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Inizia a utilizzare PostgreSQL nel nostro programma Java Prima di tutto, dobbiamo assicurarci che PostgreSQL JDBC e Java siano installati sul nostro computer. Puoi controllare Java Tutorial, to learn how to install it on your machine Java. Now let's check how to set up the postgresqljdbc driver.
Download the latest version of postgresql-(version).jdbc.jar from the following address postgresql-jdbc Download.
Add the downloaded jar file postgresql-(VERSION).jar, or you can use it with the -classpath option as shown in the following example.
The following part assumes that you are familiar with the javajdbc concept. If not, it is recommended that you spend half an hour learning the JDBC tutorial to familiarize yourself with the concepts explained below.
The following Java code shows how to connect to an existing database. If the database does not exist, 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 compiling and running the above program, please find the pg_hba.conf file in the PostgreSQL installation directory, create a file, and add the following lines:
# IPv4 local connections: host all all all 127.0.0.1/32 md5
If the postgres server is not running, you can use the following command to start/restart the postgres server:
Now, let's compile and run the above program to connect to testdb. Here, we use postgres as the user ID 123 is used as the password to access the database. You can change it according to the database configuration and settings. We also assume that the current version of the 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 Database opened successfully
The following Java program will be used to create a table in the previously opened database. Make sure that there is no such table in the 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");
}
}While compiling and executing the program, it will create the COMPANY table in the testdb database and display the following two lines-
Database aperta con successo Table created successfully
The following Java program demonstrates how to create records in the COMPANY table created in the 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");
}
}While compiling and executing the above program, it will create the given record in the COMPANY table and display the following two lines-
Database aperta con successo Records created successfully
Il seguente programma Java mostra come ottenere e visualizzare i record dalla tabella COMPANY creata negli esempi precedenti
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("Operazione eseguita con successo");
}
}Quando il programma viene compilato ed eseguito, si ottiene il seguente risultato
Database aperta con successo 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 Operazione eseguita con successo
Esempio di codice Java che mostra come utilizzare l'istruzione UPDATE per aggiornare qualsiasi record e quindi ottenere e visualizzare i record aggiornati dalla nostra tabella COMPANY
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("Operazione eseguita con successo");
}
}Quando il programma viene compilato ed eseguito, si ottiene il seguente risultato
Database aperta con successo 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 Operazione eseguita con successo
Esempio di codice Java che mostra come utilizzare l'istruzione DELETE per eliminare qualsiasi record e quindi ottenere e visualizzare i record rimanenti dalla nostra tabella COMPANY
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("Operazione eseguita con successo");
}
}Quando il programma viene compilato ed eseguito, si ottiene il seguente risultato
Database aperta con successo 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 Operazione eseguita con successo