Concise way to learn JDBC

1. JAVA DATABASE CONNECTIVITY
A vendor neutral way to talk to database
By
Atul Saurabh
Assist. Professor
Babaria Institute of Technology

2. THE DATABASE
A database is an organized collection of data.
-Wikipedia
a)
A file contains data in sequential form. Whenever we need
to retrieve data from a file, we need to traverse the file
character by character.
b)
There is no natural way to establish relation between file
even though we can distribute data in different files.
c)
There is no effective way to check whether there is any
redundancy in the file.
d)
There is no effective way to check the integrity of the data
in a file.

3. FORMS OF DATABASES
On the basis of organization of data, database appears
in different forms
a)
Relational Database : The data is organized in form
of relations or tables. E.g. Oracle, MySQL, SyBase,
Postgres etc.
b)
Hierarchal Database : The data is organized in
some tree form. E.g. XML, LDAP ect.
c)
Object Oriented Database : The data is
encapsulated in form of object. Each object
represent a row from some table in other kind of
database. E.g. Java Persistence API, Hibernate etc.

4. TALKING TO THE DATABASE
Each database vendor follows their own protocols for
managing data inside database. Though the same
syntax i.e. SQL is followed by every database vendor,
their internal representation of data, i.e. datatype, is
different. As for example MySQL uses float for floating
type number but Oracle uses number(m,n) for the
same.
Programming language like Java provides its own
syntax and datatypes.
These diversities simply put a requirement of a layer
which translate programming language representation
into vendor specific representation. This layer is
commonly known as database driver.

5. PREREQUISITES FOR DATABASE CONNECTION
Whenever a database is connected through some
programming language following information is
required:
1)
The driver class
2)
Authentication credentials for database engine
3)
The URL to locate the database.

6. STEPS TO CONNECT DATABASE THROUGH
JAVA
1)
Installation of vendor specific driver : Normally
drivers comes in form of JAR file. Here are the
names of some drivers
a) ORACLE : oracle.jdbc.driver.OracleDriver
b) MySQL : com.mysql.jdbc.Driver
c) Postgres : org.postgresql.Driver
d) ODBC
: sun.jdbc.odbc.JdbcOdbcDriver
There are three ways to install JDBC driver.
i) Create a lib folder inside the project folder and
place the JDBC driver JAR file inside lib and set
classpath using manifest file.

7. ii) CLASSPATH : set class path. Follow the steps :
Create any directory inside the system say in D: drive
create a directory with name library. Put the JAR file
inside this folder. Let the name of jar is mysqlconnector-java-5.0.8-bin.jar. Now
Go to
My Computer
|--Properties
|---Advanced System Setting
|------Environmental Variable
|---- User Variable
|-----New
The following windows appears :

8. In variable name write
CLASSPATH
In variable value write
D:library mysql-connector-java-5.0.8-bin.jar;
.
(Mind the last . (dot) after semi-colon)
iii)
Place
your
JAR
%JAVA_HOME%/jre/lib/ext directory.
file
If ODBC driver is used then no need to install the
driver. Skip this step
inside

9. 2) Instantiate the driver : To instantiate the driver
following code can be used
class DatabaseConnection
{
public void makeConnection()
{
try
{
String
driverClass=“sun.jdbc.odbc.JdbcOdbcDriver”
Class.forName(driverClass);
}
catch(ClassNotFoundException e)
{
Logger.getLogger(DatabaseConnection.class.getName()).l
og(Logger.SEVER,”The Driver Class Is Not Located”,e);
}
}

10. 3) Establish the connection : Use DriverManager to establish the
connection:
public class DatabaseConnection
{
public void makeConnection()
{
try {
String driverClass=“sun.jdbc.odbc.JdbcOdbcDriver”
String username=“”;
String passwd=“”;
String url=“jdbc:odbc:dsn”;
Class.forName(driverClass);
Connection c=DriverManager.getConnection(url,username,passwd);
if(!c.isClosed())
System.out.println(“Connection established”);
}
catch(ClassNotFoundException e) {
Logger.getLogger(DatabaseConnection.class.getName()).log(Logger.SEVER,
”The Driver Class Is Not Located”,e);
}
catch(SQLException sqle){
Logger.getLogger(DatabaseConnection.class.getName()).log(Logger.SEVER,
”Unable To Connect”,sqle);
}
}
}

11. CREATING A DSN
DSN stands for Data Source Name. It is required only if
we are using ODBC driver. To create a DSN use the
following steps :
Go To
Control Panel
|----Administrative Tool
|--- Data Source
And create a System DSN by supplying the DSN name
and selecting the database.

