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Assuming, you have your Android app running in the Emulator on your local machine and server running on the same machine, then localhost won't refer to your server application. If you want to refer to the server application, then you should call the following IP address: 10.0.2.2 from the emulator running on the same machine as server.

When you call the server from the physical device, then find your IP address via ifconfig command (or ipconfig on Windows) in terminal, connect the mobile device to the same local network as server via WiFi and use appropriate IP address in your Android app.

EDIT

After your last edit, problem is more clear. You have two issues:

• setting the wrong host - it should be 10.0.2.2 instead of localhost
• calling request in the main thread - request should be called in a separate thread - e.g. with the AsyncTask (see official docs to find out how to use this class)