Question

我的网络服务遇到了逻辑错误。它返回0而不是返回总价格。这是因为它要求我的代码底部的另一个return语句，是否存在此错误？在此先感谢您的帮助

public int checkPart(java.lang.String partname, int quantity) throws ClassNotFoundException, SQLException {
    try {
        Class.forName("com.mysql.jdbc.Driver");
        Connection con = DriverManager.getConnection("jdbc:mysql://ConnectionString);
        Statement st = con.createStatement();
        ResultSet rs = st.executeQuery("SELECT PartName, Price, Quantity FROM parts WHERE PartName =" + partname + ";");
        while (rs.next()) {
            int PriceVar = rs.getInt(1);
            int total = PriceVar * rs.getInt(2);
            return total;
        }
        rs.close();
        return 0;
    } 
    catch (ClassNotFoundException ex) {
        Logger.getLogger(WarehouseWebService.class.getName()).log(Level.SEVERE, null, ex);
    }
    catch (SQLException ex) {
        Logger.getLogger(WarehouseWebService.class.getName()).log(Level.SEVERE, null, ex);
    }
    return 0;

Answer 1

试试这种格式。

int total = 0;
Connection con = null;
try {
    Class.forName("com.mysql.jdbc.Driver");
    con = DriverManager.getConnection("jdbc:mysql://ConnectionString");
    // ...
    if (rs.next()) {
        int PriceVar = rs.getInt(1);
        total = PriceVar * rs.getInt(2);
    }
    rs.close();
} catch (ClassNotFoundException ex) {
    Logger.getLogger(WarehouseWebService.class.getName()).log(Level.SEVERE, null, ex);
} catch (SQLException ex) {
    Logger.getLogger(WarehouseWebService.class.getName()).log(Level.SEVERE, null, ex);
} finally {
    if (con != null) {
        con.close();
    }
}
return total;

Answer 2

你最好在一段时间内添加休息时间以获得第一个结果：

int total = 0;
Connection con = null;
try {
    Class.forName("com.mysql.jdbc.Driver");
    con = DriverManager.getConnection("jdbc:mysql://ConnectionString");
    // ...
    if (rs.next()) {
        int PriceVar = rs.getInt(1);
        total = PriceVar * rs.getInt(2);
        break; // get first one
    }
    rs.close();
} catch (ClassNotFoundException ex) {
    Logger.getLogger(WarehouseWebService.class.getName()).log(Level.SEVERE, null, ex);
} catch (SQLException ex) {
    Logger.getLogger(WarehouseWebService.class.getName()).log(Level.SEVERE, null, ex);
} finally {
    if (con != null) {
        con.close();
    }
}
return total;

Answer 3

使用 SQL 的sum()功能代替执行此操作

SELECT SUM(price) FROM table_name;

这将从您的表 table_name

中显示价格列的返还金额

修改

ResultSet rs = st.executeQuery("SELECT SUM(Price) FROM parts WHERE PartName =" + partname + ";");

P.S 采取这个概念，不要只是复制粘贴查询。它可能有不包括撇号的问题。 :-)

Answer 4

首先，您的查询不正确（您确实应该绑定参数）。简短的回答，改变这个

WHERE PartName =" + partname + ";");

到

WHERE PartName ='" + partname + "';"); // <-- single quotes.

但是，我认为你真的想要（使用try-with-resources来清理）

public int checkPart(String name, int quantity)
        throws ClassNotFoundException, SQLException {
    Class.forName("com.mysql.jdbc.Driver");
    String url = "jdbc:mysql://ConnectionString";
    String sql = "SELECT Price FROM parts WHERE PartName=?";
    try (Connection con = DriverManager.getConnection(url);
            PreparedStatement ps = con.prepareStatement(sql)) {
        ps.setString(1, name);
        ResultSet rs = ps.executeQuery();
        if (rs.next()) {
            return rs.getInt(1);
        }
    }
    throw new SQLException(String.format("No PartName={%s} Found", name));
}

Answer 5

当这种情况声明一个局部变量并最后返回它时。尽量避免一次返回它会造成混乱。你可以使用sql的sum方法，你可以很容易地得到所有的总和，你可以避免循环。

使用JDBC连接循环时出现Java逻辑错误

5 个答案: