Printer Discovery from Android Device
Friday, 8 March 2013
This time I will show you how to discover Printers over a wifi network, to do this we need to use the jmDNS Java Library which is an implementation of Multi-Cats DNS, a network service discovery service.
First of all we need to create a Printer Object which is here:
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import java.net.InetAddress; public class Printer { private String name; private InetAddress address; public Printer(String name, InetAddress address) { this.name = name; this.address = address; } public String getName() { return name; } public void setName(String name) { this.name = name; } public InetAddress getAddress() { return address; } public void setAddress(InetAddress address) { this.address = address; } @Override public boolean equals(Object o) { if (o instanceof Printer) { Printer printer = (Printer) o; if (printer.name.equals(this.name)) return true; } return false; } } |
This class represents an instance of a Printer in the Local Network.
Then we need to implement the ServiceListener, here it is for you:
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package com.example.testandroid; import java.io.IOException; import java.net.InetAddress; import java.net.InetSocketAddress; import java.net.UnknownHostException; import java.util.ArrayList; import java.util.List; import javax.jmdns.JmDNS; import javax.jmdns.ServiceEvent; import javax.jmdns.ServiceListener; import android.content.Context; import android.net.wifi.WifiInfo; import android.net.wifi.WifiManager; import android.net.wifi.WifiManager.MulticastLock; import android.util.Log; /** * This class implements a network service listener to discover Printers over a * local wifi network, to aid this functionality this class implements the jmdns * Service listener which is an implementation of Multi-Cast DNS * * @author JPopoka */ public class PrinterDiscovery implements ServiceListener { private final String TAG = this.getClass().getName(); private Context context; /* Service type for printers */ private static final String SERVICE_TYPE = "_ipp._tcp.local."; /* List to store discovered printers */ private List printers; private Printer currentPrinter; /* Helper used for printer discovery */ private JmDNS jmdns; /* Wifi Lock to keep radio ON as needed */ private MulticastLock lock; /* Singleton Pattern shared instance methods ---------------------------- */ private static PrinterDiscovery printerDiscovery; private PrinterDiscovery(Context context) { this.context = context; printers = new ArrayList(); } /** * Singleton accessor to the instance * * @param context * @return instance - And instance of PrinterDiscovery */ public static PrinterDiscovery getInstance(Context context) { if (printerDiscovery == null) printerDiscovery = new PrinterDiscovery(context); return printerDiscovery; } /** * Starts the service to discover printers in the local network */ public void start() { new Thread(new Runnable() { @Override public void run() { startDiscovery(); } }).start(); } private void startDiscovery() { WifiManager wifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE); WifiInfo wifiInfo = wifiManager.getConnectionInfo(); int localIP = wifiInfo.getIpAddress(); if (localIP != 0) { byte[] byteaddr = new byte[] { (byte) (localIP & 0xff), (byte) (localIP >> 8 & 0xff), (byte) (localIP >> 16 & 0xff), (byte) (localIP >> 24 & 0xff) }; try { InetAddress addr = InetAddress.getByAddress(byteaddr); InetSocketAddress myServer = new InetSocketAddress(InetAddress.getByAddress(byteaddr), 9100); /* Adquire a wifi lock to keep radio ON */ lock = wifiManager.createMulticastLock("PRT LCK"); lock.setReferenceCounted(true); lock.acquire(); /* Create an instance of JmDNS and bind it to network */ jmdns = JmDNS.create(addr, "myJMDNS"); /* Bind this listener to the service */ jmdns.addServiceListener(SERVICE_TYPE, this); Log.d(TAG, "Listening to Printers"); } catch (UnknownHostException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } } } /* Stops the discovery service */ public synchronized void stop() { if (jmdns != null) { jmdns.unregisterAllServices(); try { jmdns.close(); } catch (IOException e) { e.printStackTrace(); } finally { jmdns = null; } } if (lock != null) { lock.release(); lock = null; } printerDiscovery = null; } public synchronized List getPrinters() { return printers; } public synchronized void selectPrinter(Printer printer) { this.currentPrinter = printer; } public synchronized Printer getCurrentPrinter() { return currentPrinter; } public synchronized Printer getPrinterByName(String name) { for (Printer printer : printers) { if (printer.getName().equals(name)) return printer; } return null; } /* Service Listener methods --------------------------------------------- */ // @SuppressWarnings("deprecation") @Override public void serviceResolved(ServiceEvent ev) { Log.d(TAG, "service resolved: " + ev.getInfo().getName() + ", port: " + ev.getInfo().getPort() + " address: " + ev.getInfo().getInetAddress()); Printer printer = new Printer(ev.getInfo().getName(), ev.getInfo().getInetAddress()); printers.add(printer); } @SuppressWarnings("deprecation") @Override public void serviceRemoved(ServiceEvent ev) { Log.d(TAG, "service removed: " + ev.getName()); Printer printer = new Printer(ev.getInfo().getName(), ev.getInfo().getInetAddress()); printers.remove(printer); } @Override public void serviceAdded(ServiceEvent ev) { Log.d(TAG, "service added, name: " + ev.getName() + ", type: " + ev.getType()); jmdns.requestServiceInfo(ev.getType(), ev.getName(), 1); } } |
We instantiate it on our main activity
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. . . public class MainActivity extends Activity { final String TAG = ""; PrinterDiscovery pd; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); pd = PrinterDiscovery.getInstance(getApplicationContext()); } . . . |
And finally we start it and stop it onResume and onPause respectively:
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. . . @Override protected void onResume() { super.onResume(); Log.d(TAG, "Resume"); pd.start(); } @Override protected void onPause() { super.onPause(); pd.stop(); Log.d(TAG, "Paused"); } . . . |
We should see on the Log something like this:
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Listening to Printers service added, name: HP LaserJet 100, type: _ipp._tcp.local service resolved, name: HP LaserJet 100, port: 631 address: /192.168.1.57 |
Remember to add this permissions in your manifest:
<uses-permission android:name=”android.permission.INTERNET”/>
<uses-permission android:name=”android.permission.ACCESS_WIFI_STATE” />
<uses-permission android:name=”android.permission.CHANGE_WIFI_MULTICAST_STATE” />