Java连接PostgreSQL数据库
Java连接到PostgreSQL数据库
以下Java代码显示如何连接到现有数据库。 如果数据库不存在，那么它将被创建，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：
# IPv4 local connections: host all all 127.0.0.1/32 md5 您可以启动/重新启动postgres服务器，使用以下命令运行：
[root@host]# service postgresql restart Stopping postgresql service: [ OK ] Starting postgresql service: [ OK ] 现在，我们来编译并运行上面的程序来获得与testdb的连接。 在这里使用用户ID为postgres和密码为123来访问数据库。 您可以根据数据库配置和设置进行更改。 我们还假定当前版本的JDBC驱动程序postgresql-9.2-1002.jdbc3.jar在当前路径中(c:\tools\)可用。
C:\JavaPostgresIntegration>javac PostgreSQLJDBC.java C:\JavaPostgresIntegration>java -cp c:\tools\postgresql-9.2-1002.jdbc3.jar;C:\JavaPostgresIntegration PostgreSQLJDBC Open database successfully 创建表
以下Java程序将用于在之前打开的数据库中创建一个表。确保目标数据库中没有此表。
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"); } } 编译和执行程序时，将在testdb数据库中创建COMPANY表，并显示以下两行：
Opened database successfully Table created successfully 插入数据操作
以下Java程序显示了如何在上述示例中创建的COMPANY表中创建/插入数据记录：
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, '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"); } } 程序编译执行后，将在COMPANY表中创建/插入给定的记录，并显示以下两行：
Opened database successfully Records created successfully SELECT操作
以下Java程序显示了如何从上述示例中创建的COMPANY表中获取和显示记录：
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"); } } 程序编译执行时，会产生以下结果：
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 更新操作
以下Java代码显示了如何使用UPDATE语句来更新指定记录，然后从COMPANY表中获取和显示更新的记录：
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"); } } 程序编译执行时，会产生以下结果：
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 删除操作
以下Java代码显示了如何使用DELETE语句删除指定记录，然后从COMPANY表中获取并显示剩余的记录：
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"); } } 程序编译执行时，会产生以下结果：
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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