try-finally with close auto-refactoring to try-with-resources with codestyle/checkstyle

Question

I am working on a codebase that has recently migrated from Java 6 to Java 7. I would like to replace constructions like this:

Connection conn = null;
try{
    conn = new Connection();
    ...
} catch(Exception ex){
    ...
} finally{
    if (conn != null){
        conn.close();
    }
}

with try-with-resources (available from Java 1.7 onward):

try(Connection conn = new Connection()){
    ...
} catch(Exception ex){
    ...
}

Is there an automated way to automatically refactor the old to the new (perhaps with the Checkstyle-plugin, or within Eclipse itself)?

Answer 1

It would be difficult to change it all quickly. Please note that sometimes there's another try-catch block in finally which catches exceptions thrown while closing resource.

try-with-resources statement does allow you to handle resource closing exceptions (exceptions thrown at close method will be surpressed).

I haven't heard of such Eclipse feature, but if you may want to use IntelliJ IDEA Community Edition IDE just for this sole purpose.

#1

You can use code inspection features called:

1. 'try finally' replaceable with 'try' with resources.
2. AutoCloseable used without 'try' with resources

You should just press Ctrl+Alt+Shift, write inspection name and hit Enter. After that you will see places where IDEA can apply this pattern, but be aware that it doesn't cover 100% cases.

#2

Another way, more difficult, but greatly customizable is Structural Search and Replace functionality. You can define there structure which is to be changed:

try {
    $type$ $objectName$ = new $concreteType$($args$)
    $tryStatements$;
} catch($exceptionType$ $exceptionName$) {
    $catchStatements$;
} finally {
    $finallyStatements$;
}

And the final structure:

try ($type$ $objectName$ = new $concreteType$($args$)) {
  $tryStatements$;
} catch($exceptionType$ $exceptionName$) {
    $catchStatements$;
}

In variable settings you can require that $concreteType$ implements AutoCloseable interface.

But please note, that:

1. I get rid of finally block here and support single catch block.
2. There's also assumption that there would be single resource opened per one try-with-resources block.
3. As mentioned before - there's no exception handling in finally block.

This template certainly needs more work and it just may not be worthwhile to do it.