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how can i handle multiple server MongoDB

Hi all i am new to spring maven project, and i am using MongoDB. I want to use two tomcats/ MongoDB both of theri IP address are different. when first DB is down i need to connect with second one how it is possible
I am using following code
public boolean mongoRunningAt(String uri) {
try {
Mongo mongo = new Mongo(new MongoURI(uri));
try {
Socket socket = mongo.getMongoOptions().socketFactory.createSocket();
socket.connect(mongo.getAddress().getSocketAddress());
socket.close();
} catch (IOException ex) {
mongo = new Mongo(new MongoURI(uri_second));
Socket socket = mongo.getMongoOptions().socketFactory.createSocket();
socket.connect(mongo.getAddress().getSocketAddress());
socket.close();
//return false;
}
mongo.close();
return true;
} catch (UnknownHostException e) {
return false;
}
}
Using this code i tried with first one successfully connected, now stoped first DB now restarted server it is connected with second db.
But if i didn't restart server it is always pointing to First only... how should i work on this
Thanks in advance

You deployed 2 servers, are they in a replica set. If not you can follow the link.
When they are already in a replica set you can use a connectionstring containing the 2 servers.
Like this:
mongodb://db1.example.net,db2.example.net:2500/?replicaSet=test

try-catch-finally block in java

As per my understanding, I want to follow the best practice for releasing the resources at the end to prevent any connection leaks. Here is my code in HelperClass.
public static DynamoDB getDynamoDBConnection()
{
try
{
dynamoDB = new DynamoDB(new AmazonDynamoDBClient(new ProfileCredentialsProvider()));
}
catch(AmazonServiceException ase)
{
//ase.printStackTrace();
slf4jLogger.error(ase.getMessage());
slf4jLogger.error(ase.getStackTrace());
slf4jLogger.error(ase);
}
catch (Exception e)
{
slf4jLogger.error(e);
slf4jLogger.error(e.getStackTrace());
slf4jLogger.error(e.getMessage());
}
finally
{
dynamoDB.shutdown();
}
return dynamoDB;
}
My doubt is, since the finally block will be executed no matter what, will the dynamoDB returns empty connection because it will be closed in finally block and then execute the return statement? TIA.

Your understanding is correct. dynamoBD.shutdown() will always execute before return dynamoDB.
I'm not familiar with the framework you're working with, but I would probably organize the code as follows:
public static DynamoDB getDynamoDBConnection()
throws ApplicationSpecificException {
try {
return new DynamoDB(new AmazonDynamoDBClient(
new ProfileCredentialsProvider()));
} catch(AmazonServiceException ase) {
slf4jLogger.error(ase.getMessage());
slf4jLogger.error(ase.getStackTrace());
slf4jLogger.error(ase);
throw new ApplicationSpecificException("some good message", ase);
}
}
and use it as
DynamoDB con = null;
try {
con = getDynamoDBConnection();
// Do whatever you need to do with con
} catch (ApplicationSpecificException e) {
// deal with it gracefully
} finally {
if (con != null)
con.shutdown();
}
You could also create an AutoCloseable wrapper for your dynamoDB connection (that calls shutdown inside close) and do
try (DynamoDB con = getDynamoDBConnection()) {
// Do whatever you need to do with con
} catch (ApplicationSpecificException e) {
// deal with it gracefully
}

Yes,dynamoDB will return an empty connection as dynamoBD.shutdow() will be executed before return statement, Always.

Although I am not answering your question about the finally block being executed always (there are several answers to that question already), I would like to share some information about how DynamoDB clients are expected to be used.
The DynamoDB client is a thread-safe object and is intended to be shared between multiple threads - you can create a global one for your application and re-use the object where ever you need it. Generally, the client creation is managed by some sort of IoC container (Spring IoC container for example) and then provided by the container to whatever code needs it through dependency injection.
Underneath the hood, the DynamoDB client maintains a pool of HTTP connections for communicating the DynamoDB endpoint and uses connections from within this pool. The various parameters of the pool can be configured by passing an instance of the ClientConfiguration object when constructing the client. For example, one of the parameters is the maximum number of open HTTP connections allowed.
With the above understanding, I would say that since the DynamoDB client manages the lifecycle of HTTP connections, resource leaks shouldn't really be concern of code that uses the DynamoDB client.

How about we "imitate" the error and see what happens ? This is what I mean:
___Case 1___
try{
// dynamoDB = new DynamoDB(new AmazonDynamoDBClient(new ProfileCredentialsProvider()));
throw new AmazonServiceException("Whatever parameters required to instantiate this exception");
} catch(AmazonServiceException ase)
{
//ase.printStackTrace();
slf4jLogger.error(ase.getMessage());
slf4jLogger.error(ase.getStackTrace());
slf4jLogger.error(ase);
}
catch (Exception e)
{
slf4jLogger.error(e);
slf4jLogger.error(e.getStackTrace());
slf4jLogger.error(e.getMessage());
}
finally
{
//dynamoDB.shutdown();
slf4jLogger.info("Database gracefully shutdowned");
}
___Case 2___
try{
// dynamoDB = new DynamoDB(new AmazonDynamoDBClient(new ProfileCredentialsProvider()));
throw new Exception("Whatever parameters required to instantiate this exception");
} catch(AmazonServiceException ase)
{
//ase.printStackTrace();
slf4jLogger.error(ase.getMessage());
slf4jLogger.error(ase.getStackTrace());
slf4jLogger.error(ase);
}
catch (Exception e)
{
slf4jLogger.error(e);
slf4jLogger.error(e.getStackTrace());
slf4jLogger.error(e.getMessage());
}
finally
{
//dynamoDB.shutdown();
slf4jLogger.info("Database gracefully shutdowned");
}
These exercise could be a perfect place to use unit tests and more specifically mock tests. I suggest you to take a close look at JMockit, which will help you write such tests much more easily.

