Add string representation for all POJOs

[dexX7]

Let me quickly describe what issue I faced yesterday:

I wanted to dump some intermediate results, in particular of listUnspent, which returns a List of UnspentOutputs.

The change was basically:

@@ -166,2 +166,3 @@ class SendToOwnersReorgSpec extends BaseReorgSpec {
         when: "creating a third STO transaction"
+        println listUnspent(0, 999999)
         def thirdTxid = omniSendSTO(actorAddress, tokenID, 50.divisible)

However, the result:

[com.msgilligan.bitcoinj.json.pojo.UnspentOutput@3a13055a, ...]

It would be nice, if the UnspentOutput (and others) would be converted to something readable, such as:

[{"txid":"hex","vout":n,"address":"1base58",...}, ...]

The Groovy @ToString() class annotation may be useful?

[msgilligan]

If the POJOs were POGOs we could use the Groovy @toString annotation, but I think we want to keep the core functionality in straight Java.

I've heard good things about Project Lombok that has similar features (including a @toString annotation) for straight Java, but at the expense of additional compile-time and IDE tooling. I'm leaning against using it for this project, but would like to try it out on another project sometime. (There's also a prototype implementation of using Groovy annotations to make POJOs, see GROOVY-7492.)

I think there are two approaches worth considering:

1. Write toString() methods by hand.

2. Use the Jackson ObjectMapper to convert to JSON String:

   println mapper.writeValueAsString(listUnspent(0, 999999))
   

We may be able to add some Groovy code to tests to make (2) more easily accessible or perhaps even automatic.