Database programming in Java

An introduction to Java Database Connectivity (JDBC)

Introduction

Two standard ways to work with databases in Java JDBC

A Call level interface similar to ODBC SQLJ

SQL code imbedded in Java, like SQL embedded in C

JDBC is the most common way and it’s supported by almost all database vendors

Java Database Connectivity

JDBC is a specification from Sun and part of Java 2

We will talk about JDBC 2 JDBC applications are portable

Switch database without rewriting your program If there is a driver for the database If you use only standard SQL (i.e. no vendor specific

code)

JDBC is the Java version of ODBC There are four levels for JDBC drivers

Level 1 Drivers

Level 1 is a JDBC-ODBC bridge The actual database communication is done

via a ODBC driver Requires the Database client library to be

installed The ODBC drivers and all libraries that the driver

needs Suns JDBC-ODBC bridge is single threaded

Level 2 Drivers

This is a partly Java solution All JDBC calls are converted from to calls in

the vendor specific client API The library must be installed on the client machine

Level 3 Drivers

Level 3 is a multi tier solution On the client it’s all Java

No vendor specific client library is needed The connection is made to a server that

connects to the database The server can use ODBC or some other

technology Several databases can be supported by the

server

Level 4 Drivers

Level 4 is an all Java solution No client API is needed besides the JDBC

Driver This is the most common type, and the one

that we will use All JDBC calls are directly transformed to the

vendor specific protocoll Direct calls from the client to the database

server

Important JDBC Classes/Interfaces java.sql.DriverManager java.sql.Driver java.sql.Connection java.sql.Statement java.sql.PreparedStatement java.sql.CallableStatement java.sql.ResultSet

Scrollable or not Updateable or not

javax.sql.DataSource

java.sql.DriverManager

The DriverManager is responsible for loading the correct Driver

The DriverManager is used to get a connection to the database

java.sql.Driver

This is the actual implementation of the JDBC Driver

The only part that’s vendor specific Used if DriverManager is used to get

connection Loaded with Class.forName(“driverclass”)

The driver name for Mimer SQL is “com.mimer.jdbc.Driver”

java.sql.Connection

A Connection represent an actual connection to the database

The Connection is used to create statements (queries)

A Connection is returned from the DriverManager DriverManger.getConnection(url, username,

password) DriverManager.getConnection(url)

java.sql.Connection – important methods setAutoCommit(boolean) createStatement() prepareStatement(“SQL query”) commit() rollback() close()

ALLWAYS close your connections

java.sql.Connection – important methods getMetaData() returns a DatabaseMetaData

object From the DatabaseMetaData you can get

information about the database Vendor name Version Supported functions

java.sql.Statement

A Statement is the simplest of the statement types

It’s used to pass a query to the database and to return a ResultSet

java.sql.Statement - important methods executeQuery(“sql query”)

Returns a ResultSet execute(“sql query”)

Mostly used when the type of query is unknown executeUpdate(“sql query”) getResultSet() close()

ALLWAYS close your Statements

java.sql.PreparedStatement

A prepared statement is a Statement with parameters

The prefered way if you have conditions in your query

Will be compiled once at the server and then cached

Give you an easier to read code

java.sql.PreparedStatement – important methods Can do all that a Statement can setXXX() is used to set the different

parameters

pstmt = con.prepareStatement(“select * from person where cars=`?”);

pstmt.setInt(1,carId);

pstmt.executeQuery();

java.sql.CallableStatement

CallableStatement is used to prepare and call stored procedures in the database

prepareCall(“statement”) execute()

java.sql.ResultSet

The ResultSet is used to get the information from the Database

Retured from executeQuery() or getResultSet()

Like a cursor in embedded SQL Just like with Connections and Statements,

ALLWAYS close when you’re done

java.sql.ResultSet

Before the first fetch, the position is before the first row

ResultSet can be of several types Updateable

Can be used to perform updates in the database directly Rows can be inserted

Scrollable The cursor can be moved forward and backwards

java.sql.ResultSet – important methods next()

Used when looping over the result Returns true if there was a row to fetch and false otherwise Moves the cursor one step forward The classic loop is while(rs.next()) where rs is a ResultSet

getXXX(position) Gets the column with postion

getXXX(name) Gets the column with the matching name The name is the same as in the select list

java.sql.ResultSet – important methods getMetaData() returns a ResultSetMeta

where you can get information about the ResultSet Number of columns Type of ResultSet NOT the number of rows

javax.sql.DataSource

DataSource can be used instead of DriverManager and Driver If possible, use it

Retrieved via JNDI (Java Naming and Directory Interface)

DataSource ds = (DataSource)context.lookup(“java:com/env/jdbc/multi1”);

ds.getConnection();

Simple example

1. package com.mimer.kurs.uu.jdbc;2. import java.sql.*;3. public class JdbcOne {4. public static void main(String[] args) {5. try{6. Class.forName("com.mimer.jdbc.Driver");7. Connection con =

DriverManager.getConnection("jdbc:mimer:multi1","fredrik","fredrik");8. Statement stmt = con.createStatement();9. ResultSet rs = stmt.executeQuery("SELECT TABLE_NAME FROM

INFORMATION_SCHEMA.TABLES");10. while(rs.next()){11. System.out.println(rs.getString("TABLE_NAME"));12. }13. }14. catch(Exception e){15. System.out.println("Error:" + e.getMessage());16. }17. }18. }

More advanced example

1. package com.mimer.kurs.uu.jdbc;2. import java.sql.*;3. import java.io.*;4. public class JdbcTwo {5. public static void main(String[] args) {6. String driver="com.mimer.jdbc.Driver";7. String url="jdbc:mimer:multi1";8. String username="fredrik";9. String password="fredrik";10. ResultSet rs = null;11. PreparedStatement pstmt = null;12. Connection con = null;13. //All accessible tables for the current ident14. String query="SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE=?";15. try{16. Class.forName("com.mimer.jdbc.Driver");17. con = DriverManager.getConnection(url,username,password);18. pstmt = con.prepareStatement(query);19. pstmt.setString(1, "BASE TABLE");20. rs = pstmt.executeQuery();21. while(rs.next()){22. System.out.println(rs.getString("TABLE_NAME"));23. 24. }25. }

More advanced example, continued26. catch(ClassNotFoundException cnfe){27. System.out.println("Could not load Driver");28. }29. catch(SQLException sqle){30. System.out.println("SQL Error: " + sqle.getMessage());31. }32. catch(Exception e){33. System.out.println("Error:" + e.getMessage());34. }35. finally{36. try{37. rs.close();38. }39. catch(Exception e){40. }41. try{42. pstmt.close();43. }44. catch(Exception e){45. }46. try{47. con.close();48. }49. catch(Exception e){50. }51. }52. 53. }54. }

Assignment

1. Create a table in the database:create table PERSON(

PNR INTEGER,

NAME CHARACTER(10default 'Unknown',

SURNAME CHARACTER(10),

SEX CHARACTER(4) not null,

AGE INTEGER,

primary key(PNR));

Assignment

Create a simple Java program that adds persons to the database. It can be interactive or it can take all the

arguments on the commandline Tip: use PreparedStatement

Create a simple Java program that lists all persons older than a given age It can be interactive or it can take all the

arguments on the commandline Tip: use PreparedStatement