SonarJava: TryWithResourcesCheck: try-with-resources is not equivalent to try-finally

[edp...@gmail.com]

try-with-resources is not equivalent to try-finally as try-with-resources will always throw any exception thrown from close, but that is not usually wanted.
There are important projects that are not migrating to try-with-resources because of this issue:
https://github.com/spring-projects/spring-framework/pull/1098

Migrating try-finally to try-with-resources may introduce bugs if the resource can throw exceptions on close

If there are strong arguments to remove TryWithResourcesCheck, the rule could be fixed by only suggesting the change when the resource close method does not throw any exception.

[Tibor Blenessy]

Hello,

there is no inherent issue to use try-with-resources, you can still have the catch block attached to it and you can catch the exception thrown from close and suppress it if necessary. The only difference is that close will be already called on all declared resources, which is especially useful when dealing with multiple resources.  You can find this behavior documented here   https://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html#suppressed-exceptions 

Hope that helps.

Tibor

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Tibor Blenessy | SonarSource

SonarJava Developer

https://sonarsource.com 

[edp...@gmail.com]

Hi Tibor,

I am not sure what you mean.
Here is a sample program.
Could you fix it so that the close exception is just logged, while exceptions in the try block are thrown?


public class TryWithResourcesTest {

    public static void main(String[] args) throws Exception {

        try (MyClosable a = new MyClosable()) {
            if (System.currentTimeMillis() % 2 == 0) {
                throw new RuntimeException("Exception on try block");
            }
        }

        System.out.println("Finished successfully");
    }

}

class MyClosable implements AutoCloseable {

    @Override
    public void close() throws Exception {
        throw new RuntimeException("Exception during close");
    }

}


Thanks

[Tibor Blenessy]

Hello,

have a look on this gist how this can be achieved

https://gist.github.com/saberduck/5bb8d91fb62614692d010458e62c7073 

Distinguishing by exception message is not ideal, however that's not an issue of try-with-resources. You can design your exceptions so they are more easily distinguishable. Also note that I don't need to close the resource in finally, as this is handled automatically. Especially with multiple resources this quickly becomes unwieldy with classic try-catch-finally statement.

How exactly this is done is described in detail in Java Language Specification, check it out here https://docs.oracle.com/javase/specs/jls/se8/html/jls-14.html#jls-14.20.3.1 

Anyhow, check is just a check. It should never be applied blindly and without consideration, that's why you can always mark issue as "wont fix" and provide a comment explaining the context.

Best regards

Tibor

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