1. Java Database Connectivity: JDBC
Representation and Management of Data on the Internet

2. Database Connectivity
Relational databases
Manage all information generated by businesses
Centric to business applications
Established and Mature
Application developers require standard interface to relational databases
Change in database vendor should not require change in application programs

3. Relational Database Properties
Fundamental Properties
Tables, Indexes, Triggers, Stored Procedures, Transactions
ACID Properties – Atomicity, Consistency, Isolation, Durability
Data Definition (DDL)
Manage Database Objects
For example, Create and delete tables, indexes, stored procs
Queries (DML)
Read, write, or delete information between one or more related tables
SQL

4. ACID Properties Atomic Consistent Isolated Durable
Updates in a transaction either occur or don’t occur
Consistent
Transaction always preserves the system state
Isolated
Concurrent transactions occur as if occurring in isolation (there is no partial view of another transaction)
Durable
Committed transactions survive failures of any type (e.g., communication, server). Transaction logging allows recovery.

5. SQL Statements (DML) Insert Update Delete Select
INSERT into Course(CourseID, Name, ProfessorID)
values (162, ‘Java101’, 12);
Update
UPDATE Course set NumStudents = 0;
Delete
DELETE from Course where (ProfessorID = 100 );
Select
SELECT Name from Course where CourseID = 162;

6. Relational DBs and Objects
Persistent objects must be mapped to relation tables
Relation Tables
Class Diagram
Professor
ProfID
Name
Course
CourseID
ProfID
Name
Location
Time
Student
StudentID
Name
BillingInfo
0..*
Student
Course
prereq
1..* 1
teaches
Professor
takes
Prereq
CourseID
PrereqCourseID
Takes
StudentID
CourseID

7. What is JDBC?
A pure Java API for database communication similar to ODBC (JDBC created in 1995)
JDBC and ODBC are based on the same standard: X/Open's SQL Call-Level Interface
A set of classes that perform database transactions
Connect to relational databases
Send SQL commands
Process results
JDBC2 has been defined (part of Java 2 in 1998)
NOT universally supported
Additional features such as scrollable cursors, batch updates

8. Benefits of JDBC
No proprietary DB code (although pass- through is supported)
Don’t have to rely on single vendor...ever
Don’t need to make DB vendor decision early
Easier for DB vendors
Don’t need to provide a query language, only implement API
Only low-level support

9. Proprietary, vendor-specific database access protocol
JDBC Architecture
Java Application
JDBC API
JDBC Driver Manager
JDBC Driver API
(T1) JDBC-
ODBC Bridge
(T2) Java Portion
(T3) Java
Client
(T4) Java
Driver to
vendor's
protocol
JDBC Drivers
Native Portion
ODBC Driver
Server
Component
Proprietary, vendor-specific
database access protocol
Provided with
Sun's JDK

10. JDBC Classes java.sql.* provides classes used by an application
<<Interface>>
Statement
<<Singleton>>
<<Interface>>
<<Interface>>
<<Interface>>
DriverManager
Connection
PreparedStatement
ResultSet
<<Interface>>
<<Interface>>
<<Interface>>
DatabaseMetaData
CallableStatement
ResultSetMetaData

11. JDBC Statement Types (2)
Callable Statements
Vendor specific invocation of stored procedures
String sql = “begin ? := Class.registerStudent(?, ?, ?, ?);
CallableStatement stmt = connection.prepareCall(sql);
stmt.registerOutParameter(1, Types.Integer);
stmt.setInt(2, studentID);
stmt.setString(3, classList);
stmt.registerOutParameter(3, OracleTypes.CURSOR);
stmt.registerOutParameter(4, OracleTypes.CURSOR);
stmt.execute();
int numClasses = stmt.getInt(1);
ResultSet classList = stmt.getObject(3);
ResultSet unavailableClassList = stmt.getObject(4); …
classList.close(); Close ALL result sets !!!
unavailableClassList .close();
stmt.close();

