What is JDBC?
J
• JDBC is: Java Database Connectivity
– is
i a Java
J
API for
f connecting
ti programs written
itt in
i Java
J
to
t
the data in relational databases.
– consists of a set of classes and interfaces written in the
Java programming language.
– is used for accessing databases from Java applications.
• JDBC:
–
–
–
–
establishes a connection with a database
sends SQL statements
processes the results
sends back the results.
JDBC Architecture
Application
•
•
•
•
JDBC
Driver
Java code calls JDBC library
JDBC loads a driver
Driver talks to a particular database
Can have more than one driver -> more than one
database
• Ideal: can change database engines without changing
any application code
• JDBC is used by Java programmers to connect
to databases
• With a small "bridge" program, you can use the
JDBC iinterface
f to access ODBC
ODBC--accessible
ibl
databases.
• Open Database Connectivity (ODBC
ODBC))
provides a standard software API method for
using database management systems (DBMS).
(DBMS)
The designers of ODBC aimed to make it
independent of programming languages
languages,
database systems, and operating systems.
JDBC API
• The JDBC API supports both twotwo-tier and
three--tier models for database access.
three
• Two
Two--tier model -- a Java applet or application
interacts directly with the database.
• Three
Three--tier model -- introduces a middle
middle--level
server for execution of business logic:
– the middle tier to maintain control over data
access.
JDBC Drivers
•
•
•
•
Type I: “JDBC“JDBC
JDBC-ODBC bridge driver
driver”
Type II: “Native“Native-API partly Java driver”
T
Type
III:
III “JDBC“JDBC-Net
N pure JJava ddriver”
i ”
Type IV: “Native protocol pure Java driver”
JDBC Architectures
Java Application
JDBC driver manager
g
JDBC/ODBC
bridge
JDBC/native
bridge
ODBC Driver
Native driver
(DBMS specific)
JDBC middleware JDBC Driver
(various DBMS) (DBMS Specific)
DBMS
JDBC Class Usage
DriverManager
Driver
Connection
Statement
ResultSet
The JDBC Steps
1. Importing Packages
2. Registering the JDBC Drivers
3 Opening a Connection to a Database
3.
4. Creating a Statement Object
5 Executing
5.
E
i a Query
Q
andd Returning
R
i aR
Result
l Set
S
Object
6 Processing
6.
P
i the
h Result
R l Set
S
7. Closing the Statement Object
8. Closing the Connection
1) Importing Packages
import java.sql.*;
2) Registering the driver
Class.forName
("sun.jdbc.odbc.JdbcOdbcDriver");
OR
Driver d=new
sun.jdbc.odbc.JdbcOdbcDriver();
jdb db db Odb D i ()
g
g
( );
DriverManager.registerDriver(d);
3)) Connecting
g to DataBase
Connection con =
DriverManager.getConnection
DriverManager getConnection
(jdbc:odbc:datasourcename,
”username”, ”password”);
4) Create a statement object
Statement stmt=con.createStatement();
5) Executing a Query and returning a
ResultSet object
ResultSet rs
rs= stmt.executeQuery
( “SELECT * from authors”);
6) Close the statement and the
connection
stmt.close();
con close();
con.close();
Statement Methods
ResultSet executeQuery(String)
– Execute a SQL statement that returns a
single ResultSet.
i t executeUpdate(String)
int
t U d t (St i )
– Execute a SQL INSERT, UPDATE or
DELETE statement. Returns the number
of rows changed.
boolean execute(String)
– Execute a SQL
Q statement and returns a
boolean value.
ResultSet
• A ResultSet provides access to a table of data
generated
db
by executing
i aS
Statement.
• Only one ResultSet per Statement can be open
at once.
• The table rows are retrieved in sequence.
q
• A ResultSet maintains a cursor pointing to its
current row of data.
• The 'next' method moves the cursor to the next
row.
row
– you can’t rewind
while(rs.next())
{
System.out.println(rs.getString(1) + " " +
rs.getString(2) + " " +
rs.getString(3));
g
g( ));
}
First column has index 11, not 0
– The ResultSet provides getXxx methods that
take a column index or column name and
returns the data
– Can also access result meta data (column
names, etc.)
