Use Try-With-Resources instead of finally block when multiple lines in try block throws exception

Question

Code Snippet :

InputStream inputStream = null;
try{
    ExternalServiceObject object = externalService.getObject();
    inputStream = object.getInputStream();
    // further uses of inputStream
 } catch(Exception e){
   throw e;
  } finally {
        if(inputStream != null)
           inputStream.close();
  }

Here, externalService.getObject() can also throw an exception.

Wish to refactor this code using try-with-resources, hence avoiding the finally block. Or is the current behavior the most appropriate behavior.

All the comments and answers are appreciated.

If your question is about whether exception thrown inside resource declaration part of `try-with-resources` will be handled, then the answer is yes. You can try it with a relatively simple example - make your `externalService.getObject()` throw some exception and check whether `catch` block is executed. — Igor Nikolaev, Jan 05 '18 at 22:17
Yes, That is part of the question. Helped me understand try-with-resources. Thanks Much. — Kartavya Ramnani, Jan 05 '18 at 22:24

AJNeufeld · Accepted Answer · 2018-01-05T22:25:19.700

4

If you don't need the external service object for anything else:

try (InputStream inputStream = externalService.getObject().getInputStream()) {
    // further uses of inputStream
} catch (Exception e) {
    // ... logging etc
    throw e;
}

edited Jan 05 '18 at 22:25

answered Jan 05 '18 at 22:17

AJNeufeld

8,526
1
25
44

Excellent ! Elegant solution :') Thanks a lot. – Kartavya Ramnani Jan 05 '18 at 22:28

score 3 · Answer 2 · edited Jan 06 '18 at 08:46

3

I believe that execution order in the try-with-resources is top-down (like all other java variable definitions)

try
(
    ExternalServiceObject externalServiceObject = externalService.getObject(),
    InputStream inputStream = externalServiceObject.getInputStream();
)
{
    // further uses of inputStream
}
catch (Exception e)
{
    // do stuff.
}

Caveat: ExternalServiceObject must implement AutoCloseable

edited Jan 06 '18 at 08:46

Andy Turner

137,514
11
162
243

answered Jan 05 '18 at 22:23

DwB

37,124
11
56
82

+1 for the excellent Caveat. The external service is AWS S3Client, Wish I could tag them here. – Kartavya Ramnani Jan 05 '18 at 22:27

score 2 · Answer 3 · answered Jan 05 '18 at 22:16

2

So, use try-with-resources if that's what you want to use:

try {
  ExternalServiceObject object = externalService.getObject();
  try (InputStream inputStream = object.getInputStream()) {
    // ...
  }
} catch (Exception e) {
  throw e; // But why catch it only to rethrow?
}

answered Jan 05 '18 at 22:16

Andy Turner

137,514
11
162
243

Wont Having a try block inside a try block make the code look a little cluttered ? And Sorry, after catching the exception, logging is done and metrics are recorded, but I was too lazy to add the whole thing. Thanks so much. – Kartavya Ramnani Jan 05 '18 at 22:23
1

"look a little cluttered" If that's what you need, that's what you need. – Andy Turner Jan 05 '18 at 22:28
This code does not auto-close the `ExternalServiceObject`. – Basil Bourque Jan 05 '18 at 23:08
@Basil nor does OP's. The question doesn't make it clear that it needs to be closed. – Andy Turner Jan 06 '18 at 08:18

score 1 · Answer 4 · answered Jan 05 '18 at 22:15

The closing of the InputStream can be done using a try-with-resources block. It is more readable and less clunky. InputStream implements AutoCloseable and thus upon exiting a try-with-resources block the class's close method will automatically be called. If you are only using the InputStream for the scope of the try-catch-finally block then you should move it to the try block.

Also, you should avoid (where possible) catching Exception. Any resulting exceptions that are thrown in your try block could result in unwanted behavior.

Use Try-With-Resources instead of finally block when multiple lines in try block throws exception

4 Answers4