12. Result Sets Contain rows from query results
ResultSet maintains the current row
Can obtain an item from any column in the current row
Can move forward, not backward
Greatly enhanced in JDBC 2.0 (Java 2)
Scrollable move forward and backward
Updatable write through the ResultSet to the database
Batch Updates - submit multiple update statements for performance improvement
RowSets - disconnect then reconnect to Database using optimistic concurrency control
Others Features - Connection Pooling, JNDI Naming

13. Statement SQL Insert Update Delete
String insertStmt = "INSERT into Course(CourseID, Name, ProfessorID) " +"values (162, ‘Java101’, 12)";
stmt.executeUpdate(insertStmt);
Update
String depositStmt = "UPDATE Course set NumStudents = 0";
stmt.executeUpdate(depositStmt);
Delete
String deleteStmt = "DELETE from Course where (ProfessorID = " + terminatedProfessor + ”)";
stmt.executeUpdate(deleteStmt);

14. Example - Schema
Assume the tables shown below. Write a program that displays all the students and the courses they take.

15. JDBC Summary Three Statement Types Basic Steps
Statement – simplest, slowest (for repeated calls), Difficult handling of quotes
PreparedStatement – Allows DB to cache parsed SQL
CallableStatement – Executes DB stored Procedure
Basic Steps
Load Driver(s) (typically with Class.forName)
Obtain a connection (DriverManager.getConnection())
Get Statement from connection
connection.createStatement - Statement
connection.prepareStatement - PreparedStatement
connection.prepareCall - CallableStatement
stmt.executeQuery , stmt.executeUpdate, or stmt.execute

16. What is ODBC? ODBC is (Open Database Connectivity):
A standard or open application programming interface (API) for accessing a database.
SQL Access Group, chiefly Microsoft, in 1992
By using ODBC statements in a program, you can access files in a number of different databases, including Access, dBase, DB2, Excel, and Text.
It allows programs to use SQL requests that will access databases without having to know the proprietary interfaces to the databases.
ODBC handles the SQL request and converts it into a request the individual database system understands.
Based on the Open Group standard SQL Call-Level Interface

17. More on ODBC You need: the ODBC software, and
a separate module or driver for each database to be accessed. Library that is dynamically connected to the application.
Driver masks the heterogeneity of DBMS operating system and network protocol.
E.g. (Sybase, Windows/NT, Novell driver)

18. ODBC Architecture Application ODBC driver manager Driver
(DBMS/OS/network)
Application issues SQL queries that is independent of everything
Driver manager loads the drivers at the request of the application. Supplied by microsoft. Guararntees some functions for converting name of data items used by application into names used by the dbms, to guarantee correct operation of the driver
Drivers carry out ODBC functions
exceute SQL queries, translating them to adapt to the syntax and semantic of specific products
Return resultrs to application using buffering mechanism
data source is remote DBMS carries out the functions transmitted by client
SQL queries can be specified in a static way or be includd I strings that are generated and executed dynamically -- but you may get compilation errors at execution time if the string is incorrect.
Error codes standardised
Also possible to request transactional commands commit-work and rollback-workbut only on one dbms server (no “PC)
Data Source

19. JDBC Architecture Oracle Java Application JDBC DB2 Network Postgres
Driver
Oracle
Java Application
DB2
Driver
JDBC
DB2
Network
Postgres
Driver
Postgres

20. JDBC Architecture (cont.)
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

21. Introduction to JDBC
JDBC is used for accessing databases from Java applications
Information is transferred from relations to objects and vice-versa
databases optimized for searching/indexing
objects optimized for engineering/flexibility

22. What is JDBC? JDBC is: Java Database Connectivity JDBC:
is a Java API for connecting programs written in Java to the data in relational databases.
consists of a set of classes and interfaces written in the Java programming language.
provides a standard API for tool/database developers and makes it possible to write database applications using a pure Java API.
The standard defined by Sun Microsystems, allowing individual providers to implement and extend the standard with their own JDBC drivers.
JDBC:
establishes a connection with a database
sends SQL statements
processes the results.
JDBC is the standard for portable access to relational databases from within the Java language.
JDBC is based on the X/Open SQL Call Level Interface, and complies with the SQL92 Entry Level standard.
JDBC specifies a set of object-orient programming classes for the programmer to use in building SQL requests. An additional set of classes describes the JDBC driver API. The most common SQL data types, mapped to Java data types, are supported. The API provides for implementation-specific support for transactional requests and the ability to commit or roll back to the beginning of a transaction.

