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法律研究如何编写一个JDBC程序来从多个数据库中提取数据？
要连接到数据库，您需要
注册驱动程序
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驱动程序类。
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
获取连接
通过将数据库的 URL、数据库中用户的用户名和密码（以字符串格式）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
next()
此方法返回一个布尔值，当结果集对象包含更多行时为真，不包含时为假。
getXXX()
这些方法用于检索每一行中的列值。如果特定列为整数类型，则需要使用 getInt() 方法，如果为字符串类型，则需要使用 getString() 方法。
//Executing the query
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();
}示例
假设我们在 Oracle 数据库中有一个名为 Student 的表，如下所示
NAME AGE PERCENTAGE -------------------------- Raju 19 85 Raja 17 67 Mukthar 18 79 David 19 90
以及一个在 MySQL 数据库中名为 Employee 的表，如下所示
+---------+--------+----------------+ | Name | Salary | Location | +---------+--------+----------------+ | Amit | 30000 | Hyderabad | | Kalyan | 40000 | Vishakhapatnam | | Renuka | 50000 | Delhi | | Archana | 15000 | Mumbai | +---------+--------+----------------+
以下 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{
//Registering the Driver
DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
//Getting the connection
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{
//Registering the Driver
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
//Getting the connection
String mysqlUrl = "jdbc:mysql://127.0.0.1/testdb";
Connection mySqlCon = DriverManager.getConnection(mysqlUrl, "root", "password");
System.out.println("Connected to MySQL database......");
return mySqlCon;
}
public void ExtractDataFromMySQL(Connection con) throws SQLException {
//Creating the Statement
Statement stmt = con.createStatement();
//Executing the query
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 {
//Creating the Statement
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();
//Connecting to Oracle
Connection oracleCon = obj.connectToOracle();
//Extracting data from Oracle
obj.ExtractDataFromOracle(oracleCon);
//Connecting to MySQL
Connection msqlCon = obj.connectToMySQL();
//Extracting data from MySQL
obj.ExtractDataFromMySQL(msqlCon);
}
}输出
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
更新于: 2019-07-30
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