我查询H2数据库，得到一个Object类型的结果列表，我无法将它们转换为正确的格式：
iam查询的My VIEW表：
SELECT * FROM STATEMENTS_DATAPOINTS;
NAME DATA_POINTS_ID DATE F1 PRECISON RECALL
identifiedNeed 1 2017-11-19 0.3 0.5 0.2
identifiedNeed 2 2017-11-12 0.7 0.4 0.15
identifiedNeed 3 2017-11-15 0.5 0.3 0.1
identifiedNeed 4 2017-11-18 0.6 0.2 0.05
identifiedNeed 5 2017-11-13 0.1 0.2 0.05
identifiedNeed 6 2017-11-14 0.2 0.2 0.05
identifiedNeed 7 2017-11-16 0.4 0.2 0.05
identifiedBackground 8 2017-11-19 0.2 0.4 0.2
identifiedBackground 9 2017-11-12 0.4 0.3 0.15
identifiedBackground 10 2017-11-15 0.5 0.2 0.1
identifiedBackground 11 2017-11-18 0.6 0.1 0.05
identifiedBackground 12 2017-11-13 0.65 0.1 0.05
identifiedBackground 13 2017-11-14 0.77 0.1 0.05
identifiedBackground 14 2017-11-16 0.8 0.1 0.05
identifiedGoal 15 2017-11-19 0.1 0.4 0.2
identifiedGoal 16 2017-11-12 0.4 0.3 0.15
identifiedGoal 17 2017-11-15 0.3 0.2 0.1
identifiedGoal 18 2017-11-13 0.2 0.1 0.05
identifiedGoal 19 2017-11-12 0.5 0.2 0.15
identifiedGoal 20 2017-11-11 0.6 0.3 0.2
(20 rows, 2 ms)
我从一个java程序内部查询，得到的结果是：
[[Ljava.lang.Object;@328bbd7, [Ljava.lang.Object;@3a89e146, [Ljava.lang.Object;@340d5ed1, [Ljava.lang.Object;@14d6920b, [Ljava.lang.Object;@52667545, [Ljava.lang.Object;@27103d9e, [Ljava.lang.Object;@79b5147b]
这是表中的20个对象。我试过使用String()和Array()，但它们都不起作用，我该怎么办？我的目标是把所有这些要点都列在一个列表中。
具有查询方法的接口类：
public interface MeasurementRepository extends CrudRepository<Measurement, Long> {
@Query(value = "SELECT n" +
" measurement_point.daten" +
" , measurement_point.f1n" +
" , measurement_point.precisonn" +
" , measurement_point.recalln" +
"FROM measurement n" +
"LEFT JOIN measurement_data_points ON measurement.id = measurement_data_points.measurement_idn" +
"LEFT JOIN measurement_point ON measurement_data_points.data_points_id = measurement_point.id WHERE name='identifiedNeed';", nativeQuery = true)
List<Double> findAllMeasurementDataPoints();
我可以将List更改为String、Integer、Double、Objects类型，但我仍然得到相同的结果。
使用JdbcTemplate创建新类以查询：
public class DatabaseQueries {
@Autowired
JdbcTemplate jdbcTemplate;
public List<MeasurementPoint> findAllNeedDataPoints() {
List<MeasurementPoint> needStatementDataPoints = new ArrayList<>();
String query="SELECT measurement_point.date,measurement_point.f1, measurement_point.precison, measurement_point.recalln" +
"FROM measurement n" +
"LEFT JOIN measurement_data_points ON measurement.id = measurement_data_points.measurement_idn" +
"LEFT JOIN measurement_point ON measurement_data_points.data_points_id = measurement_point.id;";
List<Map<String, Object>> rows=jdbcTemplate.queryForList(query);
for(java.util.Map<String, Object> row :rows) {
MeasurementPoint measurementPoint = new MeasurementPoint();
measurementPoint.setDate((String)(row.get("DATE")));
measurementPoint.setF1((Double)(row.get("F1")));
measurementPoint.setPrecison((Double)(row.get("PRECISON")));
measurementPoint.setRecall((Double)(row.get("RECALL")));
needStatementDataPoints.add(measurementPoint);
}
return needStatementDataPoints;
}
}
我正在获取NullPointerException，它找不到任何值，我遗漏了什么吗？错误点：
List<Map<String, Object>> rows=jdbcTemplate.queryForList(query);
我现在得到的结果是：
