第二个查询表示，resultset已关闭

Question

主要：

public static void main(String[] args) throws ClassNotFoundException, SQLException, InstantiationException, IllegalAccessException, InterruptedException {
                DatabaseConnectionHelper con = new DatabaseConnectionHelper();
                ResultSet rs = con.executeQuery("SELECT * FROM [winfiler].[dbo].[customer_data]");
                System.out.println(rs.next());
                while(rs.next()){
                    System.out.println(rs.getString("name"));
                }
                con.releaseResources();
                ResultSet rs3 = con.executeQuery("SELECT * FROM [winfiler].[dbo].[customer_data]");
                System.out.println(rs3.next());
                while(rs3.next()){
                    System.out.println(rs.getString("name"));
                }
    }

用于db连接的Helperclass：

public class DatabaseConnectionHelper {

    private Connection connection=null;
    private PreparedStatement statement=null;
    private ResultSet queryResult=null;

    public Connection connectToDatabase(){
        try {
            Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");
            connection = DriverManager.getConnection("jdbc:sqlserver://localhost:1433;databaseName=******;user=********;password=********");
            return connection;
        } catch (ClassNotFoundException ex) {
            MessageHelper.createClassNotFoundExceptionMessage("Eine exception ist aufgetreten", "Classe konnte nicht gefunden werden (Verbindung zur Datenbank)", ex.getMessage());
        } catch (SQLException ex) {
            MessageHelper.createSQLExceptionMessage("Eine exception ist aufgetreten", "Probleme beim der Datenabfrage - DatabaseConnectionHelper", ex.getMessage());
        }
            return null;
    }

    public ResultSet executeQuery(String query){
        try{
            statement = connectToDatabase().prepareStatement(query);
            queryResult = statement.executeQuery();


            return queryResult;
        }catch (SQLException ex) {
            MessageHelper.createSQLExceptionMessage("Eine exception ist aufgetreten", "Probleme beim der Datenabfrage - DatabaseConnectionHelper", ex.getMessage());
        }
        return null;
    }

    public boolean releaseResources(){
        try {
            this.queryResult.close();
            this.statement.close();
            this.connection.close();
            return true;
        } catch (SQLException ex) {
            MessageHelper.createSQLExceptionMessage("Eine exception ist aufgetreten", "Resourcen konnten nicht freigegeben werden - DatabaseConnectionHelper", ex.getMessage());
        }
        return false;
    }
}

Answer 1

实际的问题是在第二个循环中调用rs.getstring（“name”）；而不是rs3.getstring（“name”）；。

您的ConnectToDatabase()创建一个新连接。因此，只要不同时使用DBConnectionHelper，这就不是问题。

BTW1:您应该避免使用system.out(rs.next())；，因为这会产生副作用并跳过第一行。BTW2:您的releaseResources()可以改进：您应该忽略/单独捕捉来自RS和satement的异常，或者至少在finally中关闭连接本身。