1. How will you retreive database warnings from a Connection object in JDBC?
//Retrieving warning from connection object
SQLWarning warning = conn.getWarnings();
//Retrieving next warning from warning object itself
SQLWarning nextWarning = warning.getNextWarning();
//Retrieving warning from statement object
stmt.getWarnings();
//Retrieving next warning from warning object itself
SQLWarning nextWarning = warning.getNextWarning();
//Retrieving warning from resultset object
rs.getWarnings();
//Retrieving next warning from warning object itself
SQLWarning nextWarning = warning.getNextWarning();
A
call to clearWarnings() method clears all warnings reported for this object. After a call to this method, the method getWarnings returns null until a new warning is reported for this object.
5. What happens when I try to call the getWarning() method on a connection/statement/resultset after it has been closed?
Trying to call the getWarning() method on either of these 3 objects
after they are closed will cause an SQLException to be thrown.
6. Let us say that I just closed my Statement object so, I cannot access the getWarning() on my statement. Can I still access the getWarning() on my ResultSet?
No. Closing a Statement automatically closes the ResultSet connected to
it. So, you will get the same SQLException if you try to do so.
7. What is DatabaseMetaData?
JDBC API has 2 Metadata interfaces DatabaseMetaData &
ResultSetMetaData. The DatabaseMetaData provides Comprehensive
information about the database as a whole. This interface is implemented
by driver vendors to let users know the capabilities of a Database
Management System (DBMS) in combination with the driver based on JDBC
technology ("JDBC driver") that is used with it. Use DatabaseMetaData to
find information about your database, such as its capabilities and
structure.
8. How will you use the DatabaseMetaData? Can you write a sample example code?
DatabaseMetaData md = conn.getMetaData();
System.out.println("Database Name: " + md.getDatabaseProductName());
System.out.println("Database Version: " + md.getDatabaseProductVersion());
System.out.println("Driver Name: " + md.getDriverName());
System.out.println("Driver Version: " + md.getDriverVersion());
9. What is ResultSetMetaData?
JDBC API has 2 Metadata interfaces DatabaseMetaData &
ResultSetMetaData. The ResultSetMetaData is an object that can be used
to get information about the types and properties of the columns in a
ResultSet object. Use ResultSetMetaData to find information about the
results of an
SQL query, such as size and types of columns.
10. How will you use the ResultSetMetaData? Can you write a sample example code?
ResultSet rs = stmt.executeQuery("SELECT * FROM TABLE_NAME");
ResultSetMetaData rsmd = rs.getMetaData();
int numberOfColumns = rsmd.getColumnCount();
boolean b = rsmd.isSearchable(1);
A RowSet is an object that encapsulates a set of rows from either Java Database Connectivity (JDBC) result sets or tabular
data sources like a file or spreadsheet.
12. Why do we need a RowSet?
RowSet is a interface that adds support to the JDBC API for the
JavaBeans component model. A rowset, which can be used as a JavaBeans
component in a visual Bean development environment, can be created and
configured
at design time and
executed at run time. The RowSet interface provides a set of JavaBeans
properties that allow a RowSet instance to be configured to connect to a
JDBC
data source and read some data from the data source.
A group of setter methods (setInt, setBytes, setString, and so on)
provide a way to pass input parameters to a rowset's command property.
This command is the SQL query the rowset uses when it gets its data from
a relational database, which is generally the case. Rowsets are easy to
use since the RowSet interface extends the standard java.sql.ResultSet
interface so it has all the methods of ResultSet
13. What are the advantages of using RowSet over ResultSet?
There are two clear advantages of using RowSet over ResultSet:
* RowSet makes it possible to use the ResultSet object as a JavaBeans component.
* RowSet be used to make a ResultSet object scrollable and updatable.
All RowSet objects are by default scrollable and updatable. If the
driver and database being used do not support scrolling and/or updating
of result sets, an application can populate a RowSet object
implementation (e.g. JdbcRowSet) with the data of a ResultSet object and
then operate on the RowSet object as if it were the ResultSet object.
14. What are the different types of RowSet ?
There are two types of RowSet are there. They are:
* Connected - A connected RowSet object connects to the database once and remains connected until the application terminates.
