Question

The problem is that I have an old web service library that has a hashtable of global options which it combines with hashtable of request options. I cann’t influence request code, but I can set the global hashtable. And I was just curious if there is a simple way to implement an extention to Hashtable class that will perform a callback for some of the key to read some thread-local variable instead of its original value?

EDIT: I forgot to mention that I’m bound to JDK 1.4.2.

Answer 1

You can create a new class that derives from Hashtable and override the get() method.

Building on the code of twolfe18:

public class MyHashMap<K, V> extends HashMap<K, V> {
  TheadLocal special = new TheadLocal ();

  public MyHashMap<K, V>() {
    super();
  }

  public V get(K key) {
    if ("special".equals (key))
       return special.get ();

    return super.get(key);
  }
}

To set the value, use map.special.set(value). The value will be different per thread.