Java Concurrency Code Review

You are given a code snippet that is supposed to implement a simple in-memory cache that lazily loads values on the first request for a given key. The cache is accessed concurrently by many threads. Review the code, identify all concurrency problems, and then rewrite the class so it is thread-safe and efficient. Specifically:

1. Point out every race condition, data race, or violation of Java concurrency best-practices you can spot in the original implementation.
2. Rewrite the class so that:
   • at most one thread performs the expensive load operation for a given key;
   • no thread is blocked waiting for an already-completed load of the same key;
   • InterruptedException is handled correctly (never swallowed);
   • the implementation remains lock-free or fine-grained locked and scales under high contention.

Original code to review:

`java public class DataCache { private final Map<String, Data> cache = new HashMap<>();

public Data get(String key) throws InterruptedException {
    if (!cache.containsKey(key)) {
        Data data = loadExpensive(key);  // may throw InterruptedException
        cache.put(key, data);
    }
    return cache.get(key);
}

private Data loadExpensive(String key) throws InterruptedException {
    Thread.sleep(1000); // simulate slow I/O
    return new Data(key);
}

private static class Data {
    private final String key;
    Data(String key) { this.key = key; }
}

} `

Submit the list of issues you found and the complete corrected source code.