* Disconnected - A disconnected RowSet object connects to the database,
executes a query to retrieve the data from the database and then closes
the
connection. A program may
change the data in a disconnected RowSet while it is disconnected.
Modified data can be updated in the database after a disconnected RowSet
reestablishes the connection with the database.
15. Can you give an example of Connected RowSet?
A JdbcRowSet object is a example of connected RowSet, which means it continually maintains its connection to a database using a JDBC technology-enabled driver.
16. Can you give an example of Disconnected RowSet?
A CachedRowSet object is a example of disconnected rowset, which means that it makes use of a connection to its data source only briefly. It connects to its data source while it is reading data to populate itself with rows and again while it is propagating changes back to its underlying data source.
The rest of the time, a CachedRowSet object is disconnected, including
while its data is being modified. Being disconnected makes a RowSet
object much leaner and therefore much easier to pass to another
component. For example, a disconnected RowSet object can be serialized
and passed over the wire to a thin client such as a
personal digital assistant (PDA).
17. What are the benefits of having JdbcRowSet implementation?
The JdbcRowSet implementation is a wrapper around a ResultSet object that has following advantages over ResultSet
* This implementation makes it possible to use the ResultSet object as a
JavaBeans component. A JdbcRowSet can be used as a JavaBeans component
in a visual Bean development environment, can be created and configured at design time and executed at run time.
* It can be used to make a ResultSet object scrollable and updatable.
All RowSet objects are by default scrollable and updatable. If the
driver and database being used do not support scrolling and/or updating
of result sets, an application can populate a JdbcRowSet object with the
data of a ResultSet object and then operate on the JdbcRowSet object as
if it were the ResultSet object.
18. What is the need of BatchUpdates feature in JDBC?
The BatchUpdates feature allows us to group SQL statements together and
send to database server in one single shot instead of multiple calls.
19. What is a DataSource?
A DataSource object is the representation of a source of data in the Java programming language.
In basic terms:
* A DataSource is a facility for storing data.
* DataSource can be referenced by JNDI.
* Data Source may point to RDBMS, file System , any DBMS etc..
Typically in enterprise application perspective, the term DataSource can
be used interchangeably with a RDBMS database because in almost all
cases, our DataSource will be pointing to an RDBMS database.
20. What are the advantages of DataSource?
The few advantages of using data source are :
* An application does not need to hardcode driver information, as it does with the DriverManager.
* The DataSource implementations can easily change the properties of
data sources. For example: There is no need to modify the application
code when making changes to the database details.
* The DataSource facility allows developers to implement a DataSource
class to take advantage of features like connection pooling and
distributed transactions.
21. What is the difference between a Statement and a PreparedStatement?
Some of the main differences between a statement & PreparedStatement are:
| Statement | PreparedStatment |
| A standard Statement is used to create a Java representation of a literal SQL statement and execute it on the database. |
A PreparedStatement is a precompiled statement. This means that when
the PreparedStatement is executed, the RDBMS can just run the
PreparedStatement SQL statement without having to compile it first. |
| Statement has to verify its metadata against the database every time. | A prepared statement has to verify its metadata against the database only once. |
| If you want to execute the SQL statement once go for STATEMENT |
If you want to execute a single SQL statement multiple number of times,
then go for PREPAREDSTATEMENT. PreparedStatement objects can be reused
with passing different values to the queries. |
22. What’s the difference between TYPE_SCROLL_INSENSITIVE and TYPE_SCROLL_SENSITIVE in ResultSets?
Some of the main differences between a TYPE_SCROLL_INSENSITIVE & TYPE_SCROLL_SENSITIVE are:
| TYPE_SCROLL_INSENSITIVE | TYPE_SCROLL_SENSITIVE |
| An insensitive resultset is like the snapshot of the data in the database when query was executed. |
A sensitive resultset does NOT represent a snapshot of data, rather it
contains points to those rows which satisfy the query condition. |
| After we get the resultset the changes made to data are not
visible through the resultset, and hence they are known as insensitive. | After we obtain the resultset if the data is modified then such modifications are visible through resultset. |
| Performance not effected with insensitive. | Since a trip is made for every ‘get’ operation, the performance drastically get affected. |
