Installation
Before we start using PostgreSQL in our Java programs we need to make sure that we have PostgreSQL JDBC and Java set up on the machine. You can check Java tutorial for Java installation on your machine. Now let us check how to set up PostgreSQL JDBC driver.
Download latest version of postgresql-(VERSION).jdbc.jar from postgresql-jdbc repository.
Add downloaded jar file postgresql-(VERSION).jdbc.jar in your class path, or you can use it along with -classpath option as explained below in examples.
Following section assumes you have little knowledge about Java JDBC concepts. If you don’t, then it is suggested to spent half and hour with JDBC Tutorial to become comfortable with concepts explained below.
Connecting To Database
Following Java code shows how to connect to an existing database. If database does not exist, then it will be created and finally a database object will be returned.
import java.sql.Connection; import java.sql.DriverManager; public class PostgreSQLJDBC { public static void main(String args[]) { Connection c = null; try { Class.forName("org.postgresql.Driver"); c = DriverManager .getConnection("jdbc:postgresql://localhost:5432/testdb", "postgres", "123"); } catch (Exception e) { e.printStackTrace(); System.err.println(e.getClass().getName()+": "+e.getMessage()); System.exit(0); } System.out.println("Opened database successfully"); } }
Before you compile and run above program, find pg_hba.conf file in your PostgreSQL installation directory and add the following line:
# IPv4 local connections:
host all all 127.0.0.1/32 md5
You can start/restart postgres server in case it is not running using the following command:
[root@host]# service postgresql restart
Stopping postgresql service: [ OK ]
Starting postgresql service: [ OK ]
Now, let’s compile and run above program to get connection with testdb. Here, we are using postgres as user ID and 123 as password to access the database. You can change this as per your database configuration and setup. We are also assuming current version of JDBC driver postgresql-9.2-1002.jdbc3.jar is available in the current path
C:\JavaPostgresIntegration>javac PostgreSQLJDBC.java C:\JavaPostgresIntegration>java -cp c:\tools\postgresql-9.2-1002.jdbc3.jar;C:\JavaPostgresIntegration PostgreSQLJDBC Open database successfully
Create a Table
Following Java program will be used to create a table in previously opened database. Make sure you do not have this table already in your target database.
import java.sql.*; import java.sql.Connection; import java.sql.DriverManager; import java.sql.Statement; public class PostgreSQLJDBC { public static void main( String args[] ) { Connection c = null; Statement stmt = null; try { Class.forName("org.postgresql.Driver"); c = DriverManager .getConnection("jdbc:postgresql://localhost:5432/testdb", "manisha", "123"); System.out.println("Opened database successfully"); stmt = c.createStatement(); String sql = "CREATE TABLE COMPANY " + "(ID INT PRIMARY KEY NOT NULL," + " NAME TEXT NOT NULL, " + " AGE INT NOT NULL, " + " ADDRESS CHAR(50), " + " SALARY REAL)"; stmt.executeUpdate(sql); stmt.close(); c.close(); } catch ( Exception e ) { System.err.println( e.getClass().getName()+": "+ e.getMessage() ); System.exit(0); } System.out.println("Table created successfully"); } }
When program is compiled and executed, it will create COMPANY table in testdb database and will display the following two lines:
Opened database successfully
Table created successfully
INSERT Operation
Following Java program shows how we can create records in our COMPANY table created in above example:
import java.sql.Connection; import java.sql.DriverManager; import java.sql.Statement; public class PostgreSQLJDBC { public static void main(String args[]) { Connection c = null; Statement stmt = null; try { Class.forName("org.postgresql.Driver"); c = DriverManager .getConnection("jdbc:postgresql://localhost:5432/testdb", "manisha", "123"); c.setAutoCommit(false); System.out.println("Opened database successfully"); stmt = c.createStatement(); String sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) " + "VALUES (1, 'Paul', 32, 'California', 20000.00 );"; stmt.executeUpdate(sql); sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) " + "VALUES (2, 'Allen', 25, 'Texas', 15000.00 );"; stmt.executeUpdate(sql); sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) " + "VALUES (3, 'Teddy', 23, 'Norway', 20000.00 );"; stmt.executeUpdate(sql); sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) " + "VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 );"; stmt.executeUpdate(sql); stmt.close(); c.commit(); c.close(); } catch (Exception e) { System.err.println( e.getClass().getName()+": "+ e.getMessage() ); System.exit(0); } System.out.println("Records created successfully"); } }
When program compiled and executed, it will create given records in COMPANY table and will display the following two lines:
Opened database successfully
Records created successfully
SELECT Operation
Following Java program shows how we can fetch and display records from our COMPANY table created in above example:
