WIPRO Core Java Campus Interview Question Answer

What is 2 phase commit?

A 2-phase commit is an algorithm used to ensure the integrity of a committing transaction. In Phase 1, the transaction coordinator contacts potential participants in the transaction. The participants all agree to make the results of the transaction permanent but do not do so immediately. The participants log information to disk to ensure they can complete In phase 2 f all the participants agree to commit, the coordinator logs that agreement and the outcome is decided. The recording of this agreement in the log ends in Phase 2, the coordinator informs each participant of the decision, and they permanently update their resources.

How do you handle your own transaction ?

Connection Object has a method called setAutocommit(Boolean istrue)
- Default is true. Set the Parameter to false , and begin your transaction

What is the normal procedure followed by a java client to access the db.?

connection is created in 3 steps:
A. Find a proper database URL
B. Load the database driver
C. Ask the Java DriverManager class to open a connection to your database
In java code, the steps are realized in code as follows:
D. Create a properly formatted JDBR URL for your database. (See FAQ on JDBC URL for more information). A JDBC URL has the form jdbc:someSubProtocol://myDatabaseServer/theDatabaseName
E. Class.forName(”my.database.driver”);
F. Connection conn = DriverManager.getConnection(”a.JDBC.URL”, “databaseLogin”,”databasePassword”);

What is a data source?

A DataSource class brings another level of abstraction than directly using a connection object. Data source can be referenced by JNDI. Data Source may point to RDBMS, file System , any DBMS etc.

What are collection pools? What are the advantages?

- A connection pool is a cache of database connections that is maintained in memory, so that the connections may be reused 18. How do you get Column names only for a table (SQL Server)? Write the Query. -

19. select name from syscolumns

20. where id=(select id from sysobjects where name='user_hdr')

21. order by colid --user_hdr is the table name

What are the types of messaging?

There are two kinds of Messaging. Synchronous messaging involves a client that waits for the server to respond to a message. Asynchronous messaging involves a client that does not wait for a message from the server. An event is used to trigger a message from a server.

What is publish/subscribe messaging?

With publish/subscribe message passing the sending application/client establishes a named topic in the JMS broker/server and publishes messages to this queue. The receiving clients register (specifically, subscribe) via the broker to messages by topic; every subscriber to a topic receives each message published to that topic. There is a one-to-many relationship between the publishing client and the subscribing clients.

Why doesn’t the JMS API provide end-to-end synchronous message delivery and notification of delivery?

Some messaging systems provide synchronous delivery to destinations as a mechanism for implementing reliable applications. Some systems provide clients with various forms of delivery notification so that the clients can detect dropped or ignored messages. This is not the model defined by the JMS API. JMS API messaging provides guaranteed delivery via the once-and-only-once delivery semantics of PERSISTENT messages. In addition, message consumers can insure reliable processing of messages by using either CLIENT_ACKNOWLEDGE mode or transacted sessions. This achieves reliable delivery with minimum synchronization and is the enterprise messaging model most vendors and developers prefer. The JMS API does not define a schema of systems messages (such as delivery notifications). If an application requires acknowledgment of message receipt, it can define an application-level acknowledgment message.

What are the core JMS-related objects required for each JMS-enabled application?

Each JMS-enabled client must establish the following: A connection object provided by the JMS server (the message broker)

Within a connection, one or more sessions, which provide a context for message sending and receiving

Within a session, either a queue or topic object representing the destination (the message staging area) within the message broker

Within a session, the appropriate sender or publisher or receiver or subscriber object (depending on whether the client is a message producer or consumer and uses a point-to-point or publish/subscribe strategy, respectively). Within a session, a message object (to send or to receive)

What is the Role of the JMS Provider?

The JMS provider handles security of the messages, data conversion and the client triggering. The JMS provider specifies the level of encryption and the security level of the message, the best data type for the non-JMS client.

How does a typical client perform the communication?

A. Use JNDI to locate administrative objects.
B. Locate a single ConnectionFactory object.

C. Locate one or more Destination objects.

D. Use the ConnectionFactory to create a JMS Connection.

E. Use the Connection to create one or more Session(s).

F. Use a Session and the Destinations to create the MessageProducers and MessageConsumers needed.

G. Perform your communication.

Give an example of using the point-to-point model?

The point-to-point model is used when the information is specific to a single client. For example, a client can send a message for a print out, and the server can send information back to this client after completion of the print job.

How does the Application server handle the JMS Connection?

App server creates the server session and stores them in a pool. A. Connection consumer uses the server session to put messages in the session of the JMS.

B. Server session is the one that spawns the JMS session.

C. Applications written by Application programmers creates the message listener.

What are the implicit objects?

Implicit objects are objects that are created by the web container and contain information related to a particular request, page, or application. They are: request, response, pageContext, session, application, out, config, page, exception.