PostgreSQL - 连接Java

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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。

  • 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。

连接数据库

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-

链接:https://www.learnfk.comhttps://www.learnfk.com/postgresql/postgresql-java.html

来源:LearnFk无涯教程网

# 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

创建表

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

插入操作

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-

无涯教程网

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

选择操作

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

更新操作

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

删除操作

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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