ResultSet Methods
• Type getType(int columnIndex)
– returns
t
the
th given
i
field
fi ld as th
the given
i
type
• Type getType(String columnName)
– same,
same but uses name of field
– less efficient
A Simple JDBC application
loadDriver
getConnection
createStatement
execute(SQL)
Result handling
yes
More
M
results
no
closeStatment
closeConnection
import java.sql.*;
public
bli class
l
jdb
jdbctest
t t{
public static void main(String args[]){
try{
Class.forName(“sun.jdbc.odbc.JdbcOdbcDriver");
Connection con = DriverManager.getConnection
((“jdbc:odbc:mydatasource",
jdbc:odbc:mydatasource , "user",
user , "passwd");
passwd );
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery
(" l t name, number
("select
b ffrom pcmtable
t bl where
h
number
b
< 2");
while(rs.next())
System.out.println(rs.getString(1) + " (" +
rs.getInt(2) + ")");
stmt.close()
con.close();
} catch(Exception e){ }}}
Scrollable ResultSet
St t
Statement
t createStatement(
t St t
t( resultSetType,
ltS tT
resultSetConcurrency)
ltS tC
)
• resultSetType
resultSetType::
• ResultSet.TYPE_FORWARD_ONLY
R l S TYPE FORWARD ONLY
-allows only forward movement of the cursor
• ResultSet.TYPE_SCROLL_INSENSITIVE
R l S TYPE SCROLL INSENSITIVE
-backwards, forwards, random cursor movement.
-does
d
nott reflect
r fl t the
th changes
h
in
i the
th data.
d t
• ResultSetTYPE_SCROLL_SENSITIVE
-backwards,
backwards forwards
forwards, random cursor movement
movement.
- reflect the changes in the data.
Scrollable ResultSet (cont’d)
• resultSetConcurrency:
• ResultSet.CONCUR_READ_ONLY
ResultSet.CONCUR READ ONLY
This is the default and allows only data to be read from the database.
• ResultSet.CONCUR_UPDATABLE
This option allows to make changes to the database based on new
methods and positioning ability of the cursor.
• Example:
Statement stmt = con.createStatement(
ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
R
ResultSet
ltS t rs= stmt.executeQuery(str);
t t
t Q
( t )
public boolean absolute(int row) throws
SQLException
• -If the given row number is positive, this method moves the cursor
to the given row number (with the first row numbered 1).
• -If the row number is negative, the cursor moves to a relative
position from the last row.
• -If the row number
b is 0, an SQLException will b
be raised.
d
public
bli b
boolean
l
relative(int
l ti (i t row)
) th
throws
SQLException
• Shifts the control of a result set cursor,
cursor forward or backward,
backward
relative to the row number that you specify as a parameter. This
method accepts either a positive or negative value as a parameter.
Scrollable ResultSet (cont’d)
public boolean first()
public boolean last()
public boolean previous()
public boolean next()
p
()
public void beforeFirst()
public
p
void afterLast()
()
public boolean isFirst()
public boolean isLast()
p
public boolean isAfterLast()
public boolean isBeforeFirst()
public int getRow()
Updatable ResultSet
•
•
•
•
•
void updateRow()
void insertRow()
void
id ddeleteRow()
l R ()
void updateString()
void updateInt()
About Prepared Statements
• Allows you to pass runtime parameters to
the SQL statements to query and modify the
data in a table
table.
• Also used for queries that are executed many
times.
p
and p
prepared
p
onlyy once byy JJDBC.
• Complied
• Helps in reducing the load on the database
server and thus improving the performance
of the application
application.
• Instead of values, use ‘?
‘?’.
• Hence, Prepared Statements can be thought
of as statements that contain placeholders to
be substituted later with actual values.
Querying with
PreparedStatement
P
dSt t
t
String str =
"SELECT * FROM employee " +
"WHERE emp_id= ? and salary > ?";
PreparedStatement ps =
con.prepareStatement(str);
p p
( );
ps.setString(1, "34562");
ps.setInt(2, 26000);
R
ResultSet
ltS t rs = ps.executeQuery();
t Q
()
Updating with
PreparedStatement
String str =
“DELETE FROM employee
l
"+
"WHERE emp_id = ? and salary > ?";
PreparedStatement ps = con.prepareStatement(str);
ps.setString(1, "34562");
ps.setDouble(2, 26000);
int count = ps.executeUpdate();
Statements vs.
P
PreparedStatements
dS
• Are these the same? What do they do?
String val = "abc";
PreparedStatement ps =
con.prepareStatement("select * from R where A=?");
ps.setString(1,
p
g( val);
)
ResultSet rs = pstmt.executeQuery();
String val = "abc";
abc ;
Statement stmt = con.createStatement( );
ResultSet rs =
stmt.executeQuery("select * from R where A=" + val);
Statements vs.
P
PreparedStatements
dS
• Will this work?
