how to properly close resource streams in case of exceptions

Question

fortify is complaining about the following code:

protected void doStuff() throws Exception{
    try (CSVReader csvReader = new CSVReader(new FileReader(file))) {
        ...
        String[] read;
        read = csvReader.readNext();
        ...
    }
}

in the case that FileReader throws an exception. Im new to java, its unclear to me why the try with resources block doesnt handle the case. How to handle this?

It does. Fortify is just wrong (unless CSVReader doesn't close the reader it wraps when it's being closed, which would be surprising). — JB Nizet, Aug 29 '17 at 16:14
@JBNizet or if there is an exception thrown during construction of the `CSVReader`. — Andy Turner, Aug 29 '17 at 16:18
`fortify` may be too old to understand *try with resources* - not familiar with it. That construct in Java-6 would be a fail. — OldCurmudgeon, Aug 29 '17 at 16:21
What do you mean by complaining? If you're getting a syntax error, then your compiler is probably not compatible with Java SE 1.7. — Michael Peacock, Aug 29 '17 at 16:53
Fortify appears to be correct. As Andy said above, if CSVReader throws an exception, the FileReader will not be closed and its resources will leak. — Klitos Kyriacou, Aug 29 '17 at 16:57
does explicitly declaring the CSVReader and FileReader on seperate lines in the try statement solve this? — futevolei, Aug 29 '17 at 17:22
Yes. See this answer: https://stackoverflow.com/a/21348893/638028 — Klitos Kyriacou, Aug 29 '17 at 21:10

score 0 · Answer 1 · answered Aug 29 '17 at 17:04

It's always a good idea to close the lower level reader instance first and then close the wrapper level instance to avoid the memory leak.

So first close the instance of fileReader and then close instance of CSVReader.

FileReader fileReader= new FileReader(file)
CSVReader csvReader = new CSVReader(fileReader)


....
...
fileReader.close();
csvReader.close();

how to properly close resource streams in case of exceptions

1 Answers1