java - 我该如何解决这个 Java Jdbc 连接错误？

Question

我写了一个简单的Java Jdbc连接程序。我已经放置了 MySQL 连接器 jar。我还将类路径放在环境变量中。仍然无法解决此连接错误。

这是我的代码:

public class check {

    public static void main(String[] args) {

        System.out.println("-------- MySQL JDBC Connection Demo ------------");
        try
        {
            Class.forName("com.mysql.cj.jdbc.Driver");
        } 
        catch (ClassNotFoundException e) {
            System.out.println("MySQL JDBC Driver not found !!");
            return;
        }
        System.out.println("MySQL JDBC Driver Registered!");
        Connection connection = null;
        try {
            connection = DriverManager
                .getConnection("jdbc:mysql://localhost:3306/company","root","");
            System.out.println("SQL Connection to database established!");

        } catch (SQLException e) {
            System.out.println("Connection Failed! Check output console");
            return;
        } finally {
            try
            {
                if(connection != null)
                    connection.close();
                System.out.println("Connection closed !!");
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

输出:

-------- MySQL JDBC Connection Demo ----------
MySQL JDBC Driver Registered!
Connection Failed! Check output console
Connection closed !!

Answer 1

替换以下几行

} catch (SQLException e) {
    System.out.println("Connection Failed! Check output console");
    return;
}

与

} catch (SQLException e) {
    System.out.println("Connection Failed! Check output console");
    e.printStackTrace();
}

这样您就可以找到问题的根本原因。您当前的代码只是在吃掉这些重要信息。

附带说明，删除以下残留代码:

try
{
    Class.forName("com.mysql.cj.jdbc.Driver");
} 
catch (ClassNotFoundException e) {
    System.out.println("MySQL JDBC Driver not found !!");
    return;
}

Class.forName("com.mysql.cj.jdbc.Driver") 自 JDBC 4.0 以来不再需要。