要连接数据库，您需要
选择所需的数据库，使用DriverManager类的registerDriver()方法或名为Class的类的forName()方法注册特定数据库的Driver类。
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
通过将数据库的URL，数据库中用户的用户名和密码（字符串格式）作为参数传递给DriverManager类的getConnection()方法，来创建连接对象。
Connection mysqlCon = DriverManager.getConnection(mysqlUrl, "root", "password");
并且，要提取数据，您需要执行select查询，如下所示：
ResultSet rs = stmt.executeQuery("Select * from Employee");要打印Result对象的内容，您需要使用ResultSet接口的以下方法：
此方法返回一个布尔值，当结果集对象包含更多行时为true，否则为false。
这些方法用于检索每一行中的列值。如果特定的列是整数类型，则需要使用方法getInt()；如果它是字符串类型，则需要使用method getString()。
//执行查询
ResultSet rs = stmt.executeQuery("Select *from Employee");
while(rs.next()) {
System.out.print("Name: "+rs.getString("Name")+", ");
System.out.print("Salary: "+rs.getInt("Salary")+", ");
System.out.print("City: "+rs.getString("Location"));
System.out.println();
}假设我们在Oracle数据库中有一个表名Student，如下所示：
NAME AGE PERCENTAGE -------------------------- Raju 19 85 Raja 17 67 Mukthar 18 79 David 19 90
在MySQL数据库中有一个名为Employee的表，如下所示：
+---------+--------+----------------+ | Name | Salary | Location | +---------+--------+----------------+ | Amit | 30000 | Hyderabad | | Kalyan | 40000 | Vishakhapatnam | | Renuka | 50000 | Delhi | | Archana | 15000 | Mumbai | +---------+--------+----------------+
按照JDBC程序提取这两个表的内容。
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class Multiple_DBs {
public Connection connectToOracle() throws SQLException{
//注册驱动程序
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
//获得连接
String oracleUrl = "jdbc:oracle:thin:@localhost:1521/xe";
Connection oracleCon = DriverManager.getConnection(oracleUrl, "system", "password");
System.out.println("Connected to Oracle database.....");
return oracleCon;
}
public Connection connectToMySQL() throws SQLException{
//注册驱动程序
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//获得连接
String mysqlUrl = "jdbc:mysql://localhost/testdb";
Connection mySqlCon = DriverManager.getConnection(mysqlUrl, "root", "password");
System.out.println("Connected to MySQL database......");
return mySqlCon;
}
public void ExtractDataFromMySQL(Connection con) throws SQLException {
//创建语句
Statement stmt = con.createStatement();
//执行查询
ResultSet rs = stmt.executeQuery("Select *from Employee");
System.out.println("Contents of Employee table in MySQL database: ");
while(rs.next()) {
System.out.print("Name: "+rs.getString("Name")+", ");
System.out.print("Salary: "+rs.getInt("Salary")+", ");
System.out.print("City: "+rs.getString("Location"));
System.out.println();
}
System.out.println();
}
public void ExtractDataFromOracle(Connection con) throws SQLException {
//创建语句
Statement stmt = con.createStatement();
ResultSet rs = stmt.executeQuery("Select *from Student");
System.out.println("Contents of student table in Oracle database: ");
while(rs.next()) {
System.out.print("Name: "+rs.getString("Name")+", ");
System.out.print("Age: "+rs.getInt("Age")+", ");
System.out.print("Percentage: "+rs.getString("Percentage"));
System.out.println();
}
System.out.println();
}
public static void main(String[] args) throws Exception {
Multiple_DBs obj = new Multiple_DBs();
//连接到Oracle-
Connection oracleCon = obj.connectToOracle();
//从Oracle提取数据
obj.ExtractDataFromOracle(oracleCon);
//连接到MySQL-
Connection msqlCon = obj.connectToMySQL();
//从MySQL提取数据
obj.ExtractDataFromMySQL(msqlCon);
}
}Connected to Oracle database..... Contents of student table in Oracle database: Name: Raju, Age: 19, Percentage: 85 Name: Raja, Age: 17, Percentage: 67 Name: Mukthar, Age: 18, Percentage: 79 Name: David, Age: 19, Percentage: 90 Connected to MySQL database...... Contents of Employee table in MySQL database: Name: Amit, Salary: 30000, City: Hyderabad Name: Kalyan, Salary: 40000, City: Vishakhapatnam Name: Renuka, Salary: 50000, City: Delhi Name: Archana, Salary: 15000, City: Mumbai