Question

我在远程计算机（Ubuntu）上有一个MySQL数据库，我想通过本地计算机（Windows）访问。我知道这样做我GRANT可以访问我的MySQL用户。

GRANT ALL PRIVILEGES ON *.* TO 'user'@'%' IDENTIFIED BY 'password';

我正在使用JAVA JDBC来访问我的MySQL数据库。我能够执行INSERT查询，但SELECT查询返回一个空结果集。

public class MySqlConnector {

    Connection db;
    String user     = null;
    String password = null;
    String dbName   = null; 
    String componentsTable;

    public MySqlConnector(){
        this.user     = "user";     // MySQL Userid
        this.password = "password"; // MySQL Password
        this.dbName   = "database"; // Database Name
    }   

    public MySqlConnector(String dbName, String user, String password){
        if(dbName != null){
            this.dbName = dbName;
        }
        if(user != null){
            this.user = user;
        }
        if(password != null){
            this.password = password;
        }
    }

    public Connection getConnection(){
        try {
            // JDBC Driver
            Class.forName("com.mysql.jdbc.Driver").newInstance();
            System.out.println(dbName + " " + user + " " + password);
            db =    DriverManager.getConnection("jdbc:mysql://IPADDRESS:PORT/"+dbName,user,password);
            System.out.println("Connect Established");
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return db;
    }

    public void insertQuery(String query){
        Statement statement = null;
        try {
            statement = (Statement)db.createStatement();
            statement.executeUpdate(query);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public ResultSet executeQuery(String query){
        Statement statement= null;
        ResultSet resultset= null;
        try {
        statement = (Statement) db.createStatement();
        statement.executeQuery(query);
        resultset = statement.getResultSet ();

        } catch (SQLException e) {
            e.printStackTrace();
        }
        return resultset;
    }
    public void closeConnection() throws SQLException{
        db.close();
    }
}

在我查询时的servlet中

MySqlConnector mysql = new MySqlConnector();
mysql.getConnection();
mysql.insertQuery("INSERT INTO table_name VALUES(10)");
mysql.closeConnection();

工作得很漂亮。但是，executeQuery返回空。

MySqlConnector mysql = new MySqlConnector();
mysql.getConnection();
ResultSet result = mysql.executeQuery("SELECT * FROM table_name");
mysql.closeConnection();

我错过了什么建议或任何建议？

Answer 1

该错误出现在代码的其他部分，此处未列出。有两件事出了问题 -

会话变量初始化为null - 与NullPointerException
当我从ResultSet读取特定列时，我写了错误的列名，因此收到了非法访问权。

感谢大家查看我的问题并撰写答案/评论。

Answer 2

我认为Resultset查询必须是：

Resultset result = mysql.executeQuery("SELECT * FROM table_name");

Select在远程MySQL数据库上返回空结果

2 个答案: