We Keep Coding

Caused by: java.net.UnknownHostException: www.btechldap.com

I am trying to access LDAP Server through Java code as I have founded a free hosted server on the internet and want to test the reading mechanism via LDAP. But when I access it I get the captioned exception.
I have surfed on the internet and found that the LDAP URL Format shall be as per the correct practice and standard. I fixed that too, but nothing worked.
I dont know where I have done a mistake.
The complete stack trace is provided below:
Exception
Rdentry example failed.
javax.naming.CommunicationException: www.btechldap.com:1389 [Root exception is java.net.UnknownHostException: www.btechldap.com]
at com.sun.jndi.ldap.Connection.<init>(Unknown Source)
at com.sun.jndi.ldap.LdapClient.<init>(Unknown Source)
at com.sun.jndi.ldap.LdapClient.getInstance(Unknown Source)
at com.sun.jndi.ldap.LdapCtx.connect(Unknown Source)
at com.sun.jndi.ldap.LdapCtx.<init>(Unknown Source)
at com.sun.jndi.ldap.LdapCtxFactory.getUsingURL(Unknown Source)
at com.sun.jndi.ldap.LdapCtxFactory.getUsingURLs(Unknown Source)
at com.sun.jndi.ldap.LdapCtxFactory.getLdapCtxInstance(Unknown Source)
at com.sun.jndi.ldap.LdapCtxFactory.getInitialContext(Unknown Source)
at javax.naming.spi.NamingManager.getInitialContext(Unknown Source)
at javax.naming.InitialContext.getDefaultInitCtx(Unknown Source)
at javax.naming.InitialContext.init(Unknown Source)
at javax.naming.InitialContext.<init>(Unknown Source)
at javax.naming.directory.InitialDirContext.<init>(Unknown Source)
at LDAPAccess.main(LDAPAccess.java:33)
Caused by: java.net.UnknownHostException: www.btechldap.com
at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.SocksSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at java.net.Socket.<init>(Unknown Source)
at java.net.Socket.<init>(Unknown Source)
at com.sun.jndi.ldap.Connection.createSocket(Unknown Source)
... 15 more
CODE
import java.util.Hashtable;
import javax.naming.Context;
import javax.naming.NamingEnumeration;
import javax.naming.NamingException;
import javax.naming.directory.Attribute;
import javax.naming.directory.Attributes;
import javax.naming.directory.DirContext;
import javax.naming.directory.InitialDirContext;
public class LDAPAccess {
public static void main(String[] args) {
Hashtable env = new Hashtable(5, 0.75f);
/*
* Specify the initial context implementation to use.
* This could also be set by using the -D option to the java program.
* For example,
* java -Djava.naming.factory.initial=com.sun.jndi.ldap.LdapCtxFactory \
* Rdentry
*/
env.put(Context.INITIAL_CONTEXT_FACTORY, "com.sun.jndi.ldap.LdapCtxFactory");
/* Specify host and port to use for directory service */
env.put(Context.PROVIDER_URL, "ldap://www.btechldap.com:1389/dc=btechsample,dc=com");
env.put(Context.SECURITY_AUTHENTICATION, "simple");
env.put(Context.SECURITY_CREDENTIALS, "btechpass");
try {
/* get a handle to an Initial DirContext */
DirContext ctx = new InitialDirContext(env);
/* Read Babs' entry */
Attributes attrs = ctx.getAttributes("uid");
if (attrs == null) {
System.out.println("uid" + "has no attributes");
} else {
/* print each attribute */
for (NamingEnumeration ae = attrs.getAll();
ae.hasMoreElements();) {
Attribute attr = (Attribute)ae.next();
String attrId = attr.getID();
/* print each value */
for (NamingEnumeration vals = attr.getAll();
vals.hasMoreElements();
System.out.println(attrId + ": " + vals.nextElement()))
;
}
}
} catch (NamingException e) {
System.err.println("Rdentry example failed.");
e.printStackTrace();
}
}
}
I am new to LDAP, Please help!

