我有一个这种类型的列表List < HashMap < String, Object >> ResultSet
public List ResultSetToMap(ResultSet rs) throws SQLException {
ResultSetMetaData md = rs.getMetaData();
int columns = md.getColumnCount();
List<HashMap<String, Object>> list = new ArrayList<HashMap<String, Object>>();
while (rs.next()) {
row = new HashMap<String, Object>(columns);
for (int i = 1; i <= columns; ++i) {
row.put(md.getColumnName(i), rs.getObject(i));
}
list.add(row);
}
return list;
}
我想按“PROBABILITY”键的值对列表值进行排序。当我打印键及其值时,我得到了这个:
l_commitdate=1996-02-12
l_partkey=155190
PROBABILITY=56.63499683535207
l_commitdate=1996-02-28
l_partkey=67310
PROBABILITY=49.93142590485798
l_commitdate=1996-03-05
l_partkey=63700
PROBABILITY=56.88804620364059
l_commitdate=1996-03-30
l_partkey=2132
PROBABILITY=55.511179358539486
我想得到这个:
l_commitdate=1996-03-05
l_partkey=63700
PROBABILITY=56.88804620364059
l_commitdate=1996-02-12
l_partkey=155190
PROBABILITY=56.63499683535207
l_commitdate=1996-03-30
l_partkey=2132
PROBABILITY=55.511179358539486
l_commitdate=1996-02-28
l_partkey=67310
PROBABILITY=49.93142590485798
假设概率值是double类型:
list.sort((p1,p2)-> Double.compare( (double)p2.get("PROBABILITY"),(double) p1.get("PROBABILITY")));
看起来你知道你的ResultSet
中每一行的结构,所以如果你创建一个对象代表每一行而不是使用Map<String, Object>
,事情就会变得容易多了。我称之为Part
,因为这是关键所指的内容,但无论如何都要称之为有意义。
public class Part {
private LocalDate commitDate;
private long partKey;
private BigDecimal probability;
//getters and setters
}
有了这个你可以改变你的方法来返回一个Part
s列表(作为一个旁边:你不应该在这里使用无类型列表。即使你不遵循我的其他建议,你的方法签名应该始终有一个类型为正在返回的List
.Java方法名称也应该以小写字符开头 - 按照惯例,只有class
es的名称以大写字母开头)。
public List<Part> resultSetToParts(ResultSet rs) throws SQLException {
List<Part> list = new ArrayList<>(); //No need to specify the generic type again, we can use the diamond operator for Java 7 and later
while (rs.next()) {
Part part = new Part();
part.setCommitDate(rs.getDate("l_commitdate").toLocalDate()); //Note: this is vulnerable to NullPointerExceptions if the date can be null
part.setPartKey(rs.getString("l_partkey"));
part.setProbability(BigDecimal.valueOf(rs.getDouble("PROBABILITY")));
list.add(part);
}
return list;
}
既然我们已经完成了少量的工作来设置它,你可以在任何你想要的领域轻松地对它进行排序:
List<Part> parts = resultSetToParts(rs);
parts.sort(Comparator.comparing(Part::getProbability);