Question

I made some tests (using Windows 7, Eclipse Juno 4.2.1 and Java 7 SE) and found that if a method did not explicitly return in the catch-block and if the object was declared outside the try/catch, then no “resource leak” warning was signaled.

Does not generate “resource leak”:

    public void extISImReturnNoWarning() {
    InputStream is = null;
    try {
        is = new FileInputStream("A");
        is.available();
    } catch (IOException e) {
    }
}

Small changes in the code generate “resource leaks”:

public void locISImReturnHasWarning() {
    try {
        InputStream is = new FileInputStream("A");
        is.available();
    } catch (IOException e) {
    }
}

public void extISExReturnHasWarning() {
    InputStream is = null;
    try {
        is = new FileInputStream("A");
        is.available();
    } catch (IOException e) {
        return;
    }
}

All methods seems functionally identical – so what can the explanation be? If this is a bug, is this an Eclipse or Java issue?

Answer 1

After some research, I’ve come to the conclusion that this is an Eclipse bug. I’ve tested it in the latest build I’ve found on Eclipse Download site (Kepler M3), but the issue persists. I’ve also found 5-6 bug reports on similar issues reported the last 30 days in the Eclipse project. During the research I also found another peculiar behavior:

    public void makeConnection() throws SQLException {
    Connection connection = null;
    try {
        connection = DriverManager.getConnection("localhost");
        for (int i = 0; i < 1; i++)
            if (i < 1)
                throw new SQLException("Foo");
        connection.commit();
    } finally {
        close(connection);
    }
}

public void close(Connection c) {
}

This code will generate a resource leak warning. However, by removing one of these

• the call to close(connection)
• the for-loop

..the resource leak warning will disappear. Strangely enough – no resource leak will be reported in a vanilla case, where you simply create a connection and do not close it.

All in all, I think the resource leak detection in Eclipse Juno might be a little bug-prone for the time being. Maybe it’s for the best to ignore resource leaks in Eclipse right now, and wait for Kepler.

Update dec 2014 : Currently running Eclipse Luna, and the issue persists…