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ICT337 Advanced Software Development
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Topic 5
Topic 5
JDBC
 Database systems, database languages
 Relational database model
 Structured Query Language (SQL)
 A note on JDBC and ODBC
 A Java programming example
 A note on the ResultSet interface
 JDBC, servlets, RMI, CORBA
 Transaction processing
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Database systems
A database system is an integrated collection of data. A database system involves
 the data itself,
 the hardware on which the data reside,
 the software (called a database management system or DBMS) that controls the
storage and retrieval of data, and
 of course, the users themselves.
Having a database system allows data redundancy and inconsistency to be avoided,
data integrity to be maintained, data standards to be enforced, (most importantly) the
sharing of the data, and security restriction to be enforced.
Database systems organize data in a manner that allows one to pose queries on the
data (i.e. to request information that satisfies given criteria).
A distributed database is a database that is spread across the computer systems of
network. Usually in such systems each data item is stored at the location where it is
most frequently used, but the database is accessible to other network users.
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Database languages
Users access a database via statements in a database language. Application programs
may use a conventional high-level language like Java, C, C++, Visual Basic, or
Pascal.
A user may make requests of the database in a specially designed query language that
makes it easy to express requests in the context of a particular application.
Such languages are referred to as host languages. Each host language ordinarily
includes a database sublanguage (DSL) concerned with the specifics of database
objects and operations.
Each database sublanguage is a combination of two languages:
 a data definition language (DDL) which provides facilities for defining database
objects
 a data manipulation language (DML) which provides features for specifying the
processing to be performed on database objects
The query language that we will use in this topic is the popular Structured Query
Language (SQL).
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SQL provides both DDL and DML.
The most popular style of database system on the kinds of computers that use Java is
the relational database, although in recent years, object-oriented databases have also
become popular.
Java enables programmers to write code that uses SQL queries to access the
information in relational database systems. Some popular relational database
software packages include Microsoft Access, Sybase, Oracle, Informix, Microsoft
SQL server.
In this topic, we will use the Java Database Connectivity (JDBC) to manipulate a
Microsoft Access database.
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Relational Database Model
The relational database model developed by Codd is a logical representation of the
data that allows the relationships between the data to be considered without
concerning oneself with the physical implementation of the data structures.
A relational database is composed of tables (rows and columns). A sample table is
given below:
Table:
EMPLOYEE
A
record
Number
Name
Department
Salary
Location
23606
Jones, A
413
2100
Perth
24533
Kerwin, R
413
1500
Perth
27799
Larson, P
642
1800
Melbourne
34433
Myers, B
611
2000
Sydney
34590
Neumann, C
610
1200
Brisbane
Primary
key
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A column
(or field)
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The primary key is unique and is used for data referencing. Primary keys are
normally used in tables but not compulsory. If used, primary key fields cannot
contain duplicate values. The primary key can be composed of more than one column
(or field).
Certain subsets of a table can be created by the so-called projection operation.
Several smaller tables can also be combined into a larger, more complex table. The
combination operation is called a join operation.
Eg. we can use the projection operation to create a new table called DEPARTMENTLOCATOR whose purpose is to show where departments are located:
Table: DEPARTMENT-LOCAOR
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Department
Location
413
Perth
642
Melbourne
611
Sydney
610
Brisbane
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Structured Query Language
SQL queries are composed of SQL keywords and table name(s) and possibly field
(column) names. Below is a table of SQL keywords:
SQL keyword
Description
SELECT
Select (retrieve) fields from one or
more tables
FROM
Tables from which to get fields.
Required in every SELECT
WHERE
Criteria for selection that determine
the rows to be retrieved
GROUP BY
How to group records
HAVING
Used with the GROUP BY clause to
specify criteria for grouping records
in query results
ORDER BY
Criteria for ordering of records
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INNER JOIN
Used for merging multiple tables into
a larger, more complex one
INSERT INTO
Used for inserting a record into a
table
UPDATE
Used for updating an existing record
SET
Used in conjunction with UPDATE
Although SQL queries are case insensitive, SQL keywords are normally written in
uppercase while column names are normally in mixed cases for legibility.
Consider a database consisting of 4 tables whose names are Authors, Publishers,
AuthorISBN and Titles respectively, as shown on the following page:
(primary keys are shown in bold)
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We will use these tables for our SQL query examples.
