1 CSE5200 JDBC and JDeveloper JDBC java.sql package java.sql classes.

1

CSE5200JDBC and JDeveloper

• JDBC• java.sql package• java.sql classes

2

References

• Orfali, Harkey & Evans Client Server Survival Guide (3rd ed) 1999 Ch.11 p.237-249

• www.javasoft.com• Orfali, R. and Harkey, D (1998) Client/Server

Programming with JAVA and CORBA (2nd Ed.) Wiley Ch. 23, 25

3

JDBC

• SQL database access is the most prevalent client/server application model– I.e these are the services we require most

• JDBC– is the Java object version of Microsoft ODBC

– defines Java class wrappers for SQL database access

– can access almost any database service

– JDBC drivers are available from almost any Java vendor

– java.sql.* package is now part of the Java core

4

JDBC

– compliance means the drivers support SQL92– must implement the java.sql.* classes– must be thread safe

• JDBC Naming Convention• jdbc:oracle:oci7:@db", "scott", "tiger”

• subprotocol this could be a URL

• JDBC Classes– JDBC Core Interfaces– Java Language extensions– Java Utility Extensions– SQL Metadata Interfaces

5

JDBC Core

• Classes– locate DBMS drivers - DriverManagerClass

• locates the driver for DB you specify

– establish connections• commit, rollback and the DB isolation level

– submit SQL statements• 2 extensions

– Prepared statement - precompile and execute

– Callable statement - stored procedures

– process result set• manipulate the cursor and get back results

6

Java.sql.*

• Oracle extensions - the Oracle JDBC classes contained in the classes111.zip file - contain a set of classes that invoke the core classes contained in the java.sql.* package

• the java.sql.* package was not part of the core classes in JDK 1.0

7

JDBC Drivers

8

Typical Steps

• Import the JDBC Package • Set useful static class variables for driver, DBMS URI,

credentials, etc. • Register appropriate driver with the DriverManager

class • Set connection Properties (typically credentials) • Invoke the Connection• Create SQL statement in a String • Invoke Statement on connection • Execute SQL statement via appropriate method on

Statement object (PTO)

9

Typical Steps

execute(...), executeQuery(...) for SEL, receive ResultSet/s executeUpdate(...) for INS/DEL/UPD or DDLs, receive

integer value indicating row count automatic commit, unless disabled, in which case an explicit

COMMIT must be executed to save changes to database• Check for Exceptions • Process ResultSet NB: Columns numbered from 1. • Close ResultSet and Statement Unless multiple transactions, then redefine and reuse • Cycle for further operations • Close Connection

10

Registering & Connecting:The DriverManager Class

• oracle.jdbc.driver (classes to support database access and updates in Oracle type formats)

• // Load the Oracle JDBC driver

• DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver()); or

• Class.forName ("oracle.jdbc.driver.OracleDriver");

• // Connect to the database

• Connection conn = DriverManager.getConnection ("jdbc:oracle:thin:@CSE5200A", “S1234567", “student");

11

Sample Code

• Code for creating a connection using JDBC with Oracle• try • { // register the driver to connect to oracle• DriverManager.registerDriver (new oracle.jdbc.driver.OracleDriver());• // db_con is a connection object that lets us connect to the • // database with specified URL/userid/password• Connection db_con = DriverManager.getConnection

("jdbc:oracle:thin:@llama.its.monash.edu.au:1521:CSE5200A", "studentid", "password");

• System.out.println("Connection Success");• }• catch(SQLException f)• { // gives error if the above did not succeed.• System.out.println("Connection Failed. SQL Exception");• }

12

• Code to retrieve data from the Database using the previously created JDBC Connection object• try • { // statement object stmt created to execute queries using db_con • Statement stmt = db_con.createStatement();• // rset is an object that holds the result of the query• ResultSet rset = stmt.executeQuery ("SELECT * FROM authors"); • // looping through the resultset object till end• while (rset.next()){• // getString gets the string data in col 1 of result• // and we would have rset.getInt(2) if col 2 was an integer• System.out.println (rset.getString(1)); • }• • }• catch(SQLException f)• { // error handling for above• System.out.println("Cannot retrieve data SQL Exception occured");• }

