在无涯教程的Java程序中开始使用PostgreSQL之前,无涯教程需要确保在计算机上设置了PostgreSQL JDBC和Java。您可以检查Java教程以在计算机上安装Java。现在让无涯教程检查如何设置PostgreSQL JDBC驱动程序。
从 postgresql-jdbc 存储库。
在类路径中添加下载的jar文件 postgresql-(VERSION).jdbc.jar ,也可以将其与-classpath选项一起使用,如以下示例中所述。
以下Java代码显示了如何连接到现有数据库。如果数据库不存在,则将创建该数据库,最后将返回一个数据库对象。
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"); } }
在编译并运行上述程序之前,请在PostgreSQL安装目录中找到 pg_hba.conf 文件,并添加以下行-
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# IPv4 local connections: host all all 127.0.0.1/32 md5
您可以使用以下命令启动/重新启动postgres服务器,以防其未运行-
[root@host]# service postgresql restart Stopping postgresql service: [ OK ] Starting postgresql service: [ OK ]
现在,让无涯教程编译并运行以上程序以连接testdb。在这里,无涯教程使用 postgres 作为用户ID,并使用 123 作为密码来访问数据库。您可以根据数据库配置和设置进行更改。无涯教程还假设当前路径中提供了最新版本的JDBC驱动程序 postgresql-9.2-1002.jdbc3.jar 。
C:\JavaPostgresIntegration>javac PostgreSQLJDBC.java C:\JavaPostgresIntegration>java -cp c:\tools\postgresql-9.2-1002.jdbc3.jar;C:\JavaPostgresIntegration PostgreSQLJDBC Open database successfully
以下Java程序将用于在先前打开的数据库中创建表。
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"); } }
编译并执行程序时,它将在 testdb 数据库中创建COMPANY表,并将显示以下两行-
Opened database successfully Table created successfully
以下Java程序显示了如何在上示例中创建的COMPANY表中创建记录-
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, 'Learnfk', 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"); } }
编译并执行上述程序后,它将在COMPANY表中创建给定记录,并显示以下两行-
Opened database successfully Records created successfully
以下Java程序显示了如何从上示例中创建的COMPANY表中获取并显示记录-
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"); } }
编译并执行程序时,将产生以下输出-
Opened database successfully ID=1 NAME=Paul AGE=32 ADDRESS=California SALARY=20000.0 ID=2 NAME=Learnfk 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
以下Java代码显示了如何使用UPDATE语句更新任何记录,然后从COMPANY表中获取并显示更新的记录-
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"); } }
编译并执行程序时,将产生以下输出-
Opened database successfully ID=2 NAME=Learnfk 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
以下Java代码显示了如何使用DELETE语句删除任何记录,然后从COMPANY表中获取并显示剩余记录-
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"); } }
编译并执行程序时,将产生以下输出-
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
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