23. JDBC vs ODBC ODBC is used between applications
JDBC is used by Java programmers to connect to databases
With a small "bridge" program, you can use the JDBC interface to access ODBC- accessible databases.
JDBC allows SQL-based database access for EJB persistence and for direct manipulation from CORBA, DJB or other server objects

24. JDBC API
The JDBC API supports both two-tier and three- tier models for database access.
Two-tier model -- a Java applet or application interacts directly with the database.
Three-tier model -- introduces a middle-level server for execution of business logic:
the middle tier to maintain control over data access.
the user can employ an easy-to-use higher-level API which is translated by the middle tier into the appropriate low-level calls.

25. JDBC Architectures Java Application JDBC driver manager DBMS
JDBC/native
bridge
JDBC/ODBC
bridge
JDBC Driver
(DBMS Specific)
JDBC middleware
(various DBMS)
JDBC on a native driver: A java module translates the java calls produced by the jdbc driver manager into a format used by a driver external to the java environment (usually a pre-existing database driver written in the native language of the machine) NOT PORTABLE--native executable code
JDBC/ODBC Bridge an ODBC driver is used instead of a generic database driver. Translates java calls produced by the jdbc driver manager into calls of the odbc protocol, external to the java environment . Need a ODBC driver for the target DBMS NOT PORTABLE --native executable code
Java Middleware server: a Java component responsible for providing the services required for a driver manager , offering lots of targets. Implemented by companies specialising in constructing software gateways PURE JAVA
Java driver: implements in Java, for specific DBMS, the service required by the driver manager. Drivers typically offered by DBMS vendors for their specific products. PURE JAVA
Native driver
(DBMS specific)
ODBC Driver
DBMS

26. The JDBC Steps
1. Importing Packages 2. Registering the JDBC Drivers 3. Opening a Connection to a Database 4. Creating a Statement Object 5. Executing a Query and Returning a Result Set Object 6. Processing the Result Set 7. Closing the Result Set and Statement Objects 8. Closing the Connection

27. Loading the Driver
We can register the Driver indirectly using the Java statement:
Class.forName(“oracle.jdbc.driver.OracleDriver");
Calling Class.forName causes the Driver class to be loaded
When this class is loaded, it automatically
creates an instance of itself
registers this instance with the DriverManager

28. Another Option
Another option is to create an instance of the driver and register it with the Driver Manager:
Driver driver = new oracle.jdbc.OracleDriver();
DriverManager.registerDriver(driver);

29. An Example Registered Drivers Oracle imaginary1 imaginary2
// A driver for imaginary1 Class.forName("ORG.img.imgSQL1.imaginary1Driver"); // A driver for imaginary2 Driver driver = new ORG.img.imgSQL2.imaginary2Driver(); DriverManager.registerDriver(driver); //A driver for oracle Class.forName("oracle.jdbc.driver.OracleDriver");
Oracle
imaginary1
imaginary2
Registered Drivers

30. 1: Importing Packages
// // Program name: LecExample_1a.java // Purpose: Basic selection using prepared statement // //Import packages import java.sql.*; //JDBC packages import java.math.*; import java.io.*; import oracle.jdbc.driver.*;

31. 2: Registering JDBC Drivers
class LecExample_1a {
public static void main (String args []) throws SQLException {
// Load Oracle driver
DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver());

32. Connecting to the Database
Every database is identified by a URL
Given a URL, DriverManager is asked to find the driver that can talk to the corresponding database
DriverManager tries all registered drivers, until a suitable one is found

33. Connecting to the Database
Connection con = DriverManager. getConnection("jdbc.imaginaryDB1");
acceptsURL(“jdbc.imaginaryDB1”)? a r r
imaginary1
Oracle
imaginary2
Registered Drivers
Read more in DriverManager API