13

Transactions:The Connection Interface

• Connection Interface– Session between application and database

– Specified by location (URI) and credentials • Commit/Rollback

– conn.commit();– conn.rollback();

• Ignore Isolation Levels• Set Autocommit off

– after connect but before any statement

• conn.setAutoCommit (false);

14

Creating a Statement Object:Connection Interface

• Statement stmt = conn.createStatement ();• stmt.execute (“select empno from emp”);

– no parameters• PreparedStatement pmst = conn.prepareStatement

(“insert into emp (EMPNO, EMPNAME) values (?, ?)”);- setting and getting parameters next slide

• pstmt.execute();• selectText = "SELECT firstname,lastname FROM addresses";

• Statement selectStmt = dbConnection.createStatement();

• ResultSet result = selectStmt.executeQuery(selectText);

• insertText = "INSERT INTO addresses VALUES (1,'John','Smith')";

• Statement insertStmt = dbConnection.createStatement();

• int rowsInserted = insertStmt.executeUpdate(insertText);

15

Setting Parameters & Getting Fields

• PreparedStatement statement is pre-compiled and stored in a PreparedStatement

object. Can use this to efficiently execute the statement multiple times

allows IN parameters within the query referenced by number setXXX () methods used

• setXXX();– pstmt.setString (1, "SCOTT");

• getXXX();– System.out.println( rset.getString (1) );

• setNULL(); - don’t use nulls

16

ResultSet Interface

• Provides access to a table of data generated by executing a Statement

• Table rows are retrieved in sequence via a cursor pointing to the current row of data

• Some methods: next ()

getXXX () methods

wasNull ()—detect SQL NULL values

close ()

17

Executing a Query and Returning the ResultSetResultSet Interface

• ResultSet rset = stmt.executeQuery ("SELECT ename FROM emp");

• executeUpdate – insert, delete, update

• execute(): • while (rset.next())

System.out.println (rset.getString(1));

• This is standard JDBC syntax. The next() method returns false when it reaches the end of the result set. The employee names are materialized as JavaStrings.

18

Closing the ResultSet, Statement and Connection

• You must explicitly close the ResultSet and Statement objects after you finish using them.

• rset.close();• stmt.close(); • You must close your connection to the database once you finish

your work. • conn.close();

19

ResultSet Interface

void dispResultSet (ResultSet rs) throws SQLException

{ while (rs.next ())

{ System.out.print ("" + rs.getInt (1))

String firstName = rs.getString ("FIRST_NAME");

System.out.print (rs.wasNull () ? “[no first name]” : firstName);

System.out.print (rs.getString ("LAST_NAME"));

System.out.println (rs.getDate (4)); }

rs.close (); }

20

SQLException

• getMessage(): returns the error message associated with the object that threw the exception

• printStackTrace(): prints this object name and its stacktrace to the specified print stream

• This example uses both getMessage() and printStackTrace() to return errors.

• catch(SQLException e); {• System.out.println("exception: " + e.getMessage());

• e.printStackTrace(); } OR

21

SQL Exception continued

• catch (SQLException e) {• while(e != null) {• System.out.println(e.getMessage());• e = e.getNextException();• password = readEntry ("hold it: "); }

22

SQLJ Overview

• Embedding SQL statements into a host language - Java

• Opposed to a CLI to access the database - JDBC

• SQLJ is similar to the ANSI/ISO embedded SQL standards for C, Fortran and other programming languages

– proposed to ANSI/ISO as the SQL and Java Standard

– (ANSI x.3.135.10-1998)

• In Oracle terms Pro*Java

• Created by IBM, Oracle, Sybase and Tandem because

– OO languages have better type checking

– no need for writing a dynamic component because JDBC already exists

23

SQLJ Architecture

*.SQLJ

Oracle

SQLJtranslator *.JAVA

Oracle

Custom

iser

Java Byte Code

JavaCompilerJAVAC

RunOracle

sqlj MyFile.sqlj MyOtherFile.sqlj MyJavaFile.java

24

SQLJ Runtime Configuration

SQLJ Application

SQLJ Runtime Lib

Javasoft ODBC based drivers

Oracle JDBC/OCI

drivers

Oracle thin JDBC driver

ODBC C Library

OCI C Library

Java sockets