Sharing temporary data between disparate classes. Like a shared Map or something.

[Tim Cooke]

Good morning Ranchers,

I'm writing some tests and need to make some assertions based on values given during setup. Normally the setup and assertion hook methods live in the same class so is trivial to store data between them using local fields. However, in this case the setup and assertion methods live in different classes. For example:

public class MySetup {
    public void setupData(int pies) {
        dataStore.put("numPies", pies);
    }
}

public class MyAssertions {
    public void assertPies() {
        assertThat(dataStore.get("numPies"), is(7));
    }
}

Please put to one side the silliness of my example, I have simplified it from reality to the point where it looks ridiculous (doesn't even compile) but does demonstrate the key problem which is how to share the dataStore between classes.

I know that I could take a Map instance and wrap it up in a singleton, but I feel this is a problem that's likely already been solved so am looking for an 'off the shelf' solution. Perhaps Spring, or Guava, or Apache, or something else has a ready made solution?

Does anyone know of something like this?

Cheers, Tim

[Campbell Ritchie]

Tim Cooke wrote:. . . I could take a Map instance and wrap it up in a singleton, . . .

If you are sending the info only in one direction, what about a read‑only Map from Collections#unmodifiableMap().

[Tim Cooke]

How would the "sending" part work?

[Campbell Ritchie]

Create your Map in one location, with a getMap() method; you can then send data from that location but in a read‑only format. You can't send anything the other way with the same Map, obviously. If you are working in a small team, your ordinary Map would do nicely.

[Tim Cooke]

In the absence of anything better, I wrapped a HashMap in a singleton.

import java.util.HashMap;
import java.util.Map;

public enum SharedDataMap {
  DATA_MAP(new HashMap<>());

  private final Map<String, String> data;

  SharedDataMap(Map<String, String> data) {
    this.data = data;
  }

  public void put(String key, String val) {
    this.data.put(key, val);
  }

  public String get(String key) {
    return this.data.get(key);
  }

  public void clear() {
    this.data.clear();
  }
}

Suggestions for improvement are very welcome.