java - Cache Invalidation while Getting from WeakHashMap

Question

I cache database connection objects via WeakHashMap as like:

    Connection conn;
    if (connectionCache.get(jdbc.getConnectionURL()) == null) {
        conn = DriverManager.getConnection(jdbc.getConnectionURL(), jdbc.getUsername(), jdbc.getPassword());
        connectionCache.put(jdbc.getConnectionURL(), conn);
    } else {
        conn = connectionCache.get(jdbc.getConnectionURL());
    }

Is it possible:

If statement is checked and seen that there is already an object at cache and before running else statement cache is invalidated?

Answer 1

从技术上讲，它是但它非常罕见。解决方案非常简单：

如果你想使用在 if 中检查的值，它不为 null，你可以在 if 中分配它，这样你就不需要在 else 中再次从缓存中检索它：

    Connection conn;
    if ((conn = connectionCache.get(jdbc.getConnectionURL())) == null) {
        conn = DriverManager.getConnection(jdbc.getConnectionURL(), jdbc.getUsername(), jdbc.getPassword());
        connectionCache.put(jdbc.getConnectionURL(), conn);
    }