如何将 LinkedHashMap 转换为自定义 java 对象？
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how to convert LinkedHashMap to Custom java object?
提问by Lucas
I'm trying to get the data from one app to another via RESTful WS and it works, but I cannot use this data since I cannot cast it... WS returns a List of objects like this:
我正在尝试通过 RESTful WS 将数据从一个应用程序获取到另一个应用程序并且它可以工作，但是我无法使用此数据，因为我无法投射它...... WS 返回一个对象列表，如下所示：
{id=1, forename=John, surname=Bloggs, username=jbloggs, role=Graduate Developer, office=London, skills=[{technology=Java, experience=2.5}, {technology=Web, experience=2.0}, {technology=iOS, experience=0.0}, {technology=.NET, experience=0.0}]}
to get I it use Hymanson's ObjectMapper:
为了让我使用 Hymanson 的 ObjectMapper：
ObjectMapper mapper = new ObjectMapper();
List<ConsultantDto> list = new ArrayList<ConsultantDto>();
try {
list = mapper.readValue(con.getInputStream(), ArrayList.class);
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
after that I have 3 lines of code:
之后我有3行代码：
System.out.println(list.get(0));
System.out.println(list.get(0).getForename());
return list;
return because this method's return value is passed to other webservice which displays correct data in a browser. Interesting thing happens with two printing lines, one prints the data from the top of this post ({id:1 ... }) but the other one throws exception:
返回，因为此方法的返回值被传递给在浏览器中显示正确数据的其他 web 服务。有趣的事情发生在两条打印行上，一条从这篇文章的顶部 ({id:1 ... }) 打印数据，但另一条抛出异常：
java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.xxx.xxx.web.dto.rp.ConsultantDto
ConsultantDto and SkillDto are two legit classes which have all properties set to match the data from WS, all getters/setters are in place. As far as I'm concerned LinkedHashMap stores stuff as key:value pairs, so I just don't see where is this exception coming from. How can I fix it and why doesn't ObjectMapper just parse the value correctly (which it does when I get a single ConsultantDto rather than a List)?
ConsultantDto 和 SkillDto 是两个合法的类，它们的所有属性都设置为匹配来自 WS 的数据，所有 getter/setter 都已就位。就我而言，LinkedHashMap 将东西存储为键：值对，所以我只是不知道这个异常来自哪里。我该如何修复它，为什么 ObjectMapper 不正确解析值（当我得到一个 ConsultantDto 而不是 List 时它会这样做）？
采纳答案by Enno Shioji
You need to do this:
你需要这样做：
List<ConsultantDto> myObjects =
mapper.readValue(jsonInput, new TypeReference<List<ConsultantDto>>(){});
(From this SO answer)
（来自这个SO 答案）
The reason you have to use TypeReferenceis because of an unfortunate quirk of Java. If Java had a proper generics, I bet your syntax would have worked.
您必须使用的原因TypeReference是 Java 的一个不幸的怪癖。如果 Java 有合适的泛型，我敢打赌你的语法会奏效。
回答by Donald Choi
import:
进口：
import com.fasterxml.Hymanson.databind.ObjectMapper;
object:
目的：
private ObjectMapper mapper = new ObjectMapper();
examples:
例子：
PremierDriverInfoVariationDTO premierDriverInfoDTO =
mapper.convertValue(json, PremierDriverInfoVariationDTO.class);
log.debug("premierDriverInfoDTO : {}", premierDriverInfoDTO);
or
或者
Map<String, Boolean> map = mapper.convertValue(json, Map.class);
log.debug("result : {}", map);
assertFalse(map.get("eligiblePDJob"));
