java - 如何将 DBUtils 结果集转换为由更多领域对象组合而成的 JavaBeans？

Question

我正在 Spring Framework 中创建 MVC Web 应用程序，我需要将 Apache DBUtils 结果集中的行转换为由嵌套对象组成的 JavaBeans。

关于我发现的极少数示例，我创建了这个 RowProcessor 实现。

public class MonthOrderCountHandler extends BasicRowProcessor {

    @Override
    public Object toBean(ResultSet rs, Class type) throws SQLException {

        // Year
        Year year = new Year();
        year.setYearNo(rs.getInt("yearNo"));
        year.setYear4(rs.getString("year4"));
        year.setYear2(rs.getString("year2"));

        // Quarter
        Quarter quarter = new Quarter();
        quarter.setQuarter(rs.getInt("quarter"));

        // Month
        Month m = new Month();
        m.setYear(year);
        m.setQuarter(quarter);
        m.setMonthAbbreviation(rs.getString("monthAbbreviation"));
        m.setMonthName(rs.getString("monthName"));
        m.setMonthNo(rs.getInt("monthNo"));

        // Final bean
        MonthOrderCount result = new MonthOrderCount();
        result.setMonth(m);
        result.setOrderCount(rs.getInt("orderCount"));

        return result;

    }
}

问题:我想知道如何在我的 DAO 对象中使用这个行处理器，这个实现是否正确？

---

通常我以这种方式将行转换为 JavaBeans:

ResultSetHandler<List<MonthOrderCount>> listUrlHandler = new BeanListHandler<>(MonthOrderCount.class);

但在我的情况下，首先需要创建嵌套对象，然后创建最终的 JavaBean，因此我假设我需要自定义行处理器。

---

我的域对象的结构是:

MonthOrderCount 类:

public class MonthOrderCount {    
    private Month month;
    private int orderCount;
}

月级:

public class Month {
    private Quarter quarter;
    private Year year;
    private int monthNo;
    private String monthName;
    private String monthAbbreviation;
}

季度类(class):

public class Quarter {
    private int quarter;
    private String abbreviation;
}

年级:

public class Year {
    private int yearNo;
    private String year2;
    private String year4;
}

编辑: 我问是因为我的结果看起来像这样。 orderCount 变量已正确填充，但月份在所有情况下均为空。但对我来说最奇怪的是什么 - 从未调用 toBean() 方法。

2013-03-10 17:09:46 INFO ChartDataService:29 - [MonthOrderCount{month=null, orderCount=1863}, MonthOrderCount{month=null, orderCount=2262}, MonthOrderCount{month=null, orderCount=2531}, MonthOrderCount{month=null, orderCount=2379}, MonthOrderCount{month=null, orderCount=2106}, MonthOrderCount{month=null, orderCount=1498}, MonthOrderCount{month=null, orderCount=1300}, MonthOrderCount{month=null, orderCount=1578}, MonthOrderCount{month=null, orderCount=2385}, MonthOrderCount{month=null, orderCount=2991}, MonthOrderCount{month=null, orderCount=2219}, MonthOrderCount{month=null, orderCount=1943}, MonthOrderCount{month=null, orderCount=264}]

Answer 1

如果要将结果集转换为 JavaBeans 列表，则需要覆盖 toBeanList() 而不是 toBean() 方法。

重写 BasicRowProcessor 的最终处理程序类如下所示:

public class MonthOrderCountHandler extends BasicRowProcessor {

    @Override
    public List toBeanList(ResultSet rs, Class clazz) {
        try {
            List newlist = new LinkedList();
            while (rs.next()) {
                newlist.add(toBean(rs, clazz));
            }
            return newlist;
        } catch (SQLException ex) {
            throw new RuntimeException(ex);
        }
    }

    @Override
    public Object toBean(ResultSet rs, Class type) throws SQLException {

        // Year
        Year year = new Year();
        year.setYearNo(rs.getInt("yearNo"));
        year.setYear4(rs.getString("year4"));
        year.setYear2(rs.getString("year2"));

        // Quarter
        Quarter quarter = new Quarter();
        quarter.setQuarterNo(rs.getInt("quarterNo"));

        // Month
        Month m = new Month();
        m.setYear(year);
        m.setQuarter(quarter);
        m.setMonthAbbreviation(rs.getString("monthAbbreviation"));
        m.setMonthName(rs.getString("monthName"));
        m.setMonthNo(rs.getInt("monthNo"));

        // Final bean
        MonthOrderCount result = new MonthOrderCount();
        result.setMonth(m);
        result.setOrderCount(rs.getInt("orderCount"));

        return result;

    }
}

希望对大家有帮助。