PostgreSQL - JAVA 接口

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安装

在我们开始在 Java 程序中使用 PostgreSQL 之前，我们需要确保机器上已设置 PostgreSQL JDBC 和 Java。您可以查看 Java 教程以了解您计算机上的 Java 安装。现在让我们看看如何设置 PostgreSQL JDBC 驱动程序。

• 从postgresql-jdbc存储库下载最新版本的postgresql-(VERSION).jdbc.jar。

• 将下载的 jar 文件postgresql-(VERSION).jdbc.jar添加到您的类路径中，或者您可以将其与 -classpath 选项一起使用，如下面示例中所述。

以下部分假设您对 Java JDBC 概念知之甚少。如果您没有，那么建议您花半个小时学习JDBC 教程，以熟悉下面解释的概念。

连接到数据库

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，则会创建数据库，最后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

如果 postgres 服务器没有运行，您可以使用以下命令启动/重新启动它 -

[root@host]# service postgresql restart
Stopping postgresql service:                               [  OK  ]
Starting postgresql service:                               [  OK  ]

现在，让我们编译并运行上面的程序来连接testdb。在这里，我们使用postgres作为用户 ID 和123作为密码来访问数据库。您可以根据您的数据库配置和设置更改此设置。我们还假设 JDBC 驱动程序postgresql-9.2-1002.jdbc3.jar的当前版本在当前路径中可用。

C:\JavaPostgresIntegration>javac PostgreSQLJDBC.java
C:\JavaPostgresIntegration>java -cp c:\tools\postgresql-9.2-1002.jdbc3.jar;C:\JavaPostgresIntegration PostgreSQLJDBC
Open database successfully

创建一个表

以下 Java 程序将用于在先前打开的数据库中创建一个表。确保您的目标数据库中还没有该表。

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");
   }
}

当程序编译并执行时，它将在testdb数据库中创建 COMPANY 表并显示以下两行 -

Opened database successfully
Table created successfully

插入操作

以下 Java 程序显示了如何在上面示例中创建的 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, '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");
   }
}

当上面的程序被编译并执行时，它将在 COMPANY 表中创建给定的记录，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面示例中创建的 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");
   }
}

当程序被编译并执行时，将产生以下结果 -

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");
   }
}

当程序被编译并执行时，将产生以下结果 -

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");
   }
}

当程序被编译并执行时，将产生以下结果 -

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