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Performing HTTP operations with Android. This article describes how to access web resources via HTTP in Android. It is based on Eclipse 4.4, Java 1.6 and Android 5.0 (Lollipop).

1. Overview of HTTP access on Android

1.1. Available official API’s

Android contains the standard Java network java.net package which can be used to access network resources. The base class for HTTP network access in the java.net package is the HttpURLConnection class.

Android also contains the Apache HttpClient library but it is not recommended anymore to use it, as Google is focusing their efforts on improving the HttpURLConnection implementation.

1.2. Required permissions

To access the Internet your application requires the android.permission.INTERNET permission.

To check the network state your application requires the android.permission.ACCESS_NETWORK_STATE permission.

1.3. Open source libraries

Performing network operations on Android can be cumbersome. You have to open and close a connections, enable caches and ensure to perform the network operation in a background thread.

To simplify these operations several popular Open Source libraries are available. The most popular ones are the following:

  • Volley

  • OkHttp

2. Good practices for network access under Android

Within an Android application you should avoid performing long running operations on the user interface thread. This includes file and network access.

As of Android 3.0 (Honeycomb) the system is configured to crash with a NetworkOnMainThreadException exception, if network is accessed in the user interface thread.

A typical setup for performing network access in a productive Android application is using a service. While it is possible to do network access from an activity or a fragment, using a service typical leads to a better overall design because you code in the activity becomes simpler.

For testing you can allow network access in the main thread via the following snippet. at the beginning of your onCreate() method of your activity.

StrictMode.ThreadPolicy policy = new StrictMode.
ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);

Unresolved directive in 001_article.adoc - include::../JavaNetworking/010_overview.adoc[] == Check the network availability

Obviously the network on an Android device is not always available. You can check the network is currently available via the following code.

public boolean isNetworkAvailable() {
    ConnectivityManager cm = (ConnectivityManager)
            getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo networkInfo = cm.getActiveNetworkInfo();
    // if no network is available networkInfo will be null
    // otherwise check if we are connected
    if (networkInfo != null && networkInfo.isConnected()) {
        return true;
    }
    return false;
}

This requires the ACCESS_NETWORK_STATE permission.

3. Web Sockets

Web Sockets are a standard based on HTTP for asynchronous message-based communication between a client and a server. To start a web socket communication, you create a HTTP GET request with a special HTTP headers. If the server accepts this request, the client and the server can send each other messages.

Messages can be text or binary data and should be relatively small, as the web socket protocol is intended to be used with small payloads in the data.

It is good practice to use JSON as data format for the messages.

You find a Java library for both the server and the client under http://java-websocket.org/ .

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5.1. Android Resources

Introduction to Android Development

Android Location API and Google Maps

Android Homepage

Crest Framework to access rest services, works also on Android

Apache HttpClient

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