potential resource leak (unassigned Closeable) with a HashMap

Question

I have one static HashMap for my entire system which contains some object's references; let's call it myHash. The objects are only instantiated once I needed them such as

private static HashMap<String, lucene.store.Directory> directories;

public static Object getFoo(String key) {
    if (directories == null) {
        directories = new HashMap<String, Directory>();
    }
    if (directories.get(key) == null) {
        directories.put(key, new RAMDirectory());
    }
    return directories.get(key); // warning
}

Now, Eclipse is telling me a warning in the return statement:

Potential resource leak: '<unassigned Closeable value>' may not be closed at this location

Why is eclipse telling me that?

And what is `whatever`? If you could turn this into a short but *complete* example demonstrating the problem, it would be a lot easier to help you. — Jon Skeet, May 21 '14 at 09:31

sp00m · Accepted Answer · 2014-05-21T09:51:01.820

Directory is a Closeable that is not closed in the same method it is instantiated in, Eclipse warns you this could create potential resource leaks if not closed somewhere else. In other words, a Closeable instance should always be closed somewhere, whatever error could have been thrown.

Here is the usual way to use a Closeable in Java 7+:

try (Directory dir = new RAMDirectory()) {
    // use dir here, it will be automatically closed at the end of this block.
}
// exception catching omitted

In Java 6-:

Directory dir = null;
try {
    dir = new RAMDirectory();
    // use dir here, it will be automatically closed in the finally block.
} finally {
    if (dir != null) {
        dir.close(); // exception catching omitted
    }
}

potential resource leak (unassigned Closeable) with a HashMap

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