Mysql数据库异常 [英] Mysql database Exception

问题描述

线程"main"中的异常java.lang.Error:未解决的编译问题:类型不匹配:无法从java.sql.Statement转换为com.mysql.jdbc.Statement

我是Java的初学者，我正在尝试使用mysql数据库，我已经从mysql.com下载了mysql-connector-java-5.1.23-bin.jar文件，并且已将此jar文件添加到我的构建路径中我的项目，但以下代码中有错误线程"main"中的异常java.lang.Error:未解决的编译问题:类型不匹配:无法从java.sql.Statement转换为com.mysql.jdbc.Statement

---

package com.example.demo;

import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;

import com.mysql.jdbc.Connection;
import com.mysql.jdbc.Statement;

public class DBConnect
{
private static final String userName = "root";
private static final String userpwd = "sverma";
private static final String CONN_STR = "jdbc:mysql://localhost:3306/phpweb_db";

public static void main(String[] args) throws SQLException
{

    Connection conn = null;
    Statement st = null;
    ResultSet rs = null;

    try
    {
        DriverManager.getConnection(CONN_STR, userName, userpwd);
        st=conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_READ_ONLY);
        rs = st.executeQuery("select * from user");
        rs.last();
        System.out.println("No of rows: " + rs.getRow());

        // System.out.println("Connected Successfully...");
    }
    catch (SQLException e)
    {
        System.err.println(e);

    }
    finally
    {
        if (rs != null)
        {
            rs.close();
        }
        if (st != null)
        {
            st.close();
        }
        if (conn != null)
        {
            conn.close();
        }
    }
}

}

推荐答案

错误的类

import com.mysql.jdbc.Connection;
import com.mysql.jdbc.Statement;

应该是

import java.sql.Connection;
import java.sql.Statement;

---

实际上，java将所有内容与特定的数据库引擎分离.永远都不需要导入MySQL(或ProgressSQL或...)类.

---

In fact, java decouples everything from a specific database engine. One never should need an import of MySQL (or ProgressSQL or ...) classes.

要在运行时提供这些类，在获得连接之前， try 之后的第一件事是:

To have those classes available at run-time, the first thing after the try, before getting the connection would be:

Class.forName("com.mysql.jdbc.Driver");

该技术将允许从配置文件读取所有字符串，并编写独立于数据库的代码.

This technique would allow reading all strings from a configuration file, and writing database independent code.

缺少:conn = ...

Missing: conn = ...

conn = DriverManager.getConnection(CONN_STR, userName, userpwd);

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