12. ARCHITECTURE OF JDBC

13. TYPES OF JDBC DRIVERS
Type 1: JDBC-ODBC Bridge Driver:
In a Type 1 driver, a JDBC bridge is used to access ODBC
drivers installed on each client machine. Using ODBC
requires configuring on your system a Data Source Name
(DSN) that represents the target database.

14. Type 2: JDBC-Native API:
In a Type 2 driver, JDBC API calls are converted into
native C/C++ API calls which are unique to the database.
These drivers typically provided by the database vendors
and used in the same manner as the JDBC-ODBC Bridge,
the vendor-specific driver must be installed on each
client machine.

15. Type 3: JDBC-Net pure Java :
In a Type 3 driver, a three-tier approach is used to
accessing databases. The JDBC clients use standard
network sockets to communicate with an middleware
application server. The socket information is then
translated by the middleware application server into the
call format required by the DBMS, and forwarded to the
database server.

16. Type 4: 100% pure Java:
In a Type 4 driver, a pure Java-based driver that
communicates directly with vendor's database through
socket connection. This is the highest performance driver
available for the database and is usually provided by the
vendor itself.

17. SQL DATA TYPE AND CORRESPONDING
JAVA TYPES
Sl. No.
SQL Data Type
Java Data Type
1
INTEGER, INT
int
2
SMALLINT
short
3
NUMERIC(m,n),
DECIMAL(m,n),
DEC(m,n)
java.math.BigDecimal
4
FLOAT(n)
double
5
REAL
float
6
CHARACTER(n),
CHAR(n)
String
7
VARCHAR(n)
String

18. Sl. No.
SQL Data Type
Java Data Type
8
BOOLEAN
Boolean
9
DATE
java.sql.Date
10
TIME
java.sql.Time
11
TIMESTAMP
java.sql.Timestamp
12
BLOB
java.sql.Blob
13
CLOB
java.sql.Clob
14
ARRAY
java.sql.Array

19. EXECUTING SQL QUERY
In native SQL there are two types of queries
a)
The query which changes the values in one or more
rows possibly by creating or deleting rows. E.g.
INSERT, UPDATE, DELETE and ALTER.
b)
The query which simply returns the projection of one
or more tables. E.g. SELECT.
Whenever we execute query (a) then the query always
returns us how many rows get affected.
Whenever we execute query (b) we get a snapshot of
subset original table(s). This snapshot is commonly
known as ResultSet.

20. The java.sql.Connection
The Connection object represents a connection to the
database.
i) Statement createStatement() : This method is used to
get the Statement object
The java.sql.Statement
The Statement object is used to execute a native SQL
queries.
i)
ResultSet executeQuery(String query) : This method
is used to execute query (b).
ii)
int executeUpdate(String query) : Used to execute
query (a).
iii)
Int getUpdateCount() : Returns the number of records
affected by previous update query.

21. The java.sql.ResultSet
The ResultSet is a snapshot of subset of original tables(s) .
A ResultSet is always provided by a cursor.
Initially cursor is pointed outside the table. We can
visualize ResultSet as follows
Col1
Col2
….
Coln
R01
R02
….
R0n
R11
R12
....
R1n
R21
R22
….
R2n

22. i)
boolean next() : This method moves the cursor one
row downward and returns true if there is any row
available below the cursor.
ii)
Xxx getXxx(int colNumber) : This method returns the
values inside the column represented by colNumber.

