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how to search for network in android studio while using socket?

public void connect() {
final String msg = "";
Thread thread = new Thread(new Runnable() {
#Override
public void run() {
try {
s = new Socket("192.168.1.3", 1337);
textView.setText("Connection acquired");
out = s.getOutputStream();
output = new PrintWriter(out);
output.println(msg);
textView.setText("message sent : " + msg.length());
output.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
});
thread.start();
}
I am using the above code to connect to desired IP [192.168.1.3]... I have created another program at the other end... The problem is that the IP sometimes changes to 192.168.1.4 or 192.168.1.6... and when I use another network it changes to 192.168.43.2... now due to this I have to go every time into the code and change it manually....
Is there any function or any other thing that might search for IPs available then check if desired port exists and then connect... Thanks in advance

That's why DNS names exist. If you use an IP address, you have to use that exact address. If you use DNS, you do a name->IP lookup. Get a dynamic DNS provider and use that to give your server a name.
You really do not want to start port scanning to find open ports. You will be treated as an attacker and kicked off the network, because you really would be doing something attackers do.

Mongo client {Mongo-Java-driver} creation hangs duration . No exception thrown

I have a cron-job running at a Linux machine running after every 5 minutes. The job executes a Java class.
private MongoClient createConnection(int retry,List<ServerAddress> host){
try {
System.out.println("Retrying----------"+retry);
MongoClient client = new MongoClient(host, MongoClientOptions.builder()
.connectionsPerHost(10)
.threadsAllowedToBlockForConnectionMultiplier(5)
.connectTimeout(5000).writeConcern(WriteConcern.NORMAL).build());
client.getDB("admin").command("ping").throwOnError();
retry = 0;
return client;
} catch (Exception e) {
retry++;
if (retry < retryLimit) {
createConnection(retry,host);
} else {
System.out.println("Connection could not be established to host-"+host);
}
return null;
}
}
retry is the integer value denoting how many times client creation can be tried in case host is unreachable.
The host list that i am passing is -
public static List<ServerAddress> HOST_SCRIPT = new ArrayList<ServerAddress>() {
private static final long serialVersionUID = 1L;
{
try {
add(new ServerAddress("PrimaryHost23", 27017));
} catch (UnknownHostException e) {
e.printStackTrace();
}
}
};
Code is Stuck when i MongoClient is being created. It does not happen always. Code works fine and NEVER hangs when i run on my local machine. There is no exception thrown.
I recently upgraded Linux machine OS (from CentOS 5 to CentOS 6). Can this be responsible for this because this script was working fine earlier.
Please help.
Regards,
Vibhav

The thing what you can do is you can throw mongo exception try out that of mongo client is stuck you will get to know try out this https://api.mongodb.org/java/2.6/com/mongodb/MongoException.html

Yes of course, actually i was creating crawler in java which fetch all the links of any particular website and validate the css and html structure Using the Jsoup and jcabi api but when i used to store links to the database it was not throwing any exception and even not storing the data also. so i did this
catch (MongoException e){
System.err.print(e.getClass().getName()+": "+e.getMessage());
}

Have you checked the compatibility like of jar that you have uploaded for your project like before it was like Mongo mongo = new Mongo(host,port); but That is deprecated. Try to check that and even your MongoDb jar.

Client-Server connects while being on the same computer but not while being run on different ones

I'm trying to build a basic client-server application.
When I run both the server and the client on the same computer both manage to connect without a hitch but if I try to do so from different computers (desktop and laptop) the connection doesn't get though. The server isn't even aware that someone tried to connect to it while the client timeouts after a while. At first I assumed that it's a firewall problem but disabling the firewall completely on the server PC did not help. Tried changing ports and checked on multiple computers. Any ideas what could cause this?
I control both the server and the client and can change the code of both if necessary. The server always runs on the same PC and I'm connecting to it directly using hardcoded IP address.
This is the code of the client sending random int to the server.
public static void main(String[] args) {
Socket s = new Socket();
try {
s.connect(new InetSocketAddress("123.45.67.891", 8084), 5000);
s.getOutputStream().write(42);
s.close();
} catch (IOException e) {
e.printStackTrace();
return;
}
}
The server is slightly more complicated but considering the fact that they manage to connect while being run from the same PC I assume that the problem isn't with it.
edit: Server code (Thread per client. There shouldn't be too many of those)
public void run() {
try {
serverSocket = new ServerSocket(listenPort); //integer
} catch (IOException e) { ... }
while (shouldRun) {
try {
Socket clientSocket = serverSocket.accept(); // Blocked here while trying to connect from remote computer
//Never gets here
ConnectionHandler newConnection = connectionHandlerCreator.create(clientSocket);
connectionHandlers.add(newConnection);
newConnection.initialize();
new Thread(newConnection).start();
} catch (IOException e) { ... }
}
}
Initialize consists of the following (which latter used for I/O).
in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
out = new PrintWriter(clientSocket.getOutputStream(), true);