34. 3: Opening connection to a Database
//Prompt user for username and password String user; String password; user = readEntry("username: "); password = readEntry("password: "); // Connect to the local database Connection conn = DriverManager.getConnection ", user, password);

35. Interaction with the Database
We use Statement objects in order to
Extract data from the database
Update the database
Three different interfaces are used:
Statement, PreparedStatement, CallableStatement
All are interfaces, thus cannot be instantiated
They are created by the Connection

36. Querying with Statement
String queryStr =
"SELECT * FROM Member " +
"WHERE Lower(Name) = 'harry potter'";
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery(queryStr);
The executeQuery method returns a ResultSet object representing the query result.
Will be discussed later…

37. Changing DB with Statement
String deleteStr =
“DELETE FROM Member " +
"WHERE Lower(Name) = ‘harry potter’";
Statement stmt = con.createStatement();
int delnum = stmt.executeUpdate(deleteStr);
executeUpdate is used for data manipulation: insert, delete, update, create table, etc. (anything other than querying!)
executeUpdate returns the number of rows modified

38. 4. Creating a Statement Object
// Query the hotels table for resort = 'palma nova’ // Please notice the essential trim PreparedStatement pstmt = conn.prepareStatement ("SELECT hotelname, rating FROM hotels WHERE trim(resort) = ?"); pstmt.setString(1, "palma nova");

39. About Prepared Statements
Prepared Statements are used for queries that are executed many times
They are parsed (compiled) by the DBMS only once
Column values can be set after compilation
Instead of values, use ‘?’
Hence, a Prepared Statement is statement that contains placeholders to be substituted later with actual values

40. Querying with PreparedStatement
String queryStr =
"SELECT * FROM Items " +
"WHERE Name = ? and Cost < ?”;
PreparedStatement pstmt = con.prepareStatement(queryStr);
pstmt.setString(1, “t-shirt”);
pstmt.setInt(2, 1000);
ResultSet rs = pstmt.executeQuery();

41. Changing DB with PreparedStatement
String deleteStr =
“DELETE FROM Items " +
"WHERE Name = ? and Cost > ?”;
PreparedStatement pstmt = con.prepareStatement(deleteStr);
pstmt.setString(1, “t-shirt”);
pstmt.setInt(2, 1000);
int delnum = pstmt.executeUpdate();

42. Statements vs. PreparedStatements: Be Careful!
Are these the same? What do they do?
String val = “abc”;
PreparedStatement pstmt = con.prepareStatement(“select * from R where A=?”);
pstmt.setString(1, val);
ResultSet rs = pstmt.executeQuery();
String val = “abc”;
Statement stmt = con.createStatement( );
ResultSet rs = stmt.executeQuery(“select * from R where A=” + val);

43. Statements vs. PreparedStatements: Be Careful!
Will this work?
No!!! A ‘?’ can only be used to represent a column value
WHY?
PreparedStatement pstmt = con.prepareStatement(“select * from ?”);
pstmt.setString(1, myFavoriteTableString);

44. Timeout
Use setQueryTimeOut(int seconds) of Statement to set a timeout for the driver to wait for a statement to be completed
If the operation is not completed in the given time, an SQLException is thrown
What is it good for?

45. 5. Executing a Query, Returning a Result Set Object & 6
5. Executing a Query, Returning a Result Set Object & 6. Processing the Result Set
ResultSet rset = pstmt.executeQuery();
// Print query results while (rset.next()) System.out.println (rset.getString (1)+"
"+ rset.getString(2));

46. 7. Closing the Result Set and Statement Objects 8
7. Closing the Result Set and Statement Objects 8. Closing the Connection
// close the result set, statement, and the connection rset.close(); pstmt.close(); conn.close(); }