Titles
Publishers
PublisherID
PublisherName
1
ISBN
Title
EditionNumber
1 
AuthorISBN
ISBN
AuthorID

YearPublished
Description
 PublisherID
Authors
1 AuthorID
FirstName
LastName
YearBorn
The PublisherID field in the Titles table is referred to as the foreign key – a field in
a table for which every entry has a unique value in another table and where the field in
the other table is the primary key for that table (ie. PublisherID in the Publishers
table).
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Likewise, the AuthorID field of the AuthorISBN table is a foreign key of the AuthorID
field of the Authors table.
Foreign keys are specified when creating the table.
The foreign keys help maintain the rule of referential integrity. They enable
information from multiple tables to be joined for analysis purpose.
There is a one-to-many relationship between a primary key and its corresponding
foreign key.
 Basic SELECT query
has one of the following forms:
SELECT * FROM TableName
SELECT field1, …, fieldn FROM TableName
Eg.
SELECT * FROM Authors
SELECT AuthorID, LastName FROM Authors
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 WHERE clause
has the following form:
SELECT * FROM TableName WHERE criteria
The WHERE clause condition can contain operators <, >, <=, >=, =, <>, and LIKE.
The LIKE operator is used for pattern matching with wildcard characters asterisk
(*) and question mark (?).
Eg.
SELECT * FROM Authors WHERE YearBorn > ’1960’
SELECT * FROM Authors WHERE LastName LIKE ’D*’
SELECT * FROM Authors WHERE LastName
LIKE ’?[a-I]*’
NOTE: Not all database systems support the LIKE operator.
Criteria in a WHERE clause can be compound, ie. containing AND and/or OR keywords
that join up simple criteria.
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Eg.
SELECT * FROM Titles WHERE
YearPublished > ’1992’ AND
YearPublished < ’1999’
SELECT * FROM Titles WHERE
EditionNumber = ’2’ OR
EditionNumber = ’3’
Quotes required here
because
EditionNumber and
YearPublished are
both of Text type (see
Appendix C)
 Grouping records using the GROUP BY clause
The GROUP BY clause has a similar effect as the ORDER BY clause except all the fields
(or columns) must be specified and the wildcard character ‘*’ cannot be used. The
simplest format of this clause is:
SELECT field_1,…,field_n FROM Table
GROUP BY Field_2, Fieldn, …,Field1
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Here, field_i's and Field_i's are the same fields but in different orders and there is a
one-to-one correspondence between them. Eg.
SELECT LastName, FirstName, YearBorn
FROM Authors GROUP BY
YearBorn, Lastname, FirstName
NOTE: SELECT
character ‘*’.
* FROM Table GROUP BY …
is not allowed since it uses the wildcard
NOTE: the GROUP BY clause can be replaced with the ORDER BY clause (see later)
and is therefore seldom used. For instance, the above SELECT statement can be
replaced with
SELECT LastName, FirstName, YearBorn
FROM Authors ORDER BY
YearBorn, Lastname, FirstName
 The Having clause
This clause must be used with the GROUP
is:
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BY
clause. The simplest form of the clause
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SELECT field1, ..., fieldn FROM TableName
GROUP BY Field1, ..., Fieldn
HAVING criteria
where the “GROUP BY…” phrase must appear before the “HAVING…” phrase. The
HAVING clause can be replaced with the WHERE clause. The latter is more commonly
used in SQL queries. For examples, the following two SQL queries produce the
same output:
SELECT LastName, FirstName, YearBorn
GROUP BY LastName, FirstName, YearBorn
HAVING YearBorn > 1930
SELECT LastName, FirstName, YearBorn
WHERE YearBorn > 1930
ORDER BY LastName, FirstName, YearBorn
Note that, unlike the first example, the WHERE clause for the criteria must appear
before the ORDER BY clause in the second example.
 The ORDER BY clause
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The result of a query can be arranged in ascending or descending order using the
optional ORDER BY clause. The simplest form of this clause is:
SELECT * FROM TableName ORDER BY field ASC
SELECT * FROM TableName ORDER BY field DESC
where ASC specifies ascending order, DESC specifies descending order.
Eg.
SELECT * FROM Authors ORDER BY LastName ASC
NOTE: Multiple fields can be used for ordering purpose:
ORDER BY field1 SortingOrder, field2 SortingOrder
where SortingOrder is either ASC or DESC. SortingOrder does not have to be
identical for each field. If SortingOrder is not given then ASC is assumed. Eg.