23. AN EXAMPLE
public class InsertQueryExample
{
public static void main(String [] args)
{
try
{
String driverClass=“sun.jdbc.odbc.JdbcOdbcDriver”;
String url=“jdbc:odbc:dsn”;
String uname=“”;
String upass=“”;
Class.forName(driverClass);
Connection c=DriverManager.getConnection(url,uname,upass);
String query=“insert into db values(null,’atul’,’assist. Prof’);
Statement s=c.createStatement();
int res=s.executeUpdate(s);
if(res > 0)
System.out.println(“Values inserted successfully”);
}
catch(Exception e)
{
}
}
}

24. SECOND EXAMPLE
import java.sql.*;
public class SelectQueryExample
{
public static void main(String [] args)
{
try
{
Connection c= getConnection();
Statement stmt=c.createStatement();
String query=“select * from student”;
ResultSet rs=stmt.executeQuery(query);
while(rs.next())
{
System.out.println(“Student Id=“+rs.getInt(1));
System.out.println(“Student Name=“+rs.getString(2));
}
}
catch(Exception e)
{
e.printStackTrace();
}
}
}

25. EFFECT OF NEXT() OPERATION
The next() method of ResultSet makes the cursor
forward. If the cursor is at the last row this method
returns false. Suppose the initial condition of
ResultSet is as follows
Col1
Col2
…
ColN
R00
R01
…
R0N
R10
R11
…
R1N
R20
R21
…
R2N

26. Now if we fire next() then the cursor moves forward
and the method returns true as the cursor pointing to
the first row.
Col1
Col2
…
ColN
R00
R01
…
R0N
R10
R11
…
R1N
R20
R21
…
R2N

27. Now if the cursor points to the last row then the next()
method returns false and cursor will not move forward.
Col1
Col2
…
C olN
R00
R01
…
R0N
R10
R11
…
R1N
R20
R21
…
R2N

28. IS THERE ANY METHOD PREVIOUS()?
The next() method of ResultSet moves the cursor one
row forward. The ResultSet interface defines the
following method to manipulate data retrieval from the
ResultSet.
1)
boolean previous() : Move the cursor one row
backward. If the cursor is pointing above the first
row, the method returns false.
2)
boolean first() : Move the cursor to the first row.
3)
boolean last() : Move the cursor to the last row.
4)
boolean relative(int n) : Moves the cursor to the
location n from the current position.

29. PROBLEMS WITH STATEMENT
Commonly we use java.sql.Statement interface to
execute sql queries. Here is a typical example of SQL
insert query
String
query=“insert
values(null,‟Atul‟,‟Vadodara‟)”;
into
student
Statement s=con.createStatement();
s.executeUpdate(query);
There are two major problems with this statement:
1) If we need to change the values then query will be
reconstructed and placed at different memory location.
Here is a typical memory layout for this scheme:

30. insert into student values(null,’Atul’,’Vadodara’)
0x3356FF9
The first query
insert into student values(null,’Prakash’,’Delhi’)
0x3356A80
The second query only value changed
2) We need to care about the quotes („). That means
values must be wrapped by quotes if the SQL syntax
requires that.
These two limitations makes Statement a less preferable
choice for programmers.

31. THE PREPAREDSTATEMENT
To avoid the complexity of Statement, Java provides another
interface called PreparedStatement
Here is a typical way to execute a insert query using
PreparedStatement.
String query=“insert into student values(null,?,?)”;
PreparedStatement p=con.prepareStatement(query);
p.setString(1,”Atul”);
p.setString(2,”Vadodara”);
p.executeUpdate();
Look at the query: instead of placing values a ? Is placed.
The ? is called positional parameter. The first ? is numbered
1, the second ? is numbered 2 and so on.

32. The values of each ? can be set using setXxx(int pos,
Xxx value);
Note: Xxx will be replaced by String, Int, Double, Float
ect. depending upon what datatype is used for the
position.
Second point : When we are setting the value of each ?
we are not taking care of quotes(„). The quotes will be
automatically wrapped by PreparedStatement.
When we supply any query to PreparedStatement then
instead of wasting memory, it just leave the blank space
for each ?. Now if we require to change the value only
blank space if filled with new values.