47. Mapping Data Types
There are data types specified to SQL that need to be mapped to Java data types if the user expects Java to be able to handle them.
Conversion falls into three categories:
SQL type to Java direct equivalents
SQL INTEGER direct equivalent of Java int data type.
SQL type can be converted to a Java equivalent.
SQL CHAR, VARCHAR, and LONGVARCHAR can all be converted to the Java String data type.
SQL data type is unique and requires a special Java data class object to be created specifically for their SQL equivalent.
SQL DATE converted to the Java Date object that is defined in java.Date especially for this purpose.
SQL Type to Java direct equivalents
Conversion
Certain SQL types have direct equivalents in Java and can be read directly into Java types. E.g. a SQL INTEGER is a direct equivalent of Java int data type.
Several SQL types can be converted to a Java equivalent. E.g., the SQL CHAR, VARCHAR, and LONGVARCHAR can all be converted to the Java String data type.
A few SQL data types are unique and require a special Java data class object to be created specifically for their SQL equivalent. E.g., the SQL DATE is converted to the Java Date object that is defined in java.Date especially for this purpose.

48. ResultSet
A ResultSet provides access to a table of data generated by executing a Statement
Only one ResultSet per Statement can be open at once
The table rows are retrieved in sequence
A ResultSet maintains a cursor pointing to its current row of data
The 'next' method moves the cursor to the next row

49. ResultSet Methods boolean next() void close() activates the next row
the first call to next() activates the first row
returns false if there are no more rows
void close()
disposes of the ResultSet
allows you to re-use the Statement that created it
automatically called by most Statement methods

50. ResultSet Methods Type getType(int columnIndex)
returns the given field as the given type
fields indexed starting at 1 (not 0)
Type getType(String columnName)
same, but uses name of field
less efficient
int findColumn(String columnName)
looks up column index given column name

51. ResultSet Methods String getString(int columnIndex)
boolean getBoolean(int columnIndex)
byte getByte(int columnIndex)
short getShort(int columnIndex)
int getInt(int columnIndex)
long getLong(int columnIndex)
float getFloat(int columnIndex)
double getDouble(int columnIndex)
Date getDate(int columnIndex)
Time getTime(int columnIndex)
Timestamp getTimestamp(int columnIndex)

52. ResultSet Methods String getString(String columnName)
boolean getBoolean(String columnName)
byte getByte(String columnName)
short getShort(String columnName)
int getInt(String columnName)
long getLong(String columnName)
float getFloat(String columnName)
double getDouble(String columnName)
Date getDate(String columnName)
Time getTime(String columnName)
Timestamp getTimestamp(String columnName)

53. ResultSet Example
Statement stmt = con.createStatement(); ResultSet rs = stmt. executeQuery("select name,age from Employees"); // Print the result while(rs.next()) { System.out.print(rs.getString(1) + ”:“); System.out.println(rs.getShort(“age”)+”“); }

54. Null Values In SQL, NULL means the field is empty
Not the same as 0 or “”
In JDBC, you must explicitly ask if a field is null by calling ResultSet.isNull(column)
For example, getInt(column) will return 0 if the value is either 0 or null!!

55. Null Values
When inserting null values into placeholders of Prepared Statements:
Use the method setNull(index, sqlType) for primitive types (e.g. INTEGER, REAL);
You may also use the setXXX(index, null) for object types (e.g. STRING, DATE).

56. ResultSet Meta-Data
A ResultSetMetaData is an object that can be used to get information about the properties of the columns in a ResultSet object.
An example: write the columns of the result set
ResultSetMetaData rsmd = rs.getMetaData();
int numcols = rsmd.getColumnCount();
for (int i = 1 ; i <= numcols; i++) {
System.out.print(rsmd.getColumnLabel(i)+” “); }
Many more methods in the ResultSetMetaData API

57. Database Time Times in SQL are notoriously non-standard
Java defines three classes to help
java.sql.Date
year, month, day
java.sql.Time
hours, minutes, seconds
java.sql.Timestamp
year, month, day, hours, minutes, seconds, nanoseconds
usually use this one

58. Cleaning Up After Yourself
Remember to close the Connections, Statements, PreparedStatements and ResultSets
con.close();
stmt.close();
pstmt.close();
rs.close()

59. Dealing With Exceptions
An exception can have more exceptions in it.
catch (SQLException e) {
while (e != null) {
System.out.println(e.getSQLState());
System.out.println(e.getMessage());
System.out.println(e.getErrorCode());
e = e.getNextException(); }