SELECT * FROM Authors ORDER BY LastName,
FirstName
SELECT LastName, FirstName, YearBorn FROM
Authors ORDER BY YearBorn
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The WHERE and ORDER
BY
Topic 5
clauses can be combined in one query.
 Using INNER JOIN to merge data from multiple tables
An INNER JOIN clause merges records from two or more tables by testing for
matching values in a field that is common to both tables. The simplest form of an
INNER JOIN clause is
SELECT * FROM Table1 INNER JOIN Table2 ON
Table1.field = Table2.field
Eg.
SELECT FirstName, LastName, ISBN FROM
Authors INNER JOIN AuthorISBN
ON Authors.AuthorID = AuthorISBN.AuthorID
ORDER BY LastName, FirstName
The keyword INNER JOIN is seldom used since the queries with the INNER JOIN
keywords can be replaced with those without, eg. the above query can be replaced
with
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SELECT FirstName, LastName, ISBN FROM
Authors, AuthorISBN
WHERE Authors.AuthorID = AuthorISBN.AuthorID
ORDER BY LastName, FirstName
to obtain the same result.
Here, the ON keyword that must be used in conjunction with the INNER
keyword is replaced with the WHERE keyword.
JOIN
When joining multiple tables, errors or null results may occur if certain columns
have missing information. Consider the following tables in a Company database
(file Company.mdb)
Table: Employee
EmployeeID
7521
7782
7839
7844
7900
7934
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LastName
Ward
Clark
King
Turner
James
Miller
DeptNumber
30
10
10
30
30
10
Table: Department
DeptNumber
10
30
40
DeptName
Accounting
Sales
Operations
Location
New York
Chicago
Boston
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The SQL query
SELECT Department.DeptName, Employee.Lastname
FROM Department, Employee where
Department.DeptNumber = Employee.DeptNumber
works despite DeptNumber 40 being not found in the Employee table.
However, some database systems which support the outer join operation would
automatically fill in default value (e.g. null or NA) for missing information.
 Using INSERT INTO to insert a record
An INSERT
is
INTO
clause inserts a record into a table. The basic format of the clause
INSERT INTO TableName (ColumnName1,
ColumnName2, ...) VALUES (’value1’,
’value2’, ...)
Eg.
INSERT INTO Authors (AuthorID, FirtName,
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LastName, YearBorn) VALUES
(’4’, ’Joe’, ’Wigglesworth’, ’1955’)
that not all the fields must be given in an INSERT INTO
Note
statement. It is a good
practice to leave out the primary key and let it be generated automatically.
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
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Using UPDATE to update an existing record
A basic UPDATE SQL statement has the form
UPDATE TableName SET ColumnName1=’value1’,
ColumnName2=’value2’, ...
WHERE criteria
Note that not all the columns have to be included in the UPDATE statement.
Note also the use of single quotes in the
Statement.
No quotes around number 3 since
AuthorID is of type integer
Criteria
involves
reference to the
primary key
Eg.
UPDATE Authors SET FirstName=’John’,
LastName=’Donn’ WHERE AuthorID=3
UPDATE Authors SET FirstName=’John’
WHERE LastName=’Donn’
The second example above updates the first
name of all the records that have the last name
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Criteria
involves
reference
to an
ordinary
field
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equal to “Donn”
JDBC
 API for database access.
 Allows a developer to access a database at any location to query, insert, update,
etc.
 Similar API’s exist in most popular programming languages.
 Three main goals when developing
o JDBC should be a SQL-level API.
o JDBC should capitalize on the experience of existing database APIs.
o JDBC should be simple.
 An SQL-level API means that JDBC allows you to construct SQL statements and
embed them inside Java API calls.
 In short, you are basically using SQL. But JDBC lets you smoothly translate
between the world of the database and the world of the Java application.
 Your results from the database, for instance, are returned as Java objects, and
access problems get thrown as exceptions.
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 JDBC is probably more difficult than other API’s because of the use of classes
and exceptions. However, to a developer who has reasonable java skills, JDBC is
still an easy to use API for working with databases.
A note on JDBC and ODBC
1. ODBC (Open Database Connectivity) is a Microsoft standard API that provides
access to a multitude of existing databases.
2. JDBC is a pure Java API
3. ODBC is a C or C++ API, using lots of pointers, it is mostly Microsoft Windowsplatform specific.
4. JDBC works on any platform running the Java Virtual Machine (JVM).
5. JDBC is also an object-oriented API and so is easier to learn and implement than
the ODBC API.
