JDBC (2).ppt

JDBC –
Java DataBase Connectivity
CSE432
Object Oriented
Software Engineering

2
What is JDBC?
 “An API that lets you access virtually any tabular data
source from the Java programming language”
 JDBC Data Access API – JDBC Technology Homepage
 What’s an API?
 See J2SE documentation
 What’s a tabular data source?
 “… access virtually any data source, from relational
databases to spreadsheets and flat files.”
 JDBC Documentation
 We’ll focus on accessing Oracle databases

3
General Architecture
 What design pattern is
implied in this
architecture?
 What does it buy for us?
 Why is this architecture
also multi-tiered?

5
Basic steps to use
a database in Java
 1.Establish a connection
 2.Create JDBC Statements
 3.Execute SQL Statements
 4.GET ResultSet
 5.Close connections

6
1. Establish a connection
 import java.sql.*;
 Load the vendor specific driver
 Class.forName("oracle.jdbc.driver.OracleDriver");
 What do you think this statement does, and how?
 Dynamically loads a driver class, for Oracle database
 Make the connection
 Connection con = DriverManager.getConnection(
"jdbc:oracle:thin:@oracle-prod:1521:OPROD", username,
passwd);
 What do you think this statement does?
 Establishes connection to database by obtaining
a Connection object

7
2. Create JDBC statement(s)
 Statement stmt = con.createStatement() ;
 Creates a Statement object for sending SQL statements
to the database

8
Executing SQL Statements
 String createLehigh = "Create table Lehigh " +
"(SSN Integer not null, Name VARCHAR(32), "
+ "Marks Integer)";
stmt.executeUpdate(createLehigh);
//What does this statement do?
 String insertLehigh = "Insert into Lehigh values“
+ "(123456789,abc,100)";
stmt.executeUpdate(insertLehigh);

9
Get ResultSet
String queryLehigh = "select * from Lehigh";
ResultSet rs = Stmt.executeQuery(queryLehigh);
//What does this statement do?
while (rs.next()) {
int ssn = rs.getInt("SSN");
String name = rs.getString("NAME");
int marks = rs.getInt("MARKS");
}

10
Close connection
 stmt.close();
 con.close();

11
Transactions and JDBC
 JDBC allows SQL statements to be grouped together into a
single transaction
 Transaction control is performed by the Connection object,
default mode is auto-commit, I.e., each sql statement is treated
as a transaction
 We can turn off the auto-commit mode with
con.setAutoCommit(false);
 And turn it back on with con.setAutoCommit(true);
 Once auto-commit is off, no SQL statement will be committed
until an explicit is invoked con.commit();
 At this point all changes done by the SQL statements will be
made permanent in the database.

12
Handling Errors with
Exceptions
 Programs should recover and leave the database in
a consistent state.
 If a statement in the try block throws an exception or
warning, it can be caught in one of the
corresponding catch statements
 How might a finally {…} block be helpful here?
 E.g., you could rollback your transaction in a
catch { …} block or close database connection and
free database related resources in finally {…} block

13
Another way to access database
(JDBC-ODBC)
What’s a bit different
about this
architecture?
Why add yet
another layer?

14
Sample program
import java.sql.*;
class Test {
public static void main(String[] args) {
try {
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); //dynamic loading of driver
String filename = "c:/db1.mdb"; //Location of an Access database
String database = "jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)};DBQ=";
database+= filename.trim() + ";DriverID=22;READONLY=true}"; //add on to end
Connection con = DriverManager.getConnection( database ,"","");
Statement s = con.createStatement();
s.execute("create table TEST12345 ( firstcolumn integer )");
s.execute("insert into TEST12345 values(1)");
s.execute("select firstcolumn from TEST12345");

15
Sample program(cont)
ResultSet rs = s.getResultSet();
if (rs != null) // if rs == null, then there is no ResultSet to view
while ( rs.next() ) // this will step through our data row-by-row
{ /* the next line will get the first column in our current row's ResultSet
as a String ( getString( columnNumber) ) and output it to the screen */
System.out.println("Data from column_name: " + rs.getString(1) );
}
s.close(); // close Statement to let the database know we're done with it
con.close(); //close connection
}
catch (Exception err) { System.out.println("ERROR: " + err); }
}
}

