support basic yaml parsing

[GoogleCodeExporter]

other libraries that support yaml are extremely bad at the things you guys are 
good at. 

for example, you guys are very good at handling injecting data into classes 
with custom constructors, coercing generic types, intuitive serializers, 
deserializers.

I'm not necessarily asking for advanced yaml, with munging, etc.  mainly a 
gson-like deserializer for yaml which is as clean as you current code is, and 
clearly benefits from all the core stuff in gson that isn't json dependent.

Here's an example of what we otherwise have to deal with:

   class SelectiveConstructor extends Constructor {
      public SelectiveConstructor() {
         // define a custom way to create a mapping node
         yamlClassConstructors.put(NodeId.mapping, new MyPersistentObjectConstruct());
      }

      class MyPersistentObjectConstruct extends Constructor.ConstructMapping {
         @Override
         protected Object constructJavaBean2ndStep(MappingNode node, Object object) {
            Class type = node.getType();
            if (type.equals(MyPersistentObject.class)) {
               // create a map
               Map map = constructMapping(node);
               String id = (String) map.get("id");
               return new MyPersistentObject(id, 17);
            } else {
               // create JavaBean
               return super.constructJavaBean2ndStep(node, object);
            }
         }
      }
   }

   public void testConstructor() throws IOException {
      Yaml yaml = new Yaml(new SelectiveConstructor());
      List<?> data = (List<?>) yaml.load("- 1\n- 2\n- !!examples.MyPersistentObject {amount: 222, id: persistent}");
      // System.out.println(data);
      assertEquals(3, data.size());
      MyPersistentObject myObject = (MyPersistentObject) data.get(2);
      assertEquals(17, myObject.getAmount());
      assertEquals("persistent", myObject.getId());
   }

Original issue reported on code.google.com by [email protected] on 15 May 2011 at 4:08

[prosavage]

Will do this soon :)