JDBCJava Database Connectivity

Jaroslav Porubän, Peter Václavík

2008-2014

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Introduction

Java API for accessing virtually any kind of tabular data

JDBC API is a Java interface for working with SQL

Establish a connection with a data source

Send queries and update statements to the data source

Process the results

Maydene Fisher, Jon Ellis, Jonathan Bruce: JDBC API Tutorial and Reference, 3rd Edition, Addison Wesley, 2003.

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JDBC Two-tier Model

DS

JDBC

Java ApplicationClient Machine

DS proprietary protocol

Database Server

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JDBC Three-tier Model

DS

JDBC

Java Application, Applet

or HTML BrowserClient Machine

DS proprietary protocol

Database Server

Application Server Server Machine (Business Logic)

HTTP, RMI, CORBA, or other calls

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JDBC Architecture

Java application

JDBC Driver Manager

JDBC API

JDBC Driver API

Data Source

JDBC – ODBC

ODBC

Native

driver

Native

driver

JDBC

driver

Data Source

Java JDBC

driver

Java JDBC

driver

Data Source Data Source

DB

MiddleWare

Type 1 Type 2 Type 3 Type 4

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Database URL

Used to make a connection to the databasejdbc:subprotocol_name:driver_dependant_dbname

Java DB (Derby)jdbc:derby://localhost/test

Oracle thin driverjdbc:oracle:thin:@localhost:1521:test

Pointbasejdbc:pointbase:server://localhost/test

MS SQLjdbc:jtds:sqlserver://localhost/test;tds=8.0

PostgreSQLjdbc:postgresql://localhost/test

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Loading a Driver

Import package java.sqlimport java.sql.*;

Load Driver ClassClass.forName("org.apache.derby.jdbc.ClientDriver");

Driver class must be in a runtime classpath JDBC 4 supports driver auto-loading

The Class.forName() method

loads a class dynamically into memory class itself creates an instance of the driver

object and registers it with the DriverManager

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Establishing a Connection

Making the Connection

String url =

"jdbc:derby://localhost/minesweeper";

String user = "minesweeper";

String password = "minesweeper";

Connection con = DriverManager.

getConnection(url, user, password);

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Creating a Table

Use SQL Statement to create a

table

String query = "CREATE TABLE student ("

+ "id INT PRIMARY KEY,"

+ "firstname VARCHAR(32) NOT NULL,"

+ "surname VARCHAR(32) NOT NULL)";

Statement stmt = con.createStatement();

stmt.executeUpdate(query);

stm.close();

Example: CreateTest.java

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Prepared Statements

The contained SQL is sent to the database and compiled or prepared beforehand

Depending on the DB engine, the SQL may be cached and reused even for a different PreparedStatement and most of the work is done by the DB engine rather than the driver

A PreparedStatement can take IN parameters, which act much like arguments to a method, for column values

PreparedStatement deal with data conversions that can be error prone in straight ahead, built on the fly SQL

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Inserting Data

Use SQL PreparedStatement to

insert row in a tableString query = "INSERT INTO student "

+ "(id, firstname, surname) "

+ "VALUES (?, ?, ?)";

PreparedStatement stmt =

con.prepareStatement(query);

stmt.setInt(1, 1);

stmt.setString(2, "John");

stmt.setString(3, "Singleton");

stmt.executeUpdate();

stmt.close(); Example: InsertTest.java

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Retrieving Values from Result Sets

Use SELECT to retrieve data from

databaseString query = "SELECT id, firstname, "

+ " surname FROM student";

Statement stmt = con.createStatement();

ResultSet rs = stmt.executeQuery(query);

while(rs.next()) {

System.out.printf("%4d %-32s %-32s",

rs.getInt(1), rs.getString(2),

rs.getString(3));

}

rs.close();

stmt.close(); Example: SelectTest.java

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Closing a Connection

Closing the Connection

Connection con = DriverManager.

getConnection(url, user, password);

Statement stmt = con.createStatement();

...

stm.close();

con.close();

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Java 7 try-with-resources

J7 makes our life easier with the try-with-resources statements:

try(Connection c = dataSource.getConnection()) {

try (Statement st = c.createStatement()) {

try(ResultSet rs

= st.executeQuery(“some query”)) {

//Do stuff with the rs

}

try(RestulSet rs

= st.executeQuery(“some query”) {

//Do stuff with the rs

}

}

}

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Java 7 try-with-resources

J7 makes our life easier with the try-with-resources statements (shorter):

try (Connection c = DriverManager

.getConnection(URL, USER, PASSWORD);

Statement st = c.createStatement();

ResultSet rs = st.executeQuery(DROP);

ResultSet rs2 = st.executeQuery(QUERY)) {

//do stuff, e.g. with rs and rs2

}

closes everything automatically!

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Result Set and Database metadata

Once you have the Connection or ResultSet objects, you can obtain the metadata about the database or the query

This gives valuable information about the database that you are using or data that you are retrieving

ResultSetMetaData rsmd = rs.getMetaData();

DatabaseMetaData dbmd =

connection.getMetaData();

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ResultSetMetaData

ResultSet rs = stmt.executeQuery(query);

ResultSetMetaData rsmd = rs.getMetaData();

int columnCount = rsmd.getColumnCount();

for (int i = 1; i <= columnCount; i++) {

System.out.println("Column Name: " + rsmd.getColumnName(i));

System.out.println("Column Type: " + rsmd.getColumnTypeName(i));

}

rs.close();

Example: RSMDTest.java