Java如何連線到資料庫（MySQL）？

如何使用JDBC連線到MySQL資料庫？ 假定資料庫名稱是：testdb，其中有一個表:employee，這個表中有4條記錄。

建立資料庫表的語句 -

use testdb;
create table if not exists employees (
  id int not null,
  age int not null,
  first varchar (255),
  last varchar (255)
);
INSERT INTO Employees VALUES (100, 28, 'Max', 'Su');
INSERT INTO Employees VALUES (101, 25, 'Wei', 'Wang');
INSERT INTO Employees VALUES (102, 30, 'Kida', 'Su');
INSERT INTO Employees VALUES (103, 28, 'Kobe', 'Bryant');

以下範例使用getConnection()，createStatement()和executeQuery()方法連線到資料庫並執行查詢。

package com.yiibai;

import java.sql.*;

public class JdbcConn {
    public static void main(String[] args) {
        String JDBC_DRIVER = "com.mysql.jdbc.Driver";
        String DB_URL = "jdbc:mysql://localhost/testdb?useSSL=false";
        String User = "root";
        String Passwd = "123456";
        try {
            Class.forName(JDBC_DRIVER);
        } catch (ClassNotFoundException e) {
            System.out.println("Class not found " + e);
        }
        int total_rows = 0;

        try {
            Connection con = DriverManager.getConnection(DB_URL, User, Passwd);
            Statement stmt = con.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM employees");
            while (rs.next()) {
                total_rows++;
            }
            System.out.println("There are " + total_rows + " records in the table");
        } catch (SQLException e) {
            System.out.println("SQL exception occured" + e);
        }
    }
}

上述程式碼範例將產生以下結果(結果可能會有所不同)。

There are 4 records in the table

註：如果JDBC驅動程式安裝不正確，將獲得ClassNotfound異常。

Class not found java.lang.ClassNotFoundException: com.mysql.jdbc.Driver
JDBC Class found
SQL exception occuredjava.sql.SQLException: No suitable driver found for jdbc:mysql://localhost/testdb