PreparedStatement ps =
con prepareStatement("select
con.prepareStatement(
select * from ?");
? );
ps.setString(1, myFavoriteTableString);
• No!!! A ‘?’ can onlyy be used to represent
p
a
column value
Transactions and JDBC
• Transaction: more than one statement that must
all succeed (or all fail) together
– e.g., updating several tables due to customer purchase
• If one fails, the system must reverse all previous
actions
• Also can’t leave DB in inconsistent state halfway
through a transaction
• COMMIT = complete transaction
• ROLLBACK = cancel all actions
Example
• Suppose we want to transfer money from bank account 13
to account 72:
PreparedStatement ps =
con.prepareStatement("update BankAccount
sett amountt = amountt + ?
where accountId = ?");
ps setInt(1 -100);
ps.setInt(1,-100);
ps.setInt(2, 13);
p
ps.executeUpdate();
p
();
What happens if this
ps.setInt(1, 100);
update fails?
ps.setInt(2, 72);
ps.executeUpdate();
Transaction Management
• Transactions are not explicitly opened and closed
• The connection has a state called AutoCommit
mode
d
• if AutoCommit is true
true,, then every statement is
automatically committed
• if AutoCommit is false
false,, then everyy statement is
added to an ongoing transaction
• Default: true
AutoCommit
setAutoCommit(boolean
(
val))
• If you set AutoCommit to false, you must explicitly
commit or rollback the transaction using
con.commit() and con.rollback()
• Note: DDL statements (e.g., creating/deleting
tables) in a transaction may be ignored or may cause
a commit to occur
Save Points
Statement st
st=con
con.createStatement(
createStatement( );
st.executeUpdate(str1);
S
Savepoint
i svpt=con.setSavepoint(
S
i ( ));
st.executeUpdate(str2);
if(…) conn.rollback(svpt);
….
con.commit( );
Batch Updates
• A batch is a group of update statements that are
sent to a database to be executed as a single unit.
• You can send the batch to a database in a single
g
request using the same Connection object.
pp
and
• Reduces network calls between the application
the database.
• Disable the autoauto-commit mode so that you can
rollback the transaction.
Batch Updates
con.setAutoCommit(false);
Statement stmt=con.createStatement( );
stmt.addBatch(“INSERT
(
INTO p
product
(p_id, p_desc) VALUES (1001,’Printer ’ ) ” );
stmt.addBatch(“INSERT
stmt.addBatch( INSERT INTO product
(p_id, p_desc) VALUES (1002,’Scanner’ ) ”
);
int[ ] count=stmt.executeBatch( ) ;
Metadata
• It gives the information about the data such
as structure and properties of the table.
• JDBC API provides the following two
metadata interfaces to retrieve the
information about the data base and result
set
¾ DatabaseMetaData
D b M D
iinterface
f
¾ ResultSetMetaData interface
DatabaseMetaData
• Provides the methods that enable you to determine
the properties of a database.
• Provides information such as:
¾ Names of database tables
¾ Database version
• Use the following method call to create an object
of the DatabaseMetaData interface:
DatabaseMetaData dbmd=con.getMetaData( );
Methods of DatabaseMetaData
• String
g getDriverName(
g
()
Retrieves the name of the JDBC driver
g getDriverVersion(
g
()
• String
Retrieves the version of the JDBC driver
• String getURL( )
Retrieves the URL of the database.
• boolean isReadOnly( )
Indicates whether the database is read only
database
ResultSet MetaData
•A ResultSetMetaData is an object that can be
used to get information about the properties of
the columns in a ResultSet object.
•Provides information such as:
¾ Number of columns
¾ Names of columns
¾ Data types of the columns
•ResultSetMetaData rsmd=rs.getMetaData(
g
( );
Methods of ResultSetMetaData
•
•
•
•
•
•
int getColumnCount( )
String getColumnName(int column_index)
S i getTableName(int
String
T bl N
(i column_index)
l
i d )
int getColumnType(int column_index)
boolean isCaseSensitive(int column_index)
boolean isReadOnly(int column
column_index)
index)
Row Sets
• RowSet interface extends the ResultSet
interface.
• Row sets don’t have to be tied to a database
connection.
• Some of the interfaces that extend the
RowSet interface:
¾ CachedRowSet
¾ WebRowSet
¾ FilteredRowSet and JoinRowSet
¾ JdbcRowSet
Jdb R S
Cached Row Sets
• Contains all data from a result set.
• Each user command simply opens the
database connection, issues a query ,puts
the result in a row set and then closes the
database connection.
• You can also modify the data in a cached
row set.
• You need to make an explicit request to
accept the accumulated changes.
• Not appropriate for large query results.
• ResultSet rs=stmt.executeQuery(str);
CachedRowSet rowset=new
com.sun.rowset.CachedRowSetImpl(
C h dR S I l( ));
rowset.populate(rs);
con.close(
l ( ));
• rowset.acceptChanges(con);
OR
• rowset.setURL(“….”);
rowset setUsername(“…”);
rowset.setUsername(
);
rowset.setPassword(“……”);
rowset.setcommand(“SELECT
rowset.setcommand( SELECT * FROM Books
Books”);
);
rowset.execute( );
• rowset.acceptChanges( );
JDBC Class Diagram