6. JDBC provides the ability to pass new SQL statements directly to the data source.
7. JDBC architecture supports the functionality of common database bridges such as
ODBC.
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You can access nearly any database through the JDBC API including Microsoft
Access, Informix, Oracle, Sybase, xBase.
JDBC provides this broad database support through 4 types of connectivity (via
drivers). The JDBC-ODBC bridge belongs to the first type of driver:
Type 1: JDBC-ODBC bridge
o JDBC-ODBC bridge driver provided by Sun with the Java SDK is an example of
a type 1 driver
o JDBC-ODBC allows existing ODBC drivers to be used through the JDBC API
o Not the best solution – requires ODBC driver to be installed
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o A type 1 driver merely translates queries obtained by the driver into equivalent
ODBC queries and forwards directly to the ODBC driver via native API calls.
client
JDBC driver
ODBC driver
database
native
The JDBC-ODBC bridge provided by the Java Development Kit (jdk) allows one to
manipulate a database (in this case, a Microsoft Access database) via JDBC so long as
the database has been registered as an ODBC Data Source. Appendix A shows the
steps for the registration.
The registration above requires that the ODBC driver has been installed on the
machine. Several products (eg. most Microsoft Office) provide the option to install
the ODBC driver.
Visit the web site http://java.sun.com/products/jdbc for the latest info from Sun
regarding JDBC drivers.
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The other 3 types of JDBC drivers are:
2) Native-API, partly Java eg java program uses Java Native Interface to call a
database specific API written in C++ to access a database directly
3) JDBC-Net pure Java driver: takes JDBC requests, turns them into a networkprotocol and sends to a server which interacts with a database
4) Native-protocol pure Java driver: database-specific network protocol allowing
direct connection to a database.
Using JDBC (Basic Steps)
 The examples used in these notes are available on the ftp site. You will need to
setup up an access ODBC Driver with the name Publications to run the
programs.
1. Specify the location of the database. This will generally involve specifying the
ODBC or type 4 driver.
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a. ODBC
String url = ”jdbc:odbc:Publications”;
here we specify that jdbc is the protocol, we are using odbc as the
subprotocol, and Publications is the name of the odbc that must exist on
the system we are running the application from.
b. Type 4
String url = ”jdbc:mysql://localhost/ict337
here we specify that jdbc is the protocol, we are connecting to a mysql
database server and requesting a connection to the ict337 database.
2. Specify the driver to use for the connection.
a. ODBC
String dbDriver="sun.jdbc.odbc.JdbcOdbcDriver”;
here we specify that jdbc odbc bridge driver that is built-in to JDBC.
b. Type 4
String dbDriver="com.mysql.jdbc.Driver";
here we specify a type 4 driver for MySql. This driver will need to be
present in the classpath of the machine, but nothing special needs to be
done to make it ready for use. Normally you would just package this up
with your application.
3. Create an instance of the class of the JDBC driver.
Class.forName(dbDriver);
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4. Create a connection to the database with the DriverManager class
Connection con = DriverManager.getConnection(url, username, password);
Once a Driver recognizes your URL, it creates a database connection using the properties you
specified. It then provides the DriverManager with a java.sql.Connection implementation
representing that database connection. The DriverManager then passes that Connection object
back to the application.
5. Do something with/to database.
6. Close the connection
con.close();
Simple example (ex1Connection.java)
import java.sql.*;
public class ex1Connection
{
static public void main(String args[])
{
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//String url = "jdbc:mysql://localhost/ict337";
//String dbDriver="com.mysql.jdbc.Driver";
//access
String url="jdbc:odbc:Publications";
String dbDriver="sun.jdbc.odbc.JdbcOdbcDriver";
String username="your";
String password="mother";
Connection connection = null;
try
{ // load the driver
Class.forName(dbDriver);
}
catch( Exception e )
{ // problem loading driver, class not exist?
e.printStackTrace( );
return;
}
try
{
connection = DriverManager.getConnection(url,username,password);
System.out.println("Connection successful!");
// Do whatever queries or updates you want here!!!
}
catch( SQLException e )
{
e.printStackTrace( );
}
finally
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{
if( connection != null )
{
try
{
connection.close( );
System.out.println("connection closed successfully");
}
catch( SQLException e )
{
e.printStackTrace( );
}
}
}
}
}
Database Access
The fundamental classes for database access are Statement, Prepared Statement, and
ResultSet.
