Jdbc

JDBC

Jussi
Pohjolainen

Tampere
University
of
Applied
Sciences

JDBC
Intro

•  Java
Database
Connec@vity
in
Java
since
1.1

•  API
in
Java
for
accessing
Databases

•  PlaDorm
independent,
Database
independent

Drivers

•  To
access
a
database,
you
need
a
driver

•  To
code
in
Java
is
always
the
same,
changing

the
driver
changes
the
connec@on
to
diﬀerent

database.

•  Lot’s
of
drivers
for
diﬀerent
databases:

MySQL,
Text,
MS
SQL
Server..

Driver
Types

•  JDBC
Drivers
are
divided
into
four
categories

–  Type
1
that
calls
na@ve
code
of
the
locally
available
ODBC

driver.

–  Type
2
that
calls
database
vendor
na.ve
library
on
a
client
side.

–  Type
3,
the
pure-‐java
driver
that
talks
with
the
server-‐side

middleware
that
then
talks
to
database.

–  Type
4,
the
pure-‐java
driver
that
uses
database
na@ve
protocol.

•  In
most
cases
you
can
access
the
same
database
with
four

diﬀerent
type
of
drivers

•  List
of
drivers:

–  hQp://developers.sun.com/product/jdbc/drivers

To
use
JDBC

1.  Register
driver

2.  Access
database

3.  Do
some
SQL
magic

4.  Handle
result

5.  Close
the
connec@on

1.
Register
the
Driver

try {
// The driver string here is given you by the
// driver documentation.
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
}
catch(ClassNotFoundException e) {
System.out.println(”Can’t find the driver!");
}

2.
Connect
to
Database

try {
Class.forName ("sun.jdbc.odbc.JdbcOdbcDriver");
Connection conn = DriverManager.getConnection(
"jdbc:odbc:mydatabasename", ”userlogin", ”password");
}
catch(SQLException e) {

}

}

3.
Some
SQL
Magic

try {

Statement statement = conn.createStatement();
statement.executeUpdate("DELETE FROM employees WHERE id<20");

}
catch(SQLException e) { }
catch(ClassNotFoundException e) { }

5.
Close
connec@on

try {

statement.executeUpdate("DELETE FROM employees WHERE id<20");

statement.close();
conn.close();
}
catch(SQLException e) { }
catch(ClassNotFoundException e) { }

Handle
Result?

•  In
previous
example,
the
result
of
the
SQL
was

boolean
value
(we
did
not
handle
it).

•  If
SQL
is
select,
then
you
can
retrieve
the

results

•  Use
ResultSet
object.
ResultSet
holds
the

result
of
your
SQL
query

•  You
can
navigate
in
result
set

4.
Handling
Results

try {

ResultSet rs = statement.executeQuery("SELECT * FROM employees");

while(rs.next()) {
System.out.println(rs.getString("someColumn"));
}

statement.close();
conn.close();
}
catch(SQLException e) {
}

}

ResultSet

rs.next();

rs.next();

rs.next();

//
Prints
“Williams”

System.out.println(rs.getString(“Last
Name”));

ResultSetMetaData

•  Don’t
know
column
names?
Or
amount?

•  You
can
check
these
using
ResultSetMetaData

•  Example
usage:

ResultSetMetaData rsmd = rs.getMetaData();
int numCols = rsmd.getColumnCount ();

while (rs.next()) {
for (int i=1; i<=numCols; i++) {
System.out.println(rs.getString(i));
}
}

Transac@ons

•  If
you
want
to
commit
several
sql
–
commands

into
one:

–  conn.setAutoCommit(false);
–  // do some sql
–  conn.commit();
–  conn.rollback();

Prepared
Statements

•  Prepared
statement
or
parameterized

statement
is
a
feature
used
to
execute
the
same

or
similar
database
statements
repeatedly
with

high
eﬃciency.

•  Example

Connection con = connect();
String sql = "UPDATE table1 set one = ?, two = ?";
PreparedStatement preStmt = con.prepareStatement(sql);
preStmt.setInt(1, 123);
preStmt.setString(2, "myNewValue2");
preStmt.executeUpdate();

Scrollable
Resultset

Statement stmt =
con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);

ResultSet srs = stmt.executeQuery(SQLQuery);

Values

•  TYPE_FORWARD_ONLY
(default)

•  TYPE_SCROLL_INSENSITIVE

•  TYPE_SCROLL_SENSITIVE
–
all
updates

happens
immediately

•  CONCUR_READONLY

•  CONCUR_UPDATABLE

Methods
for
Scrollable
ResultSet

•  next()

•  previous()

•  beforeFirst()

•  aierLast()

•  absolute(int
x)

Update
Result

•  It’s
possible
to
update
the
result
using

methods

–  updateString()

–  updateInt()

–  updateFloat()..

•  Once
updated,
call
updateRow(),
which
will

move
the
result
to
database

Update

while(rs.next()){
System.out.println(rs.getString("Firstname"));
}

rs.previous();
rs.updateString("Firstname", args[0]);
rs.updateRow();

Adding
a
Row

rs.moveToInsertRow();
rs.updateString("firstname", "Jack");
rs.updateString("lastname", "Smith");
rs.updateInt("idnumber", 20);
rs.insertRow();

Dele@ng
a
Row

•  rs.last();
•  rs.deleteRow();

Jdbc

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