17
JDBC 2 – Scrollable Result Set
…
Statement stmt =
con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_READ_ONLY);
String query = “select students from class where type=‘not sleeping’ “;
ResultSet rs = stmt.executeQuery( query );
rs.previous(); / / go back in the RS (not possible in JDBC 1…)
rs.relative(-5); / / go 5 records back
rs.relative(7); / / go 7 records forward
rs.absolute(100); / / go to 100th record
…

18
JDBC 2 – Updateable ResultSet
…
Statement stmt =
con.createStatement(ResultSet.TYPE_FORWARD_ONLY,
ResultSet.CONCUR_UPDATABLE);
String query = " select students, grade from class
where type=‘really listening this presentation’ “;
ResultSet rs = stmt.executeQuery( query );
…
while ( rs.next() )
{
int grade = rs.getInt(“grade”);
rs.updateInt(“grade”, grade+10);
rs.updateRow();
}

19
Metadata from DB
 A Connection's database is able
to provide schema information
describing its tables,
its supported SQL grammar,
its stored procedures
the capabilities of this connection, and so on
 What is a stored procedure?
 Group of SQL statements that form a logical unit
and perform a particular task
This information is made available through
a DatabaseMetaData object.

20
Metadata from DB - example
…
Connection con = …. ;
DatabaseMetaData dbmd = con.getMetaData();
String catalog = null;
String schema = null;
String table = “sys%”;
String[ ] types = null;
ResultSet rs =
dbmd.getTables(catalog , schema , table , types );
…

21
JDBC – Metadata from RS
public static void printRS(ResultSet rs) throws SQLException
{
ResultSetMetaData md = rs.getMetaData();
// get number of columns
int nCols = md.getColumnCount();
// print column names
for(int i=1; i < nCols; ++i)
System.out.print( md.getColumnName( i)+",");
/ / output resultset
while ( rs.next() )
{ for(int i=1; i < nCols; ++i)
System.out.print( rs.getString( i)+",");
System.out.println( rs.getString(nCols) );
}
}

22
JDBC and beyond
 (JNDI) Java Naming and Directory Interface
 API for network-wide sharing of information about users,
machines, networks, services, and applications
 Preserves Java’s object model
 (JDO) Java Data Object
 Models persistence of objects, using RDBMS as repository
 Save, load objects from RDBMS
 (SQLJ) Embedded SQL in Java
 Standardized and optimized by Sybase, Oracle and IBM
 Java extended with directives: # sql
 SQL routines can invoke Java methods
 Maps SQL types to Java classes

24
JDBC references
 http://java.sun.com/products/jdbc/index.html
 JDBC Database Access – The Java Tutorial
 http://java.sun.com/docs/books/tutorial/jdbc/index.html
 http://java.sun.com/j2se/1.4.2/docs/guide/jdbc/index.html
 java.sql package
 http://java.sun.com/j2se/1.4.2/docs/api/java/sql/package-summary.html
 JDBC Technology Guide: Getting Started
 http://java.sun.com/j2se/1.4.2/docs/guide/jdbc/getstart/GettingStartedTOC.fm.html
 JDBC API Tutorial and Reference (book)
 http://java.sun.com/docs/books/jdbc/

25
JDBC
 http://java.sun.com/products/jdbc/index.html
 JDBC Database Access – The Java Tutorial
 http://java.sun.com/docs/books/tutorial/jdbc/index.html
 http://java.sun.com/j2se/1.4.2/docs/guide/jdbc/index.html
 java.sql package
 http://java.sun.com/j2se/1.4.2/docs/api/java/sql/package-summary.html
 JDBC Technology Guide: Getting Started
 http://java.sun.com/j2se/1.4.2/docs/guide/jdbc/getstart/GettingStartedTOC.fm.html
 JDBC API Tutorial and Reference (book)
 http://java.sun.com/docs/books/jdbc/

JDBC (2).ppt

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