
}
catch (IOException e) {
    // do something with e.getMessage();
}

edited Jan 8, 2015 at 17:19

answered Jan 8, 2015 at 15:53

Lazarus

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1 Comment

vishal Over a year ago

catch(IOException) should go before catch(Exception). Otherwise IOExceptions will go into the first catch block.

vishal · Accepted Answer · 2015-01-07 18:07:55Z

2

Instead of just doing e.printStackTrace() inside the catch blocks, throw the exception back like so:

throw e;

Then you can surround the calling code like so:

try {
    HTTPReq r = new HTTPReq("http://www.stack.com/api.json");
} catch (Exception e) {
    // Show error message
}

answered Jan 7, 2015 at 18:07

vishal

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4 Comments

Erik Over a year ago

and i would just do : e.getMessage() from my other class?? Also, how would i trigger a getMessage() if the if(somethingbad) { fails?

vishal Over a year ago

You have to modify the signature of download method to indicate that it throws exceptions using the throws clause. An IDE should help you with the proper syntax.

Erik Over a year ago

I am using android studio and still don't get it

vishal Over a year ago

> and i would just do : e.getMessage() from my other class?? You could if you wanted to get the message inside the catch block. > Also, how would i trigger a getMessage() if the if(somethingbad) { fails? What sets the value of somethingbad? If download method throws an exception, the control will go into the appropriate catch block. The method will not continue to execute.

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