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Java Articles
Page 420 of 450
What is ResultSetMetaData in JDBC? What is its significance?
The ResultSetMetaData provides information about the obtained ResultSet object like, the number of columns, names of the columns, datatypes of the columns, name of the table etc…Following are some methods of ResultSetMetaData class.MethodDescriptiongetColumnCount()Retrieves the number of columns in the current ResultSet object.getColumnLabel()Retrieves the suggested name of the column for use.getColumnName()Retrieves the name of the column.getTableName()Retrieves the name of the table.Exampleimport java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.ResultSetMetaData; import java.sql.Statement; public class ResultSetMetadataExample { public static void main(String args[]) throws Exception { //Registering the Driver DriverManager.registerDriver(new com.mysql.jdbc.Driver()); //Getting the connection ...
Read MoreWhat is DatabaseMetaData in JDBC? What is its significance?
Generally, Data about data is known as metadata. The DatabaseMetaData interface provides methods to get information about the database you have connected with like, database name, database driver version, maximum column length etc...Following are some methods of DatabaseMetaData class.MethodDescriptiongetDriverName()Retrieves the name of the current JDBC drivergetDriverVersion()Retrieves the version of the current JDBC drivergetUserName()Retrieves the user name.getDatabaseProductName()Retrieves the name of the current database.getDatabaseProductVersion()Retrieves the version of the current database.getNumericFunctions()Retrieves the list of the numeric functions available with this database.getStringFunctions()Retrieves the list of the numeric functions available with this database.getSystemFunctions()Retrieves the list of the system functions available with this database.getTimeDateFunctions()Retrieves the list ...
Read MoreHow many locking systems are there in JDBC?
You can lock a record, set of records, database table, table-space etc. and when we do we cannot change the locked values. Following are the types of locking in JDBC:Row and Key Locks: These are used to lock a particular row. Using these locks, you can achieve concurrency.Page Locks: These are used to lock a page. If you apply this, whenever the contents of a row changes, the database locks the entire page which holds the row. If you need to update/change large number of rows at once you can use this lock.Table Locks: You can lock a table using ...
Read MoreWhat is the use of the method setAutoCommit() in JDBC?
If you commit a database, it saves all the changes that have been done till that particular point.You can commit a database using the commit() method. Whenever any issue occurs you can revert the database to this point using the rollback() method. By default, some databases commit the databases automatically. But, while managing transactions you need to commit the database manually.In this scenario you can use the setAutoCommit() method. This method belongs to the Connection interface and, it accepts a boolean value.If you pass true to this method it turns on the auto-commit feature of the database and, if you ...
Read MoreHow many types of Result Sets are there in JDBC What are they?
There are two types of result sets namely, forward only and, bidirectional.Forward only ResultSet: The ResultSet object whose cursor moves only in one direction is known as forward only ResultSet. By default, JDBC result sets are forward-only result sets.You can move the cursor of the forward only ResultSets using the next() method of the ResultSet interface. It moves the pointer to the next row from the current position. This method returns a boolean value. If there are no rows next to its current position it returns false, else it returns true.Therefore, using this method in the while loop you can ...
Read MoreWhat are the important methods of the SQLException class?
An SQLException can occur both in the driver and the database. When such an exception occurs, an object of type SQLException will be passed to the catch clause.The passed SQLException object has the following methods available for retrieving additional information about the exception:MethodDescriptiongetErrorCode( )Gets the error number associated with the exception.getMessage( )Gets the JDBC driver's error message for an error, handled by the driver or gets the Oracle error number and message for a database error.getSQLState( )Gets the XOPEN SQLstate string. For a JDBC driver error, no useful information is returned from this method. For a database error, the five-digit ...
Read MoreWhat is JDBC SQL Escape Syntax Explain?
The escape syntax gives you the flexibility to use database specific features unavailable to you by using standard JDBC methods and properties.The general SQL escape syntax format is as follow:{keyword 'parameters'}Following are various escape syntaxes in JDBC:d, t, ts Keywords: They help identify date, time, and timestamp literals. As you know, no two DBMSs represent time and date the same way. This escape syntax tells the driver to render the date or time in the target database's format{d 'yyyy-mm-dd'}Where yyyy = year, mm = month; dd = date. Using this syntax {d '2009-09-03'} is March 9, 2009.Example//Create a Statement object ...
Read MoreAs HTTP is a stateless then how to maintain the session between web browser and web server?
HTTP is a "stateless" protocol which means each time a client retrieves a Webpage, the client opens a separate connection to the Web server and the server automatically does not keep any record of previous client request.Maintaining Session Between Web Client And ServerLet us now discuss a few options to maintain the session between the Web Client and the Web Server −CookiesA webserver can assign a unique session ID as a cookie to each web client and for subsequent requests from the client they can be recognized using the received cookie.This may not be an effective way as the browser ...
Read MoreWhat is a hit count for a Webpage?
A hit counter tells you about the number of visits on a particular page of your web site. Usually, you attach a hit counter with your index.jsp page assuming people first land on your home page.To implement a hit counter you can make use of the Application Implicit object and associated methods getAttribute() and setAttribute().This object is a representation of the JSP page through its entire lifecycle. This object is created when the JSP page is initialized and will be removed when the JSP page is removed by the jspDestroy() method.Following is the syntax to set a variable at the ...
Read MoreHow can you implement hit counter to avoid loss of count data with each restart of the application in JSP?
When you restart your application, i.e., web server, this will reset your application variable and your hit counter will reset to zero. To avoid this loss, consider the following points −Define a database table with a single count, let us say hitcount. Assign a zero value to it.With every hit, read the table to get the value of hitcount.Increase the value of hitcount by one and update the table with the new value.Display the new value of hitcount as a total page hit counts.If you want to count hits for all the pages, implement above logic for all the pages.
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