Statement Class
 The Statement class is the most basic of three JDBC classes representing SQL
statements.
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 It performs all of the basic SQL statements. In general, a simple database
transaction uses only one of the three statement execution methods in the
Statement class.
 The first such method, executeQuery(), takes a SQL String as an argument and
returns a ResultSet object. This method should be used for any SQL calls that
expect to return data from the database (select).
 Update statements, on the other hand, are executed using the executeUpdate( )
method. This method returns the number of affected rows. Use this for update,
insert, delete, etc.
 Statement also provides an execute() method for when you don’t know whether
the query is a select query or an update.
Simple Query Method (ex2SelectQuery.java for full program)
public static void query(Connection con, String sql)
{
try
{
//create the sql statement object
Statement s = con.createStatement();
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//execute the sql and get the result
ResultSet res=s.executeQuery(sql);
if(res==null)
{
System.out.println("no results");
return;
}
//loop through the results and display each row
while(res.next())
{
//print out the publisherID
System.out.print(res.getInt("PublisherID")+" ");
//print out the publisher name
System.out.println(res.getString("PublisherName"));
}
}
catch(SQLException e)
{
System.out.println("Exception");
return;
}
}
Only 2 statements are required to execute the queryStatement s = con.createStatement();
ResultSet res=s.executeQuery(sql);
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 The first statement creates a statement object. The second executes the
statement with the supplied parameter sql. The parameter sql, should of
course contain a string with a valid sql statement starting with ‘select’.
 It returns a ResultSet object, which is an object containing the result of the
sql query. The ResultSet will be null if no results are returned.
 You need to use the next() method of the ResultSet object to move to the
next row of the results. The next() method will return false when there are no
more rows in the result. It will throw SQLException if the ResultSet is null,
so make sure ResultSet is not null before calling next().
 To retrieve a field from the ResultSet, use one of the get methods, i.e.
getString(), getInt(), etc to retrieve a field. You need to specify the type of
the field to retrieve it. In the example above, the statement
res.getInt("PublisherID") retrieves the field PublisherID from the current row in
the ResultSet as an integer.
Simple Update Method (ex3UpdateQuery.java for full program)
public static int updateQuery(String sql,Connection con)
{
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try
{
Statement s=con.createStatement();
return s.executeUpdate(sql);
}
catch(SQLException e)
{
return 0;
}
}
 As you can see, updates are very simple and require less developer processing
as we generally only want to know how many rows were affected.
 Here use the executeUpdate() method which returns an integer containing the
number of rows affected (inserts, deletes, etc.
Creating / deleting tables (ex4CreateDeleteTables.java for program)
A new table can be created in the database with your Java code, using the
executeUpdate() method. e.g
Statement s = connect.createStatement();
s.executeUpdate(”CREATE TABLE temp” +
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”(ID int, name varchar(25), marks float)”);
// now insert two records into the table
int insCount = s.executeUpdate(”INSERT INTO Temp”
+ ”VALUES (1234, ’Andrew Clark’, 98.5)”);
System.out.println(”Inserted ” + insCount + ”record”);
int insCount = s.executeUpdate(”INSERT INTO Temp”
+ ”VALUES (1258, ’Tom Brooks’, 51.2)”);
System.out.println(”Inserted ” + insCount + ”record”);
…
To delete a table (say table Temp):
s.executeUpdate(”DROP TABLE Temp”);
s.close();
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The ResultSet interface
Recall that a ResultSet object is returned when a query is executed via a handle of
type Statement:
Connection connection;
String query = ”SELECT * FROM Authors”;
…
Statement statement =
connection.createStatement();
ResultSet rs = statement.executeQuery(query);
Information about the number of columns, column headings and values of the records
can be obtained by creating a ResultSetMetaData (also an interface) object:
ResultSetMetaData rsmd = rs.getMetaData();
In older JDBC there was no mechanism defined for a result set to scroll backwards –
to avoid the issue of repeatability of data read by a result set.
In JDBC 2, three types of result sets are defined:
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 forward-only – (the constant ResultSet.TYPE_FORWARD_ONLY) this is the same as
JDBC
 scroll-insensitive – (the constant ResultSet.TYPE_SCROLL_INSENSITIVE) Result sets of
this type are scrollable but are not sensitive to changes made by others.
 scroll-sensitive – (the constant ResultSet.TYPE_SCROLL_SENSITIVE) similar to
scroll-insensitive but are sensitive to changes made by others.
