FindBugs - "may fail to close stream" when using ObjectOutputStream

Question

I have this piece of code, which is to write an Ojbect to a byte array stream:

     static byte[] toBytes(MyTokens tokens) throws IOException {
        ByteArrayOutputStream out = null;
        ObjectOutput s = null;
        try {
            out = new ByteArrayOutputStream();
            try {
                s = new ObjectOutputStream(out);
                s.writeObject(tokens);
            } finally {
                try {
                    s.close();
                } catch (Exception e) {
                    throw new CSBRuntimeException(e);
                }             
            }
        } catch (Exception e) {
            throw new CSBRuntimeException(e);
        } finally {
            IOUtils.closeQuietly(out);
        }
        return out.toByteArray();
    }

However, FindBugs keeps complaining about line:

s = new ObjectOutputStream(out);

that "may fail to close stream" - BAD_PRACTICE - OS_OPEN_STREAM. Can somebody help?

If you are using Java 7, you can use [try-with-resources](http://docs.oracle.com/javase/tutorial/essential/exceptions/tryResourceClose.html). — Duncan Jones, Jan 21 '13 at 07:59
Just FYI - I'm unable to get my FindBugs to complain about your code. I'm using the latest FindBugs Eclipse, with the reporting level set to 20 (the least concerning) and every category enabled. What version of FindBugs are you using and how are you executing it? — Duncan Jones, Jan 21 '13 at 08:12
I'm using Eclipse 3.7 with Maven, hence findbugs-maven-plugin:2.5.2 is used. Running it with "mvn site" for the bug reporting. — Eugene, Jan 21 '13 at 08:42

Evgeniy Dorofeev · Accepted Answer · 2013-01-21T08:34:35.377

9

I think FindBugs does not undestand that IOUtils.closeQuietly(out) closes out.

Anyway it is enough to close ObjectOutputStream and it will close underlying ByteArrayOutputStream. This is ObjectOutputStream.close implementation

public void close() throws IOException {
    flush();
    clear();
    bout.close();
}

so you can simplify your code

    ByteArrayOutputStream out = new ByteArrayOutputStream();
    ObjectOutputStream s = new ObjectOutputStream(out);
    try {
        s.writeObject(1);
    } finally {
        IOUtils.closeQuietly(s);
    }

or if you are in Java 7

    ByteArrayOutputStream out = new ByteArrayOutputStream();
    try (ObjectOutputStream s = new ObjectOutputStream(out)) {
        s.writeObject(1);
    }

edited Jan 21 '13 at 08:34

answered Jan 21 '13 at 07:58

Evgeniy Dorofeev

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I already tried this, but IOUtils.closeQuietly() just does not work with ObjectOutput, so it cannot close "s". It's only allow OutputStream... – Eugene Jan 21 '13 at 08:07
Try it again. It works. ObjectOutputStream extends OutputStream so it is OutputStream – Evgeniy Dorofeev Jan 21 '13 at 08:19
I don't think so: "cannot find symbol symbol : method closeQuietly(java.io.ObjectOutput) location: class org.apache.commons.io.IOUtils" – Eugene Jan 21 '13 at 08:26
Maybe "s" is defined as ObjectOutput type causing this – Eugene Jan 21 '13 at 08:27
right, use ObjectOutputStream directly, ObjectOutput is an interface – Evgeniy Dorofeev Jan 21 '13 at 08:34
We have Java 8 but we can't use try with resources because of Sonar bug but IOUtils.closeQuietly(s); helped, thank you. – hipokito Feb 16 '17 at 21:43

score 1 · Answer 2 · answered Jan 21 '13 at 07:54

1

It means that s.close() will try to close underlying stream, but it may fail to do it. So to be sure you should close it on your own also. Try to add out.close() and see if warning disappears.

answered Jan 21 '13 at 07:54

partlov

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6
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Surely FindBugs would then highlight the `out = new ByteArrayOutputStream();` line? – Duncan Jones Jan 21 '13 at 07:54
It highlights line `s = new ObjectOutputStream(out);` because inside it is `out.close()`. It is just a warning that it can lead to errors. If that line wouldn't exist he will see no warnings. – partlov Jan 21 '13 at 07:58

FindBugs - "may fail to close stream" when using ObjectOutputStream

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