The problem is probably on your server side though: you have to make it respond to all ip's not just local one, by using the constructor:
ServerSocket(int port)
it will default accepting connections on any addresses which is not the case if you specified an IP

Java derby database server won't start anymore

I inherited some source code that uses a derby database but starting the server doesn't work anymore.
public void startDatabase(){
try {
Class.forName("org.apache.derby.jdbc.ClientDriver");
System.setProperty("derby.system.home", "D:\\runtime-my.product\\log");
NetworkServerControl nsc = new NetworkServerControl(InetAddress.getByName("localhost"), 1527)
nsc.start(null);
nsc.ping();
catch (Exception e){
e.printStackTrace();
}
}
When nsc.ping() is exectued, the following exception is thrown:
Exception: java.lang.Exception: DRDA_NoIO.S:Could not connect to Derby Network Server on host 127.0.0.1, port 1527: Connection refused: connect
Is there anything obvious missing or wrong with those lines of codes?

Check whether the server is started. You need to start the server explicitly. or via
setting the system property derby.drda.startNetworkServer=true.

It takes a while from the NetworkServerControl constructor returns, before the socket is ready for connections. On my machine about 50 ms. I changed your example like so:
NetworkServerControl nsc = new NetworkServerControl(InetAddress.getByName("localhost"), 1527);
nsc.start(null);
for (int i = 0; i < 10; ++i) {
try {
System.out.println("Attempting to ping...");
nsc.ping();
break;
} catch (Exception e) {
System.out.println(e.getMessage());
}
Thread.sleep(10);
}
It succeeded on the 5. attempt...

MongoDB: check connection to DB

I'm looking for best way to check connection to Mongo DB.
Situation: client makes request (api) to server. And server returns status of all databases.
What the best way to do it?

I use this:
Builder o = MongoClientOptions.builder().connectTimeout(3000);
MongoClient mongo = new MongoClient(new ServerAddress("192.168.0.1", 3001), o.build());
try {
mongo.getAddress();
} catch (Exception e) {
System.out.println("Mongo is down");
mongo.close();
return;
}

In Java MongoDriver 3.3.0 use ServerMonitorListener to determine whether server is up and connected or not.
Here is the example code,
public class ServerConnection implements ServerMonitorListener {
private MongoClient client;
public ServerConnection(){
try {
MongoClientOptions clientOptions = new MongoClientOptions.Builder()
.addServerMonitorListener(this)
.build();
client = new MongoClient(new ServerAddress("localhost", 27017), clientOptions);
} catch (Exception ex) {
}
}
#Override
public void serverHearbeatStarted(ServerHeartbeatStartedEvent serverHeartbeatStartedEvent) {
// Ping Started
}
#Override
public void serverHeartbeatSucceeded(ServerHeartbeatSucceededEvent serverHeartbeatSucceededEvent) {
// Ping Succeed, Connected to server
}
#Override
public void serverHeartbeatFailed(ServerHeartbeatFailedEvent serverHeartbeatFailedEvent) {
// Ping failed, server down or connection lost
}
}

The ping command is a no-op used to test whether a server is responding to commands. This command will return immediately even if the server is write-locked:
try{
DBObject ping = new BasicDBObject("ping", "1");
mongoTemplate.getDb().getMongo().getDB("DATABASE NAME"").command(ping);
} catch (Exception exp){
// MongoDb is down..
}

Use MongoClient for Java, all the info you need is here...
http://docs.mongodb.org/ecosystem/tutorial/getting-started-with-java-driver/

If I understand your question correctly you want to get state returned via a web service call. You can write a function that invokes db.serverStatus() and have it return the data. Check out the documentation here:
Monitoring for MongoDB