Scroll Backwards example (ex5Scrolling.java for full program)
public static void ScrollBack(ResultSet R)
{
if(R!=null)
{
try
{
R.afterLast();
while(R.previous())
{
System.out.print(R.getInt("publisherID")+" ");
System.out.println(R.getString("PublisherName"));
}
}catch(SQLException e)
{
System.out.println("scroll error");
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}
}
}
The ResultSetMetaData interface
Retrieving the value of a column from a ResultSet object requires us to know the type
of that column and either the column heading (e.g. rs.getString(”FirstName”)) or
the column index (e.g. rs.getString(2)). Thus, we must combine the use of methods
in the ResultSetMetaData interface, e.g.
String getColumnName(int column)
int getColumnType(int column)
String getTableName(int column)
int getColumnCount()
boolean isReadOnly(int column)
Some example methods
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The first method returns an array of strings containing the column names
public static String[] getColumnNames(ResultSetMetaData rsmd)
{
if(rsmd==null)
return null;
String colNames[] = new String[getColumnCount(rsmd)];
try
{
for(int counter=0;counter<colNames.length;counter++)
colNames[counter]=rsmd.getColumnName(counter+1);
}
catch(SQLException e)
{
return null;
}
return colNames;
}
The second method returns an integer representing the number of rows in the
resultset.
public static int getColumnCount(ResultSetMetaData rsmd)
{
if(rsmd==null)
return 0;
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try
{
return rsmd.getColumnCount();
}
catch(SQLException e)
{
return 0;
}
}

Combining the two metadata methods above we can make more dynamic applications that
do not require a knowledge of the number of data type of columns returned.

Example printing out results without knowledge of column names. (ex6MetaData.java)
import java.sql.*;
public class metadata {
public static int getColumnCount(ResultSetMetaData rsmd)
{
if(rsmd==null)
return 0;
try
{
return rsmd.getColumnCount();
}
catch(SQLException e)
{
return 0;
}
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}
public static String[] getColumnNames(ResultSetMetaData rsmd)
{
if(rsmd==null)
return null;
String colNames[] = new String[getColumnCount(rsmd)];
try
{
for(int counter=0;counter<colNames.length;counter++)
colNames[counter]=rsmd.getColumnName(counter+1);
}
catch(SQLException e)
{
return null;
}
return colNames;
}
public static void printResults(ResultSet R)
{
if(R==null)
{
System.out.println("No results");
}
else
{
try{
ResultSetMetaData rsmd=R.getMetaData();
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String[] colNames=getColumnNames(rsmd);
for(int i=0;i< colNames.length;i++)
{
System.out.print(colNames[i]+"\t");
}
while(R.next())
{
System.out.println();
for(int i=0;i< colNames.length;i++)
{
System.out.print(R.getString(colNames[i])+"\t");
}
}
}catch(SQLException e)
{
System.out.println("exception");
}
}
}
public static ResultSet query(Connection con, String sql)
{
try
{
//create the sql statement object
Statement s = con.createStatement();
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//execute the sql and get the result
ResultSet res=s.executeQuery(sql);
if(res==null)
{
System.out.println("no results");
return null;
}
return res;
}
catch(SQLException e)
{
System.out.println("Exception");
return null;
}
}
static public void main(String args[]) {
String url = "jdbc:mysql://localhost/ict337";
String dbDriver="com.mysql.jdbc.Driver";
String username="your";
String password="mother";
Connection connection = null;
try { // load the driver
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Class.forName(dbDriver);
}
catch( Exception e ) { // problem loading driver, class not exist?
e.printStackTrace( );
return;
}
try {
connection = DriverManager.getConnection(url,username,password);
System.out.println("Connection successful!");
printResults(query(connection,"select * from publishers"));
}
catch( SQLException e ) {
e.printStackTrace( );
}
finally {
if( connection != null ) {
try {
connection.close( );
System.out.println("\nconnection closed successfully");
}
catch( SQLException e ) {
e.printStackTrace( );
}
}
}
}
}
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Batch processing
 Complex systems often require both online and batch processing.
 Each kind of processing has very different requirements.
 Because online processing involves a user waiting on application processing
order, the timing and performance of each statement execution in a process is
important.