33. insert into student values(null,
________________,
________________
)
0x3356A79
Memory allocation for query by PreparedStatement
insert into student values(null, ‘Atul’,’Vadodara’)
0x3356A79
Query after setting the value

34. insert into student values(null, ‘Prakash’,’Delhi’)
0x3356A79
Query after changing the value.
Note that the memory location of the query remains
same and quotes are added.

35. SCROLLABLE RESULTSET
PreparedStatement gives us a very efficient way to create
precompiled (in terms of java only) queries. Memory
wastage and notorious quote problem are solved by it.
The PreparedStatement was introduced in Java 1.1. At
that time there is no way by which we can move backward
or jump at any location in ResultSet.
After the introduction of JDBC 2 the ResultSet is now
scrollable. That means the cursor can move both
backward and forward or jump to specific location in the
ResultSet. By default, the ResultSet in not scrollable.
That means
Connection c=…..;
String query=“select * from table”;
PreparedStatement p=c.prepareStatement(query);
ResultSet rs=p.executeQuery(); // oops rs is not scrollable

36. HOW TO MAKE RESULTSET SCROLLABLE
To make a ResultSet scrollable we need to use the
following method to get PreparedStatement object.
PreparedStatement prepareStatement(String query, int
type, int concurrency);
This method is defined in java.sql.Connection interface.
The type parameter may have following values:
Allowed values for type
purpose
ResultSet.TYPE_FORWARD_ONLY
The resultset is not
scrollable
ResultSet.TYPE_SCROLL_INSENSITIVE
The resultset is
scrollable but not
sensitive to
database change
ResultSet.TYPE_SCROLL_SENSITIVE
The resultset
scrollable and
sensitive to
database change

37. The concurrency parameter may have following values:
Allowed values for
concurrency
purpose
ResultSet.CONCUR_READ
_ONLY
The resultset can not be
used to update database
ResultSet.CONCUR_UPDA
TABLE
The resultset can be used
to update database.
Connection c=……;
String query=“select * from table”;
PreparedStatement
p=c.prepareStatement(query,ResultSet.TYPE_SCROLL_IN
SENSITIVE,ResultSet.CONCUR_READ_ONLY);
ResultSet rs=p.executeQuery(); // OK rs is scrollable but
not updatable

38. METHOD FOR SCROLLING RESULTSET
To traverse back and forth in ResultSet JDBC API
provides the following methods :
1) boolean previous() : Move the cursor one row
backward. If the cursor is pointing above the first row,
the method returns false.
2) boolean first() : Move the cursor to the first row.
3) boolean last() : Move the cursor to the last row.
4) boolean relative(int n) : Moves the cursor to the
location n from the current position.
5) void beforeFirst() : move the cursor before the first
row.
6) void afterLast() : move the cursor after the last row.
7) isBeforeFirst()
8) isAfterLast():
Test whether the cursor is before the first row or the last
row.

39. UPDATABLE RESULTSET
ResultSet is normally a memory snapshot of subset of
tables present inside the database and is a result of Select
query. Generally it is used only for data retrieval. But
sometimes while traversing the ResultSet we need to make
changes in our database.
By default a ResultSet is neither scrollable nor updatable.
That simply imply that we can not use a ResultSet to make
change in database. After the introduction of JDBC 2,
ResultSet can be made scrollable as well as updatable.
To make a ResultSet updatable we need to obtain ResultSet
as follows:
Connection c=……;
String query=“select * from table”;
PreparedStatement
p=c.prepareStatement(query,ResultSet.TYPE_SCROLL_INS
ENSITIVE,ResultSet.CONCUR_UPDATABLE);
ResultSet rs=p.executeQuery(); // OK rs is scrollable and
updatable

40. MOVING FORWARD AND BACKWARD
Connection c=……;
String query=“select * from table”;
PreparedStatement
p=c.prepareStatement(query,ResultSet.TYPE_SCROLL
_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
ResultSet rs=p.executeQuery();
rs.next(); // Move the cursor to first row
rs.next(); // Move the cursor to second row
rs.previous(); // Move the cursor to first row again
rs.last(); // place the cursor to last row

