我在数据库中查询两列,其中第一列是第二列的关键字。如何将结果列表转换为单个地图?可能吗?我刚刚看到了豆类的例子。
List<Map<String, Object>> steps = jdbcTemplate.queryForList("SELECT key, value FROM table");
// well this doesn't work
Map<String, String> result = steps.stream().collect(Collectors.toMap(s -> s.get("key"), s -> s.get("value")));
您忘记了将键和值映射转换为以下结果String
:
final Map<String, String> result = steps
.stream()
.collect(Collectors.toMap(s -> (String) s.get("key"), s -> (String) s.get("value")));
完整的例子
public static void main(String[] args) {
final List<Map<String, Object>> steps = queryForList("SELECT key, value FROM table");
final Map<String, String> result = steps
.stream()
.collect(Collectors.toMap(s -> (String) s.get("key"), s -> (String) s.get("value")));
result.entrySet().forEach(e -> System.out.println(e.getKey() + " -> " + e.getValue()));
}
private static List<Map<String, Object>> queryForList(String s) {
final List<Map<String, Object>> result = new ArrayList<>();
for (int i = 0; i < 10; i++) {
final Map<String, Object> map = new HashMap<>();
map.put("key", "key" + i);
map.put("value", "value" + i);
result.add(map);
}
return result;
}
哪些印刷品
key1 -> value1
key2 -> value2
key0 -> value0
key5 -> value5
key6 -> value6
key3 -> value3
key4 -> value4
key9 -> value9
key7 -> value7
key8 -> value8
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我来说两句