The code is specifying the credentials (password) but missing the principal (i.e. the user to authenticate as).
Just add the following line:
env.put(Context.SECURITY_PRINCIPAL, "cn=readonlybind,ou=admins,dc=btechsample,dc=com");

Amazon RDS Connection Error

I have trying to connect to Amazon RDS and were able to connect it once though I am unable to connect it again. I have checked my username, password, database name, server, etc. and they are all correct. I have all the required files included before the compilation.
I have attached my code below:
import java.io.File;
import java.net.URL;
import java.sql.*;
import java.util.*;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.InputSource;
import java.net.URL;
import java.sql.*;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.InputSource;
public class test_url {
#SuppressWarnings("null")
public static void main(String[] args){
String url = "jdbc:mysql://newtes.ctt52jgw7nwb6.eu-west-1.rds.amazonaws.com:3306/";
String userName = "amankijawani";
String password = "vegasishere";
String dbName = "newtesDB";
String driver = "com.mysql.jdbc.Driver";
System.out.println("Connecting database...");
try {
Class.forName("com.mysql.jdbc.Driver");
Connection connection = DriverManager.getConnection(url + dbName, userName, password);
System.out.println("Database connected!");
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
ERROR
Connecting database...
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:988)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:341)
at com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2251)
at com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2284)
at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2083)
at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:806)
at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:47)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:404)
at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:410)
at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:328)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at test_url.main(test_url.java:44)
Caused by: java.net.ConnectException: Connection timed out: connect
at java.net.DualStackPlainSocketImpl.connect0(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.SocksSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:211)
at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:300)
... 15 more