41. Col1
…
ColN
R00
R01
…
R0N
R10
R11
…
R1N
.
.
…
.
RM0

Col2
RM1
…
RMN
Effect of 2 next() operation
Col1
Col2
…
ColN
R00
R01
…
R0N
R10
R11
…
R1N
.
.
.
.
RM0
RM1
…
RMN

42. 
Effect of one previous() operation
Col1
Col2
…
ColN
R00
R01
…
R0N
R10
R11
…
R1N
.
.
.
.
RM0
RM1
…
RMN

43. UPDATING CURRENT ROW VALUES
Connection c=……;
String query=“select * from table”;
PreparedStatement
p=c.prepareStatement(query,ResultSet.TYPE_SCROLL
_INSENSITIVE,ResultSet.CONCUR_UPDATABLE);
ResultSet rs=p.executeQuery();
rs.next(); // Move the cursor to first row
rs.next(); // Move the cursor to second row
rs.updateString(2,”Prakash”); // Changing the value of
2nd column of 2nd row
rs.updateRow(); // Making effect permanent.

44. 
Initial Value
Col1
…
ColN
R00
R01
…
R0N
R10
R11
…
R1N
.
.
.
.
RM0

Col2
RM1
…
RMN
Effect of updateXxx and updateRow(see prev example)
Col1
Col2
…
ColN
R00
R01
…
R0N
R10
Prakash
…
R1N
.
.
.
.
RM0
RM1
…
RMN

45. INSERTING NEW VALUES
Connection c=……;
String query=“select * from table”;
PreparedStatement
p=c.prepareStatement(query,ResultSet.TYPE_SCROLL_INSENSITI
VE,ResultSet.CONCUR_UPDATABLE);
ResultSet rs=p.executeQuery();
rs.next(); // Move the cursor to first row
rs.next(); // Move the cursor to second row
String id=0;
String name=“Dinesh”;
int age=25;
String gender-”Male”;
rs.moveToInsertRow(); // Move To the Row where insertion is
done
rs.updateInt(1,id); // update first column
rs.updateString(2,name); // update second column
rs.updateInt(3,age); // update third column
rs.updateString(4,gender); // update fourth column
rs.insertRow(); // make the effect permanent
rs.moveToCurrentRow(); // move to second row

46. Col1
Col2
…
ColN
R00
R01
…
R0N
R10
R11
…
R1N
.
.
.
.
RM0
RM1
…
R(M=1 R(M+1 …
))
)1
RMN
Insert Row
Cursor moved to insert row
Cursor moved back
Col1
Col2
…
ColN
R00
R01
…
R0N
R10
R11
…
R1N
.
.
.
.
RM0
RM1
…
RMN
R(M+1)0
R(M+1)1
…
R(M+1)N
Merged
R(M+1
)N

47. UPDATABLE METHODS SUMMARY
All the update related methods are defined in
java.sql.ResultSet interface.
1)
void moveToInsertRow() : moves the cursor to insert
row. The insert row is a special row for inserting new
data with updateXXX and insertRow methods.
2)
void moveToCurrentRow(): move the cursor back
from the insert row to the row that is occupied when
moveToInsertRow method was called.
3)
void insertRow(): insert the content of the insert row
into the database and resultset.
4)
void updateXxx(int colnumber,Xxx data) : update the
field in the current row of the resultset.
5)
void updateRow(): sends the current row updates to
the database.

48. METADATA
In SQL, data that describe the database or one of its
parts are called metadata. In general, metadata gives
the following information
1)
2)
3)
4)
5)
What is the structure of a database?
How many maximum connection that can be
established concurrently to the database?
How many rows are there in a table?
How many columns a table has?
Is ResultSet Scrollable or updatable ?
There are some other advanced information we can
collect from the metadata.
These information, in general, are not required for
application programmers. But these information are
highly required for those who want to design
advanced tools for database.

49. TYPES OF METADATA
On the basic of source of metadata, it is categorized
into three types
1)
Database Metadata
database itself.
:
The
information
about
2)
ResultSet Metadata : The information about the
ResultSet.
3)
PreparedStatement parameter: The information
about the parameters of prepared statement.