How to implement shutdown hook handler in google appengine

How to implement shutdown hook handler in google appengine . Im not understanding their doc here https://developers.google.com/appengine/docs/java/backends/overview#Shutdown. what i need is, i need to be notified in the code when backend is stopped due to any to reason.
this is my code
try{
while (haveMoreWork() &&
!LifecycleManager.getInstance().isShuttingDown()) {
process(); // this is my function to read all the data.if it fails because of termination.i need to be notified.
}catch(Exception e){
log.log(Level.SEVERE, e.getMessage(), e);
log.severe("error occured"+e);
log.info("failed ");
}

You need to use the hook instead of the status report:
LifecycleManager.getInstance().setShutdownHook(new ShutdownHook() {
public void shutdown() {
// code
}
});

How to create a "FTPS" Mock Server to unit test File Transfer in Java

I have a CreateFTPConnection class which create a FTPS connection. Using this connection, files are transferred. Here is the code of TransferFile class
public class TransferFile
{
private CreateFTPConnection ftpConnection;
private FTPSClient client;
public TransferFile(CreateFTPConnection ftpConnection) {
this.ftpConnection = ftpConnection;
this.client = ftpConnection.getClient();
}
public void transfer(Message<?> msg)
{
InputStream inputStream = null;
try
{
if(!client.isConnected()){
ftpConnection.init();
client = ftpConnection.getClient();
}
File file = (File) msg.getPayload();
inputStream = new FileInputStream(file);
client.storeFile(file.getName(), inputStream);
client.sendNoOp();
} catch (Exception e) {
try
{
client.disconnect();
}
catch (IOException e1) {
e1.printStackTrace();
}
}
finally
{
try {
inputStream.close();
}
catch (IOException e) {
e.printStackTrace();
}
}
}
}
I have to write jUnit Testcase for this class. For this, I have to create a FTPS Mock Server connection and have to use that connection to test the File Transfer. So can anyone plz give me any idea of how to make FTPS Mock Server and do the test case. I googled on this, but what I get is on FTP or SFTP, not FTPS. Please help me.

You might find this useful MockFTPServer
The issue is that these mock servers don't implement the TLS portion from what I can see. You may need to do a little work to allow connections via TLS.
You should be able to search around and find some articles here on SO about dealing with certificates, (or in some cases, bypassing them) for the sake of your testing.
Here's another Article that goes through the steps of creating a basic FTP server Test.
Short of a full blown FTP server (Apache http w/ mod_ftp add on), there doesn't seem to be anything useful to do this.

ActiveMQ register listener to StompConnection

I'm using a variation of the example at http://svn.apache.org/repos/asf/activemq/trunk/assembly/src/release/example/src/StompExample.java to receive message from a queue. What I'm trying to do is to keep listening to a queue and perform some action upon reception of a new message. The problem is that I couldn't find a way to register a listener to any of the related objects. I've tried something like:
public static void main(String args[]) throws Exception {
StompConnection connection = null;
try {
connection = new StompConnection();
connection.open("localhost", 61613);
connection.connect("admin", "activemq");
connection.subscribe("/queue/worker", Subscribe.AckModeValues.AUTO);
while (true) {
StompFrame message = connection.receive();
System.out.println(message.getBody());
}
} catch (UnknownHostException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
} finally {
if (connection != null) {
connection.disconnect();
}
}
}
but this doesn't work as a time out occurs after a few seconds (java.net.SocketTimeoutException: Read timed out). Is there anything I can do to indefinitely listen to this queue?

ActiveMQ's StompConnection class is a relatively primitive STOMP client. Its not capable of async callbacks on Message or for indefinite waits. You can pass a timeout to receive but depending on whether you are using STOMP v1.1 it could still timeout early if a heart-beat isn't received in time. You can of course always catch the timeout exception and try again.
For STOMP via Java you're better off using StompJMS or the like which behaves like a real JMS client and allows for async Message receipt.

#Tim Bish: I tried StompJMS, but couldn't find any example that I could use (maybe you can provide a link). I 'fixed' the problem by setting the timeout to 0 which seems to be blocking.

even i was facing the same issue.. you can fix this by adding time out to your receive() method.
Declare a long type variable.
long waitTimeOut = 5000; //this is 5 seconds
now modify your receive function like below.
StompFrame message = connection.receive(waitTimeOut);
This will definitely work.