RMI server ClassNotFoundException when client makes call

I am trying to make a simple RMI execution engine to run on my local machine so that other java programs can easily run code on a second processor. (In the future this will be expanded to allow more processors).
The server starts up just fine, and the client appears to locate the registry ok, but when it tries to call the execution engine (and passes it a parameter) it causes a ClassNotFoundException.
I recognize that this is similar to many other questions on stack overflow, but as far as I can tell, all the other ones have to do with the client not being able to download the server's classes rather than the server not being able to download the client's classes.
Here is my code (copied almost exactly from this sample code):
RMIServer eclipse project
ComputeEngine Interface:
package interfaces;
import java.io.Serializable;
import java.rmi.Remote;
import java.rmi.RemoteException;
public interface ComputeEngine_IF extends Remote {
/**
* #param task The task object specifying the computation to be performed
* #return
* #throws RemoteException
*/
<T extends Serializable> T compute(TaskWithoutInput<T> task) throws RemoteException;
}
TaskWithoutInput interface:
package interfaces;
import java.io.Serializable;
public interface TaskWithoutInput<T> extends Serializable {
public T compute();
}
ComputeEngine Class:
package server;
import interfaces.ComputeEngine_IF;
import interfaces.TaskWithoutInput;
import java.io.Serializable;
import java.rmi.RemoteException;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
import java.rmi.server.UnicastRemoteObject;
public class ComputeEngine implements ComputeEngine_IF{
public ComputeEngine() {
super();
}
#Override
public <T extends Serializable> T compute(TaskWithoutInput<T> task) throws RemoteException {
return task.compute();
}
public static void main(String[] args) {
if(System.getSecurityManager() == null) {
System.setSecurityManager(new SecurityManager());
}
try {
String name = "Compute";
ComputeEngine_IF engine = new ComputeEngine();
ComputeEngine_IF stub = (ComputeEngine_IF) UnicastRemoteObject.exportObject(engine, 0);
Registry registry = LocateRegistry.createRegistry(1099);
registry.rebind(name, stub);
System.out.println("Registry bound!");
}
catch (Exception e) {
System.err.println("ComputeEngine exception:");
e.printStackTrace();
}
}
}
RMIClient eclipse project
GetAnswerTask class
package client;
import interfaces.TaskWithoutInput;
public class GetAnswerTask implements TaskWithoutInput<Integer> {
private static final long serialVersionUID = 1L;
#Override
public Integer compute() {
return Integer.valueOf(42);
}
}
Client class
package client;
import interfaces.ComputeEngine_IF;
import interfaces.TaskWithoutInput;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
public class RmiClientExample {
public static void main(String args[]) {
if(System.getSecurityManager() == null) {
System.setSecurityManager(new SecurityManager());
}
try {
String name = "Compute";
Registry registry = LocateRegistry.getRegistry("localhost");
ComputeEngine_IF comp = (ComputeEngine_IF) registry.lookup(name);
TaskWithoutInput<Integer> getAnswer = new GetAnswerTask();
Integer answer = comp.compute(getAnswer);
System.out.println("Answer: " + answer);
}
catch (Exception e) {
System.err.println("RmiClientExample exception:");
e.printStackTrace();
}
}
}
Both projects contain an identical security policy file (in RMIServer it is called server.policy and in RMIClient it is called client.policy)
grant {
permission java.security.AllPermission;
};
I will, of course, restrict the permissions more once I get this working.
Building/Running
Since the code is pretty close to something I copied out of an example, my guess is that the code is right, or at least close, but that my mistake is in compiling/running the code. The example wasn't written for eclipse, so I don't have exact instructions.
The first thing I did was use eclipse's jar export wizard to jar the interface package into Interfaces.jar which I just placed in my RMIServer folder.
Then I run ComputeEngine with the following defines:
-Djava.rmi.server.codebase=file:/c:/Users/nate/workspace/RMIServer/Interfaces.jar
-Djava.rmi.server.hostname=localhost
-Djava.security.policy=c:/Users/nate/workspace/RMIServer/src/server.policy
The compute engine seems to run just find and outputs the print statement in the code.
I then run the client with the defines:
-Djava.rmi.server.codebase=file:/c:/Users/nate/workspace/RMIClient/bin/
-Djava.security.policy=c:/Users/nate/workspace/RMIClient/src/client.policy
And I get the following error message:
RmiClientExample exception:
java.rmi.ServerException: RemoteException occurred in server thread; nested exception is:
java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is:
java.lang.ClassNotFoundException: client.GetAnswerTask
at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source)
at sun.rmi.transport.Transport$1.run(Unknown Source)
at sun.rmi.transport.Transport$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(Unknown Source)
at sun.rmi.transport.StreamRemoteCall.executeCall(Unknown Source)
at sun.rmi.server.UnicastRef.invoke(Unknown Source)
at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(Unknown Source)
at java.rmi.server.RemoteObjectInvocationHandler.invoke(Unknown Source)
at com.sun.proxy.$Proxy0.compute(Unknown Source)
at client.RmiClientExample.main(RmiClientExample.java:24)
Caused by: java.rmi.UnmarshalException: error unmarshalling arguments; nested exception is:
java.lang.ClassNotFoundException: client.GetAnswerTask
at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source)
at sun.rmi.transport.Transport$1.run(Unknown Source)
at sun.rmi.transport.Transport$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.lambda$run$0(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: client.GetAnswerTask
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.rmi.server.LoaderHandler$Loader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at sun.rmi.server.LoaderHandler.loadClassForName(Unknown Source)
at sun.rmi.server.LoaderHandler.loadClass(Unknown Source)
at sun.rmi.server.LoaderHandler.loadClass(Unknown Source)
at java.rmi.server.RMIClassLoader$2.loadClass(Unknown Source)
at java.rmi.server.RMIClassLoader.loadClass(Unknown Source)
at sun.rmi.server.MarshalInputStream.resolveClass(Unknown Source)
at java.io.ObjectInputStream.readNonProxyDesc(Unknown Source)
at java.io.ObjectInputStream.readClassDesc(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at sun.rmi.server.UnicastRef.unmarshalValue(Unknown Source)
at sun.rmi.server.UnicastServerRef.unmarshalParametersUnchecked(Unknown Source)
at sun.rmi.server.UnicastServerRef.unmarshalParameters(Unknown Source)
... 13 more
Any thoughts on what I might be doing wrong?

GetAnswerTask implements Serializable, so it will be serialized to the server when you call ComputeEngine_IF.compute(). So GetAnswerTask needs to be available at the server, on its classpath, and it isn't.

For those still struggling with oracle RMI tutorial, whose server doesn't download serializable class from given client's codebase (and stubbornly seeks class in its own codebase) - try to add
-Djava.rmi.server.useCodebaseOnly=false
to server's arguments

How to resolve exception in thread “main” javax.naming.NameNotFoundException: not bound?

