Android应用程序开发和Web服务器交互

Question

I am just learning about Android Development so excuse me if this is a bit off in nature. I am wanting to make an app that interacts with a Database from my website, in a sense the two things will be one feeding the other. So with that. I am trying to figure out whats the best way to interact with my server. I don't want an app thats an app in a browser like environment I want to dev a full app that works independently of the site only sharing the DB and like features. So what would be my best approach?

Is building the app so it can post/get to php files on the server interacting basically through JSON/XML my best and or safest bet or is there a better approach that connects the App to the servers Database that doesn't require me to open the database to any ip that makes a request.

Just looking for opinions and suggestions here. I figure everyone who's going to see this is familiar with Android development and best practices where as I could and have surfed blogs and all else but the opinion seems to be 50/50 as to which is best.

Answer 1

I'm sure there are libraries out there for Android that help you with HTTP Get and Post, however, if you really want to understand what is going there are just a couple of classes you have to understand in order to make the necessary classes yourself.

First, get to know HttpClient, HTTPGet, HTTPPost, and HTTPResponse. Some of the later versions of Android have some nice other classes as well, but those four is pretty much all you need to get started.

You need to do something like this:

HttpClient client = new DefaultHttpClient();
HttpGet request = new HttpGet("http://www.myurl.com/api_name");
HttpResponse response = client.execute(request);

If you debug this (with a real URL of course), you'll notice that your app kind of freezes during client.execute(). This is the point at which the request has actually fired and the app is waiting for a response. Once you actually get the response, it isn't very difficult to get the data out of it.

Once you understand this, you'll want to get to know AsyncTask, which is endlessly useful for performing background tasks. You can find the documentation here: http://developer.android.com/reference/android/os/AsyncTask.html There is a great example of how to use this right at the top.

Using these two concepts together you can perform asynchronous HTTP requests. Basically, put your actual HTTP execute code in doInBackground of your AsyncTask. At the end of the doInBackground return your response, and then do what you want with your data in the AsyncTask's onPostExecute.

Answer 2

We've found that providing a proper RESTful web API that hits the database on the backend in whatever language you choose (be it PHP, RoR, whatever) provides a useful interface for any number of uses (your own website, mobile apps, etc).

Then it's a matter of your Android app interacting with the RESTful API, which is simply HTTP requests. Those can be encapsulated in helper classes to make them straightforward as well.

Answer 3

Based on my experience, the best framework for doing RESTFul things with Android is: Spring Android

From a client perspective, it provides all the tools needed to access secure RESTFul services. Since it is Spring, it provides nice abstractions over most of the boiler plate http code. As an example, it provides a clean way to perform a GET that returns json, and then serialize that to a POJO.

As an example:

RestTemplate restTemplate = new RestTemplate();

// Add Jackson JSON Message Converter to Template
restTemplate.setMessageConverters(
    new ArrayList<HttpMessageConverter<?>>() {
        {              
            add(new MappingJacksonHttpMessageConverter());
        }
    }
);  

// Simple Conversion - pojo is now populated
MyPojo pojo = restTemplate.getForObject(url, MyPojo.class);

Answer 4

The approach you mention in the question: PHP on the server and JSON for requests/responses, does work. But getting it perfect can be tricky.

I found it helpful to have small request/reponse classes for each call on the Android side, like SaveNoteToServerRequest, SaveNoteToServerResponse classes which are just plain java objects with whatever fields are needed for the request/response. Then you can use a library like GSON to convert the request object to JSON and convert the http response from JSON to the response object.

On the PHP side you can create a small class for the response object, then json_encode at the end.

That way you're not directly manipulating JSON objects, just using your own plain java objects or php classes most of the time.

Hope that helps.