60. LOBs: Large OBjects Two types:
CLOB: Character large object (a lot of characters)
BLOB: Binary large object (a lot of bytes)
Actual data is not stored in the table with the CLOB/BLOB column. Only a pointer to the data is stored there
I will show how to use a BLOB; CLOBs are similar

61. Retrieving a BLOB create table userImages( user varchar(50),
image BLOB );
ResultSet rs =
stmt.executeQuery(“select image from userImages”);
while (rs.next) {
Blob b = rs.getBlob(“image”);
InputStream stream = b.getBinaryStream();
doSomething(stream); }

62. Inserting a BLOB PreparedStatement pstmt =
con.prepareStatement(“insert into userImages values(‘snoopy’, ?)”);
File file = new File(“snoopy.jpg”);
InputStream fin = new FileInputStream(file);
pstmt.setBinaryStream (1, fin, file.length());
pstmt.executeUpdate();

63. Transactions and JDBC
Transaction = more than one statement which must all succeed (or all fail) together
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 = abort

64. What happens if this update fails?
Example
Suppose we want to transfer money from bank account 13 to account 72:
PreparedStatement pstmt = con.prepareStatement(“update BankAccount
set amount = amount + ?
where accountId = ?”);
pstmt.setInt(1,-100);
pstmt.setInt(2, 13);
pstmt.executeUpdate();
pstmt.setInt(1, 100);
pstmt.setInt(2, 72);
What happens if this update fails?

65. Transaction Management
Transactions are not explicitly opened and closed
The connection has a state called AutoCommit mode
if AutoCommit is true, then every statement is automatically committed
if AutoCommit is false, then every statement is added to an ongoing transaction
Default: true

66. AutoCommit setAutoCommit(boolean val)
If you set AutoCommit to false, you must explicitly commit or rollback the transaction using Connection.commit() and Connection.rollback()
In order to work with LOBs, you usually have to set AutoCommit to false, while retrieving the data
Note: DDL statements in a transaction may be ignored or may cause a commit to occur. The behavior is DBMS dependent
Lobs and DDL

67. Fixed Example con.setAutoCommit(false); try {
PreparedStatement pstmt = con.prepareStatement(“update BankAccount
set amount = amount + ?
where accountId = ?”);
pstmt.setInt(1,-100); pstmt.setInt(2, 13);
pstmt.executeUpdate();
pstmt.setInt(1, 100); pstmt.setInt(2, 72);
con.commit();
catch (Exception e) {
con.rollback(); }

68. Isolation Levels
How do different transactions interact? Do they see what another has written?
Possible problems:
Dirty Reads: a transaction may read uncommitted data
Unrepeatable Reads: two different results are seen when reading a tuple twice in the same transaction
Phantom Reads: tuples are added to a table between two readings of this table in a single transaction

69. JDBC defines four isolation modes:
Isolation Levels
JDBC defines four isolation modes:
Level
Dirty Read
Unrepeatable Read
Phantom Read
Read Uncommited
Yes
Read Commited No
Repeatable Read
Serializable

70. Isolation Levels
Set the transaction mode using setTransactionIsolation() of class Connection
Oracle only implements:
TRANSACTION_SERIALIZABLE
An exception may be thrown if serializability isn’t possible
TRANSACTION_READ_COMMITED
This is the default

71. Level: READ_COMMITED 1 2 Transaction 1: insert into A values(1)
select * from A
Question: Is it possible for a transaction to see 1 in A, but not 2?
Question: Is it possible for the 2 queries to give different answers for level SERIALIZABLE? 1 2
Table: A

72. Mapping Java Types to SQL Types
SQL type Java Type CHAR, VARCHAR, LONGVARCHAR String NUMERIC, DECIMAL java.math.BigDecimal BIT boolean TINYINT byte SMALLINT short INTEGER int BIGINT long REAL float FLOAT, DOUBLE double BINARY, VARBINARY, LONGVARBINARY byte[] DATE java.sql.Date TIME java.sql.Time TIMESTAMP java.sql.Timestamp