I'm trying to create a jms publisher/subscriber chat application in eclipse.
import java.util.Properties;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageListener;
import javax.jms.TextMessage;
import javax.jms.Topic;
import javax.jms.TopicConnection;
import javax.jms.TopicConnectionFactory;
import javax.jms.TopicSession;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
public class TopicConsumer implements MessageListener {
public static void main(String[] args) throws JMSException, NamingException {
System.out.println(".....Entering JMS example TopicConsumer....");
Context context = TopicConsumer.getInitialContext();
TopicConnectionFactory topicConnectionFactory = (TopicConnectionFactory) context.lookup("ConnectionFactory");
Topic topic = (Topic) context.lookup("topic/zaneacademy_jms_tutorial_01");
TopicConnection topicConnection = topicConnectionFactory.createTopicConnection();
TopicSession topicSession = topicConnection.createTopicSession(false, TopicSession.AUTO_ACKNOWLEDGE);
topicSession.createSubscriber(topic).setMessageListener(new TopicConsumer());
topicConnection.start();
System.out.println("......Exiting JMS Example TopicConsumer.....");
}
public void onMessage(Message message) {
try {
System.out.println("Incoming Messages: " + ((TextMessage)message).getText());
} catch (JMSException e) {
e.printStackTrace();
}
}
public static Context getInitialContext() throws JMSException, NamingException {
Properties props = new Properties();
props.setProperty("java.naming.factory.initial", "org.jnp.interfaces.NamingContextFactory");
props.setProperty("java.naming.factory.url.pkgs", "org.jboss.naming");
props.setProperty("java.naming.provider.url", "localhost:1099");
Context context = new InitialContext(props);
return context;
}
}
trying to run the program I'm getting the following errors in console
.....Entering JMS example TopicConsumer....
Exception in thread "main" javax.naming.NameNotFoundException: zaneacademy_jms_tutorial_01 not bound
at org.jnp.server.NamingServer.getBinding(NamingServer.java:564)
at org.jnp.server.NamingServer.getBinding(NamingServer.java:572)
at org.jnp.server.NamingServer.getObject(NamingServer.java:578)
at org.jnp.server.NamingServer.lookup(NamingServer.java:317)
at org.jnp.server.NamingServer.lookup(NamingServer.java:291)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at sun.rmi.server.UnicastServerRef.dispatch(Unknown Source)
at sun.rmi.transport.Transport$1.run(Unknown Source)
at sun.rmi.transport.Transport$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(Unknown Source)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
at sun.rmi.transport.StreamRemoteCall.exceptionReceivedFromServer(Unknown Source)
at sun.rmi.transport.StreamRemoteCall.executeCall(Unknown Source)
at sun.rmi.server.UnicastRef.invoke(Unknown Source)
at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(Unknown Source)
at java.rmi.server.RemoteObjectInvocationHandler.invoke(Unknown Source)
at com.sun.proxy.$Proxy0.lookup(Unknown Source)
at org.jnp.interfaces.NamingContext.lookup(NamingContext.java:669)
at org.jnp.interfaces.NamingContext.lookup(NamingContext.java:629)
at javax.naming.InitialContext.lookup(Unknown Source)
at TopicConsumer.main(TopicConsumer.java:19)

As it says in the exception the zaneacademy_jms_tutorial_01 is not defined.
You need to configure it and assigne it to the topic/zaneacademy_jms_tutorial_01.
I would say, that the problem is your getInitialContext() which you configure mannaully, instead of returing the probably already configured context by new InitialContext();