import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.Statement; public class PostgreSQLJDBC { public static void main( String args[] ) { Connection c = null; Statement stmt = null; try { Class.forName("org.postgresql.Driver"); c = DriverManager .getConnection("jdbc:postgresql://localhost:5432/testdb", "manisha", "123"); c.setAutoCommit(false); System.out.println("Opened database successfully"); stmt = c.createStatement(); ResultSet rs = stmt.executeQuery( "SELECT * FROM COMPANY;" ); while ( rs.next() ) { int id = rs.getInt("id"); String name = rs.getString("name"); int age = rs.getInt("age"); String address = rs.getString("address"); float salary = rs.getFloat("salary"); System.out.println( "ID = " + id ); System.out.println( "NAME = " + name ); System.out.println( "AGE = " + age ); System.out.println( "ADDRESS = " + address ); System.out.println( "SALARY = " + salary ); System.out.println(); } rs.close(); stmt.close(); c.close(); } catch ( Exception e ) { System.err.println( e.getClass().getName()+": "+ e.getMessage() ); System.exit(0); } System.out.println("Operation done successfully"); } }
When program compiled and executed, it will produce the following result:
Opened database successfully ID = 1 NAME = Paul AGE = 32 ADDRESS = California SALARY = 20000.0 ID = 2 NAME = Allen AGE = 25 ADDRESS = Texas SALARY = 15000.0 ID = 3 NAME = Teddy AGE = 23 ADDRESS = Norway SALARY = 20000.0 ID = 4 NAME = Mark AGE = 25 ADDRESS = Rich-Mond SALARY = 65000.0 Operation done successfully
UPDATE Operation
Following Java code shows how we can use UPDATE statement to update any record and then fetch and display updated records from our COMPANY table:
import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.Statement; public class PostgreSQLJDBC { public static void main( String args[] ) { Connection c = null; Statement stmt = null; try { Class.forName("org.postgresql.Driver"); c = DriverManager .getConnection("jdbc:postgresql://localhost:5432/testdb", "manisha", "123"); c.setAutoCommit(false); System.out.println("Opened database successfully"); stmt = c.createStatement(); String sql = "UPDATE COMPANY set SALARY = 25000.00 where ID=1;"; stmt.executeUpdate(sql); c.commit(); ResultSet rs = stmt.executeQuery( "SELECT * FROM COMPANY;" ); while ( rs.next() ) { int id = rs.getInt("id"); String name = rs.getString("name"); int age = rs.getInt("age"); String address = rs.getString("address"); float salary = rs.getFloat("salary"); System.out.println( "ID = " + id ); System.out.println( "NAME = " + name ); System.out.println( "AGE = " + age ); System.out.println( "ADDRESS = " + address ); System.out.println( "SALARY = " + salary ); System.out.println(); } rs.close(); stmt.close(); c.close(); } catch ( Exception e ) { System.err.println( e.getClass().getName()+": "+ e.getMessage() ); System.exit(0); } System.out.println("Operation done successfully"); } }
When program compiled and executed, it will produce the following result:
Opened database successfully ID = 2 NAME = Allen AGE = 25 ADDRESS = Texas SALARY = 15000.0 ID = 3 NAME = Teddy AGE = 23 ADDRESS = Norway SALARY = 20000.0 ID = 4 NAME = Mark AGE = 25 ADDRESS = Rich-Mond SALARY = 65000.0 ID = 1 NAME = Paul AGE = 32 ADDRESS = California SALARY = 25000.0 Operation done successfully
DELETE Operation
Following Java code shows how we can use DELETE statement to delete any record and then fetch and display remaining records from our COMPANY table:
import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.Statement; public class PostgreSQLJDBC6 { public static void main( String args[] ) { Connection c = null; Statement stmt = null; try { Class.forName("org.postgresql.Driver"); c = DriverManager .getConnection("jdbc:postgresql://localhost:5432/testdb", "manisha", "123"); c.setAutoCommit(false); System.out.println("Opened database successfully"); stmt = c.createStatement(); String sql = "DELETE from COMPANY where ID=2;"; stmt.executeUpdate(sql); c.commit(); ResultSet rs = stmt.executeQuery( "SELECT * FROM COMPANY;" ); while ( rs.next() ) { int id = rs.getInt("id"); String name = rs.getString("name"); int age = rs.getInt("age"); String address = rs.getString("address"); float salary = rs.getFloat("salary"); System.out.println( "ID = " + id ); System.out.println( "NAME = " + name ); System.out.println( "AGE = " + age ); System.out.println( "ADDRESS = " + address ); System.out.println( "SALARY = " + salary ); System.out.println(); } rs.close(); stmt.close(); c.close(); } catch ( Exception e ) { System.err.println( e.getClass().getName()+": "+ e.getMessage() ); System.exit(0); } System.out.println("Operation done successfully"); } }
When program compiled and executed, it will produce the following result:
Opened database successfully ID = 3 NAME = Teddy AGE = 23 ADDRESS = Norway SALARY = 20000.0 ID = 4 NAME = Mark AGE = 25 ADDRESS = Rich-Mond SALARY = 65000.0 ID = 1 NAME = Paul AGE = 32 ADDRESS = California SALARY = 25000.0 Operation done successfully
转自:http://www.tutorialspoint.com/postgresql/postgresql_java.htm