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CSE5200JDBC and JDeveloper

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

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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

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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

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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

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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

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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

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JDBC Drivers

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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)

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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

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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");

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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");• }

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• 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");• }

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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);

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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);

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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

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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 ()

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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.

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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();

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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 (); }

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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

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SQL Exception continued

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

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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

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SQLJ Architecture

*.SQLJ

Oracle

SQLJtranslator *.JAVA

Oracle

Custom

iser

Java Byte Code

JavaCompilerJAVAC

RunOracle

sqlj MyFile.sqlj MyOtherFile.sqlj MyJavaFile.java

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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