[com.ibm.fk.textanalys.MeasurementPoint@58e52b28, com.ibm.fk.textanalys.MeasurementPoint@fa8c696, com.ibm.fk.textanalys.MeasurementPoint@5b06cf3c, com.ibm.fk.textanalys.MeasurementPoint@3d89bc9e, com.ibm.fk.textanalys.MeasurementPoint@4cc46c6c, com.ibm.fk.textanalys.MeasurementPoint@5919f14, com.ibm.fk.textanalys.MeasurementPoint@6883cfb5, com.ibm.fk.textanalys.MeasurementPoint@189ee377, com.ibm.fk.textanalys.MeasurementPoint@77d64b04, com.ibm.fk.textanalys.MeasurementPoint@7e3603d5, com.ibm.fk.textanalys.MeasurementPoint@8be95c1, com.ibm.fk.textanalys.MeasurementPoint@67d44afa, com.ibm.fk.textanalys.MeasurementPoint@221fb36f, com.ibm.fk.textanalys.MeasurementPoint@6cf92452, com.ibm.fk.textanalys.MeasurementPoint@1015a491, com.ibm.fk.textanalys.MeasurementPoint@55d3aff3, com.ibm.fk.textanalys.MeasurementPoint@a08faed, com.ibm.fk.textanalys.MeasurementPoint@2f76844a, com.ibm.fk.textanalys.MeasurementPoint@127a9c19, com.ibm.fk.textanalys.MeasurementPoint@5a9e0592]
现在得到的新结果：
[MeasurementPoint{f1=0.3, precison=0.5, recall=0.2, date='2017-11-19'}, MeasurementPoint{f1=0.7, precison=0.4, recall=0.15, date='2017-11-12'}, MeasurementPoint{f1=0.5, precison=0.3, recall=0.1, date='2017-11-15'}, MeasurementPoint{f1=0.6, precison=0.2, recall=0.05, date='2017-11-18'}, MeasurementPoint{f1=0.1, precison=0.2, recall=0.05, date='2017-11-13'}, MeasurementPoint{f1=0.2, precison=0.2, recall=0.05, date='2017-11-14'}, MeasurementPoint{f1=0.4, precison=0.2, recall=0.05, date='2017-11-16'}, MeasurementPoint{f1=0.2, precison=0.4, recall=0.2, date='2017-11-19'}, MeasurementPoint{f1=0.4, precison=0.3, recall=0.15, date='2017-11-12'}, MeasurementPoint{f1=0.5, precison=0.2, recall=0.1, date='2017-11-15'}, MeasurementPoint{f1=0.6, precison=0.1, recall=0.05, date='2017-11-18'}, MeasurementPoint{f1=0.65, precison=0.1, recall=0.05, date='2017-11-13'}, MeasurementPoint{f1=0.77, precison=0.1, recall=0.05, date='2017-11-14'}, MeasurementPoint{f1=0.8, precison=0.1, recall=0.05, date='2017-11-16'}, MeasurementPoint{f1=0.1, precison=0.4, recall=0.2, date='2017-11-19'}, MeasurementPoint{f1=0.4, precison=0.3, recall=0.15, date='2017-11-12'}, MeasurementPoint{f1=0.3, precison=0.2, recall=0.1, date='2017-11-15'}, MeasurementPoint{f1=0.2, precison=0.1, recall=0.05, date='2017-11-13'}, MeasurementPoint{f1=0.5, precison=0.2, recall=0.15, date='2017-11-12'}, MeasurementPoint{f1=0.6, precison=0.3, recall=0.2, date='2017-11-11'}]
public interface MeasurementRepository extends CrudRepository<Measurement, Long> {
@Query(value = "SELECT date, f1, precison, recall " +
"FROM measurement " +
"LEFT JOIN measurement_data_points ON measurement.id = measurement_data_points.measurement_id " +
"LEFT JOIN measurement_point ON measurement_data_points.data_points_id = measurement_point.id WHERE name='identifiedNeed';", nativeQuery = true)
List<Measurement> findAllMeasurementDataPoints();
}
但建议您使用JdbcTemplate进行查询，并将其与自定义映射器一起使用。jdbcTemplate.query(your_query, (rs, rowNumber) -> { ... your mapping here ... })
其中(rs，rowNumber)是RowMapper<T>接口的lambda表达式。
@Service
public class MeasurementRepository {
@Autowired
JdbcTemplate template;
public List<Measurement> findAllMeasurementDataPoints() {
template.query(your_query, (rs, rowNumber) -> {
Measurement measurement = new Measurement();
... your mapping here ....
return measurement;
})
}