 Batch processing, on the other hand, occurs when a bunch of distinct transactions
need to occur independently of user interaction. A bank's ATM machine is an
example of a system of online processes.
 The monthly process that calculates and adds interest to your savings account is
an example of a batch process.
 Batch processing is more efficient than sending single transactions to a database
system. It also makes your code more readable.
 We use the addBatch() and executeBatch() methods to perform batch processing.
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Example Method for batch insert (ex7Batch.java for full program)
public static void doBatch(Connection conn)
{
try
{
Statement stmt = conn.createStatement( );
for(int i=1000; i<1010; i++)
{
String s="insert into publishers values ("+i+", 'you"+i+"')";
System.out.println(s);
stmt.addBatch(s);
}
stmt.executeBatch( );
}
catch(SQLException e)
{
System.out.println("Exception");
return;
}
}
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Transaction processing
A database transaction is a discrete set of database operations with a well-defined begin
point and a well-defined end point, such that the entire set of operations can be treated
as a unit for controlling change to the database.
If the database supports transaction processing, changes made to the database can be
undone. Java provides transaction processing via methods of the interface Connection:
 The method setAutoCommit(boolean autoCommit) specifies if each individual
SQL statement should be performed. Set flag to false if several SQL statements
should be grouped as a transaction.
 If autoCommit==false (ie. do not auto commit) then the method void commit()
must be explicitly called to commit the changes to the database. Otherwise, the
method void rollback() should be called to return the database to its state before
the transaction began.
 The method boolean getAutoCommit() returns the setting of the auto commit flag.
Example:
// open connection…
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A Connection
object
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connection.setAutoCommit(false);
try {
// transaction begins
statement s = connection.createStatement();
s.addBatch(”INSERT...”);
s.addBatch(”UPDATE...”);
s.executeBatch();
connection.commit();
// transaction ends
} catch (SQLException e1) {
try {
// ignore changes
connection.rollback();
} catch (Exception e2) {}
} finally {
// close connection
connection.close();
}
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When the database is on a server with multiple concurrent clients, operations on the
java.sql objects would be multithreaded. If database updates are involved, then a
locking mechanism must be enforced.
The server may adopt one of the following:
 allows multiple clients to update the database but actually does all the transactions
in batch outside user peak hours. Any update violations would have to be dealt
with separately for individual clients.
 keeps a log of which records, over a specified period of time, have been updated
and allows no more than one update to any record over that period. Time stamps
(see the class Timestamp) can be inserted to monitor records’ modification.
See example in the eg2 folder
See example in the eg3 folder
(optional) See the case study example in Section 8.7 of textbook
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Connection pooling
 In real applications (web database, enterprise app) the demands on the database is
normally very heavy.
 The application will generally being making numerous requests of the database
requests per minute (or even per second). Consider something like google.
 Most of the overhead associated with database connections comprises opening
and closing the connection. With many concurrent requests this can lead to a huge
bottleneck.
 If is not feasible (especially in a web environment) to allow clients to maintain an
open connection to the database as this will quickly use up system resources.
 The JDBC Optional Package provides a standardized solution to the problem—
connection pooling.
 Connection pooling is a mechanism through which open database connections are
held in a cache for use and reuse by different parts of an application.
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 The practical aspect of connection pooling is not covered in this unit, however, it
is an important topic for high use databases.
Exception handing / SQL warning

SQLException
– subclass of Exception
Useful methods: getErrorCode(), getSQLState(), etc

SQLWarning
– subclass of SQLException
Used for non-critical errors; useful methods: getWarnings(), clearWarnings()

DataTruncation
– subclass of SQLWarning
A data truncation occurs when you perform a query and do not or cannot process
all of the results
JDBC, servlets, RMI, CORBA
Any Java program can manipulate a personal database that resides on the local file
system. If the Java program is an Applet then it would not be permitted to even
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connect to the database, as reflected from the error message when such an attempt was
made:
java.security.AccessControlException: access denied
(java.lang.RuntimePermission accessClassInPackage.sun.jdbc.odbc)
Unless the Applet is a trusted one (then even update would be granted) – see
practical exercise week5.doc.
 Mounting a network file directory (as a local drive) via NFS so that a database can
be accessed as a local one? Not recommended except for one of the following:
o The database is small and is mainly for a client’s personal use (ie. not shared by
other users), in which case, the client may want the database to be local to his
site.
o The mounting is done by the server. For security reasons, clients should not be
able to bypass the server to directly mount to the database via NFS (unless the
clients have superuser privileges).
