Using Spring Android
---------------------

- Using Spring in Android applications usually involves
  and Android application using Spring to work with 
  RESTful resources.

- There's an article about the topic at:

http://spring.io/guides/gs/consuming-rest-android


Spring RESTful clients
----------------------

- Spring itself (not just for Android) provides a
  RestTemplate type that simplifies acting as a
  RESTful client.

- The RestTemplate type defines methods to perform
  the classic REST operations, including:

   // GETs a Java object from a RESTful URL
    <T> T getForObject(String url, Class<T> objectType)

    // POSTs a Java object to a RESTful URL and
    // returns the Location header (the new object's URL)
    URI postForLocation(String url, Object obj)

   // PUTs a Java object to a RESTful URL
   void put (String url, Object obj)

    // delete a RESTful representation
   void delete (String url);

- The template methods that work with objects require
  at least one MessageConverter that know how to convert
  a RESTful representation (e.g. JSON) to/from Java objects.
  For JSON, you can use MappingJackson2HttpMessageConverter.
  For XML, Jaxb2RootElementHttpMessageConverter.

  After creating the RestTemplate, you can add message
  converter(s):

    RestTemplate restTemplate = new RestTemplate();
    restTemplate.getMessageConverters().add(
      new MappingJackson2HttpMessageConverter());	

- After configuring the MessageConverter, you can
  work with RESTful resources:

  MyClass g = restTemplate.getForObject(url, MyClass.class);


Configuring an Android Project For Spring-Android
-------------------------------------------------

- If you are using the Android Development Kit, you
  can create a normal Android project, and then add the
  Spring-Android JARs to the project's "libs" folder.
  At minimum, for RestTemplate and JSON, you need these
  JARs:

    jackson-annotations-x.x.x.jar  // x.x.x is version
    jackson-core-x.x.x.jar
    jackson-databind-x.x.x.jar
    spring-android-auth-y.y.y.RELEASE.jar
    spring-android-core-y.y.y.RELEASE.jar
    spring-android-rest-template-y.y.y.RELEASE.jar


Coding an Android Rest Application
-----------------------------------

- Then you can create an Android layout and Activity
  in the normal way. Then determine what will trigger
  your app's REST requests - for example, you might
  use a button click:

  myButton = (Button) findViewById(R.id.button1);
  myButton.setOnClickListener(new View.OnClickListener()
  {
     public void onClick(View v)
     {
         // code to initiate REST request goes here
         new MyAsyncTask().execute(); // see next
     }
  });
  
  
- For best responsiveness, you should use an asynchronous
  technique to make the request. Android provides the
  AsyncTask type that you can subclass and in which you
  can code your methods to work with RESTful resources.

   private class MyAsyncTask extends AsyncTask<Void, Void, MyClass>
   {
      . . .
   }

   The three parameterized types to AsyncTask are parameters,
   progress and result - in this example, we will only
   work with the result. We type this generic class to 
   MyClass so the method in our subclass can work with MyClass
   objects.

- The AsyncTask actually runs through four steps, but we will
  only use two - doInBackground(), in which we can initiate
  our asynchronous request and onPostExecute() which Android calls
  when the request is complete. Here's what the code to get
  a RESTful resource might look like (exception handling omitted):

   private class MyAsyncTask extends AsyncTask<Void, Void, MyClass>
   {
    // start the async request
    protected MyClass doInBackground(Void... params)
    {
     final String url = ... // URL of JSON RESTful resouce

     RestTemplate restTemplate = new RestTemplate();
     restTemplate.getMessageConverters().add(new 
         MappingJackson2HttpMessageConverter());

      MyClass g = restTemplate.getForObject(url, MyClass.class);
      return g;

     }

      // display results of request
      protected void onPostExecute(MyClass g)
      {
          Toast.makeText(MainActivity.this,
             g.toString(), Toast.LENGTH_SHORT)
                    .show();		
       }
   }