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法律研究如何編寫一個JDBC程式來從多個數據庫中提取資料？
要連線到資料庫，您需要
註冊驅動程式
選擇所需的資料庫，使用 **DriverManager** 類的 **registerDriver()** 方法或名為 Class 的類的 **forName()** 方法註冊特定資料庫的驅動程式類。
DriverManager.registerDriver(new com.mysql.jdbc.Driver());
獲取連線
透過將資料庫的 URL、資料庫中使用者的使用者名稱和密碼（以字串格式）作為引數傳遞給 **DriverManager** 類的 **getConnection()** 方法來建立連線物件。
Connection mysqlCon = DriverManager.getConnection(mysqlUrl, "root", "password");
並且，要提取資料，您需要執行 select 查詢，如下所示：
ResultSet rs = stmt.executeQuery("Select * from Employee");要列印 Result 物件的內容，您需要使用 ResultSet 介面的以下方法
next()
此方法返回一個布林值，當結果集物件包含更多行時為真，不包含時為假。
getXXX()
這些方法用於檢索每一行中的列值。如果特定列為整數型別，則需要使用 getInt() 方法，如果為字串型別，則需要使用 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
假設我們在 Oracle 資料庫中有一個名為 Student 的表，如下所示
NAME AGE PERCENTAGE -------------------------- Raju 19 85 Raja 17 67 Mukthar 18 79 David 19 90
以及一個在 MySQL 資料庫中名為 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 程式提取這兩個表的內容。
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:///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);
}
}輸出
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
更新於: 2019-07-30
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