 Most companies install their databases on servers or mainframe computers. Security
and reliability of the database is of utmost importance. For Java applications that
run on a distributed system (involving server and client processes), the RDBM is
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always on the server side and often resides on the tier of a multitier architecture that
is furthest away from the end users.
Using servlets (topic 7) and JDBC is just one of many possible ways to access
databases from Java programs. Another way is of course via RMI or CORBA.
However, a ResultSet object that is created on the server after executing a query from
the client side cannot be directly returned to the client because the ResultSet class is
an interface and cannot be marshalled. For servlets, the output from the server would
be in HTML format so marshalling of return data is not required. In any case, due to
security reasons, important but unencrypted data should not be transmitted.
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Appendix A: Registering a Microsoft Access database as an ODBC Data Source
 Select StartSettings  Control Panel  ODBC Data Sources… or under Administrative
Tools depends on OpSys
 In the popped up ODBC Data Source Administrator window, select the User DSN (User
Data Sources) tab, click the Add button.
 In the Create New Data Source window, select Microsoft Access Drive (*.mdb), click the
Finish button.
 In the popped up ODBC Microsoft Access Setup window, choose a meaningful Data
Source Name (relevant to the database and/or project concerned). Key in a short
description for the data source name in the field Description. Click the Select button to
choose the Microsoft Access file (extension is .mdb) that contains the database. If the
database is set up for authorised users only (with a login name and password) then
click the Advanced button. Enter the login name and password (this will be shared by
all authorised users). Click OK.
 When finished, you should see under the User Data Sources list the data source name
that you have just created. Click the OK button to close the ODBC Data Sources
window.
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 The chosen Data Source name is the logical name that the Java program should refer
to in the url string (see the Java examples). Note that the database file does not need
to reside in the same directory as the Java program.
Appendix B: SQL types and Java types
SQL type
Java type
CHAR
String
VARCHAR
String
LONGVARCHAR
String
NUMERIC
java.math.BigDecimal
DECIMAL
java.math.BigDecimal
BIT
boolean
TINYINT
byte
SMALLINT
short
INTEGER
int
BIGINT
long
REAL
float
DOUBLE
double
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BINARY
byte[]
VARBINARY
byte[]
LONGVARBINARY
byte[]
DATE
java.sql.Date
TIME
java.sql.Time
TIMESTAMP
java.sql.Timestamp
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Appendix C: Common types of columns (fields) in Microsoft Access databases
Microsoft
Access
field type
Text
Memo
Number
Currency
AutoNumber
Yes/no
Description
Up to 255 characters
Up to 65535 characters
Integers of 1, 2, 4, 8, or 16 bytes
8 bytes numeric decimal
4-byte automatically generated integers
1 bit to denote On/Off, True/False
When creating a Microsoft Access table, if the data type of a field matches that shown
in column 1 of the table below, then the matching Java type is given in column 2 of
the table (see the class Types). To retrieve the content of that column of a particular
record, use the method given on the column 3 of the table.
Microsoft
Access
field type
Text
Java type
(see class
Types)
Types.VARCHAR
Field value
retrieval
Memo
Types.LONGVARCHAR
rs.getString(i);
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Number
Types.INTEGER
rs.getLong(i);
Currency
Types.NUMERIC
rs.getDouble(i);
AutoNumber
Types.INTEGER
rs.getInt(i);
Yes/No
Types.BIT
rs.getBoolean(i);
where i is the column number, rs is a ResultSet object.
Further reading:
 “Advanced Java 2 – How to Program” Deitel, Deitel, and Santry, Prentice Hall
2002, Chapter 8. (Optional) Study the case study example in Section 8.7, pages
479-514.
 (optional) JDBC Basic Tutorial page on the web:
http://java.sun.com/docs/books/tutorial/jdbc/basics/index.html
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Objectives
At the end of this topic, you should be able to
 describe the relational database model.
 pose SQL queries to select records from a database, insert new records into a database, update existing
records in a database
 describe the JDBC-ODBC bridge driver
 register a Microsoft Access database file as an ODBC data source
 use the classes and interfaces of java.sql package to query a database, insert data into a database and
update data in a database.
 write transaction processing in Java using the appropriate methods provided by the java.sql package.
 understand the importance of data locking when simultaneous updates to the same database are attempted
by many users.
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