JDBC操作MySQL数据库案例

JDBC操作MySQL数据库案例

 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.Statement;

 import org.junit.Test;

 public class JDBCTest {
     @Test
     public void test() throws Exception {
         Connection con = null;//定义引用
         Statement stmt = null;
         ResultSet rs = null;
         //规范的代码格式，try catch finally
         try {
             String driverClassName = "com.mysql.jdbc.Driver";
             String url = "jdbc:mysql://localhost:3306/exam";
             String username = "root";
             String password = "123";

             Class.forName(driverClassName);                                //加载
             con = DriverManager.getConnection(url, username, password);    //连接
             stmt = con.createStatement();                                //可以理解为创建SQL语句发射器

             //executeUpdate方法，可以执行增删改语句（INSERT, UPDATE, DELETE），返回被改变的记录条数
             String sql="DELETE FROM stu";
             int r = stmt.executeUpdate(sql);
             System.out.println("共删除了"+r+"条记录！");         

             //executeQuery方法，用于执行查询操作（SELECT），返回结果集
             String sql2="select * from emp";
             rs = stmt.executeQuery(sql2);
             while(rs.next()) {                            //把光标向下移动一行，并判断下一行是否存在！
                 int empno = rs.getInt(1);                //通过列编号来获取该列的值！
                 String ename = rs.getString("ename");    //通过列名称来获取该列的值
                 double sal = rs.getDouble("sal");
                 System.out.println(empno +  ", " + ename + ", " + sal);
             }
         } catch(Exception e) {
             throw new RuntimeException(e);
         } finally {
             // 一定要关闭！！！！！！
             if(rs != null) rs.close();
             if(stmt != null) stmt.close();
             if(con != null) con.close();
         }
     }
     @Test
     /**
      * 预处理方式
      * 优点：灵活，效率高，防SQL攻击
      * SQL攻击例子：
      *   若：sql = "select * from t_user where username='" + username + "' and password='" + password + "'";
      *   username = "a' or 'a'='a";
      *     password = "a' or 'a'='a";
      *     最后拼成的语句为：
      *  select * from t_user where username='a' or 'a'='a" and password='a' or 'a'='a'
      *  永远为true。
      */
     public void test2() throws Exception {
         Connection con = null;//定义引用
         ResultSet rs = null;
         PreparedStatement pstmt=null;
         try {
             String driverClassName = "com.mysql.jdbc.Driver";
             //mysql默认预处理是关闭的，加上这两个参数之后可以开启预处理
             String url = "jdbc:mysql://localhost:3306/exam?useServerPrepStmts=true&cachePrepStmts=true";
             String username = "root";
             String password = "123";
             Class.forName(driverClassName);
             con = DriverManager.getConnection(url, username, password);    

             String sql="select * from emp where empno=? and job=?";
             pstmt = con.prepareStatement(sql);
             pstmt.setInt(1, 1001);
             pstmt.setString(2, "文员");
             rs =pstmt.executeQuery();
             if(rs.next())
             {
                 System.out.println(rs.getString("ename"));
             }
         } catch(Exception e) {
             throw new RuntimeException(e);
         } finally {
             if(rs != null) rs.close();
             if(pstmt != null) pstmt.close();
             if(con != null) con.close();
         }
     }
 }