在我们的 Java 程序中开始使用 PostgreSQL 之前，我们需要确保在机器上设置了 PostgreSQL JDBC 和 Java。您可以查看 Java 教程，了解如何在您的机器上安装 Java。现在让我们检查一下如何设置 postgresqljdbc 驱动程序。
从后面地址下载最新版本的postgresql-(version).jdbc.jar postgresql-jdbc 下载.
添加下载的 jar 文件 postgresql-(VERSION).jar，或者您可以将其与-classpath 选项一起使用，如下面的示例所示。
下面的部分假设您对 javajdbc 概念有所了解。如果没有，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。
下面的Java代码展示了如何连接到现有数据库。如果数据库不存在，那么将创建它，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");
}
}在编译和运行上述程序之前，请找到pg_hba.conf文件在PostgreSQL安装目录中创建一个文件，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，可以使用以下命令启动/重新启动postgres服务器：
现在，让我们编译并运行上面的程序来连接testdb。这里，我们使用postgres作为用户ID, 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。我们还假设当前版本的JDBC驱动程序postgresql-9.2-1002.jdbc3.jar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
下面的 Java 程序将用于在以前打开的数据库中创建一个表。请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，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
下面的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");
}
}在编译和执行上述程序时，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
下面的Java程序展示了我们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");
}
}当程序被编译和执行时，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
下面的Java代码展示了如何使用UPDATE语句更新任何记录，然后从我们的COMPANY表中获取并显示更新后的记录
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");
}
}当程序被编译和执行时，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
下面的Java代码展示了如何使用DELETE语句删除任何记录，然后从我们的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");
}
}当程序被编译和执行时，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