Mongodb connection fails when selecting or inserting with java

I'm using mongo-java-driver-2.11.3.jar and also tried with mongo-2.10.1.jar both are giving the following error.The database is
connected but the collection insert and selection are not working.
import java.net.UnknownHostException;
import java.util.Set;
import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.MongoClient;
import com.mongodb.MongoException;
public class mongo_test {
public MongoClient mongo = null;
public DB mongodb = null;
private void mongo_startconnection() {
try {
mongo = new MongoClient("10.0.2.15", 27017);
mongodb = mongo.getDB("foobar");
System.out.println("Mongodb is connected");
BasicDBObject doc = new BasicDBObject();
DBCollection collection = mongodb.getCollection("url_ta");
Set<String> colls = mongodb.getCollectionNames();
for (String s : colls) {
System.out.println(s);
}
System.out.println("done");
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (MongoException e1) {
e1.printStackTrace();
}
}
public static void main(String args[]) {
mongo_test MT = new mongo_test();
MT.mongo_startconnection();
}
}
I'm getting this error:
Mongodb is connected
Nov 26, 2013 11:34:39 AM com.mongodb.DBTCPConnector initDirectConnection
WARNING: Exception executing isMaster command on /10.0.2.15:27017
java.net.SocketTimeoutException: connect timed out
at java.net.DualStackPlainSocketImpl.waitForConnect(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.SocksSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at com.mongodb.DBPort._open(DBPort.java:223)
at com.mongodb.DBPort.go(DBPort.java:125)
at com.mongodb.DBPort.go(DBPort.java:106)
at com.mongodb.DBPort.findOne(DBPort.java:162)
at com.mongodb.DBPort.runCommand(DBPort.java:170)
at com.mongodb.DBTCPConnector.initDirectConnection(DBTCPConnector.java:547)
at com.mongodb.DBTCPConnector.checkMaster(DBTCPConnector.java:526)
at com.mongodb.DBTCPConnector.innerCall(DBTCPConnector.java:236)
at com.mongodb.DBTCPConnector.call(DBTCPConnector.java:216)
at com.mongodb.DBApiLayer$MyCollection.__find(DBApiLayer.java:288)
at com.mongodb.DBApiLayer$MyCollection.__find(DBApiLayer.java:273)
at com.mongodb.DB.getCollectionNames(DB.java:400)
at mongo_test.mongo_startconnection(mongo_test.java:29)
at mongo_test.main(mongo_test.java:69)
com.mongodb.MongoException$Network: Read operation to server /10.0.2.15:27017 failed on database foobar at com.mongodb.DBTCPConnector.innerCall(DBTCPConnector.java:253)
at com.mongodb.DBTCPConnector.call(DBTCPConnector.java:216)
at com.mongodb.DBApiLayer$MyCollection.__find(DBApiLayer.java:288)
at com.mongodb.DBApiLayer$MyCollection.__find(DBApiLayer.java:273)
at com.mongodb.DB.getCollectionNames(DB.java:400)
at mongo_test.mongo_startconnection(mongo_test.java:29)
at mongo_test.main(mongo_test.java:69)
Caused by: java.net.SocketTimeoutException: connect timed out
at java.net.DualStackPlainSocketImpl.waitForConnect(Native Method)
at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
at java.net.PlainSocketImpl.connect(Unknown Source)
at java.net.SocksSocketImpl.connect(Unknown Source)
at java.net.Socket.connect(Unknown Source)
at com.mongodb.DBPort._open(DBPort.java:223)
at com.mongodb.DBPort.go(DBPort.java:125)
at com.mongodb.DBPort.call(DBPort.java:92)
at com.mongodb.DBTCPConnector.innerCall(DBTCPConnector.java:244)
... 6 more

1.Trying to find out whether your ip address and port number is reachable.
use command: telnet 10.0.2.15",27017 to check if such a port for this ip is open for connection.
2.If you have the authority to login the mongodb server ,just login and then:
If your mongodb is a cluster , Use commmand : ps -ef|grep mongos to check the mongodb server instance is up and the port is just
27017.
if your mongodb is just a single machine ,use ps -ef|grep mongod to make the same check.

package raamji.com.start;
//import com.mongodb.MongoClient;
import com.mongodb.Mongo;
import com.mongodb.MongoException;
import com.mongodb.WriteConcern;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.BasicDBObject;
import com.mongodb.DBObject;
import com.mongodb.DBCursor;
import com.mongodb.ServerAddress;
import java.net.UnknownHostException;
import java.util.Arrays;
public class Start {
public static void main(String[] args) throws UnknownHostException {
//crete Connection
Mongo mongoClient = new Mongo("ind-asingh", 27017);//or "localhost",27017
System.out.println("mongoClient :" + mongoClient);
DB db = mongoClient.getDB("DB Name");//e.g. MYDB
System.out.println("db :" + db);
//---------------------------Access your Collection-----------------------------
DBCollection collection = db.getCollection("message");
System.out.println("collection :" + collection);
System.out.println("Message Count: " + collection.getCount());
DBCursor cursor = collection.find();
try {
while (cursor.hasNext()) {
System.out.println(cursor.next());
}
} finally {
cursor.close();
}
}//end pf psvm
}//end of class