如何将LinkedHashMap转换为自定义java对象？ [英] how to convert LinkedHashMap to Custom java object?

问题描述

我正在尝试通过RESTful WS将数据从一个应用程序转移到另一个应用程序并且它可以工作，但我无法使用此数据，因为我无法转换它... WS返回一个像这样的对象列表：

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:

{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}]}

让我使用Jackson的ObjectMapper：

to get I it use Jackson's 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();

    }

之后我有3行代码：

System.out.println(list.get(0));
System.out.println(list.get(0).getForename());
return list;

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印刷线上，一条打印出来自这篇文章顶部的数据（{id：1 ...}），另一条则抛出异常：

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:

java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to com.xxx.xxx.web.dto.rp.ConsultantDto

ConsultantDto和SkillDto是两个合法的类，它们的所有属性都设置为与来自WS的数据相匹配，所有的getter / setter都已到位。就我而言，LinkedHashMap将东西存储为键：值对，所以我只是看不出这个异常的来源。我如何解决它，为什么ObjectMapper只是正确解析值（当我得到一个ConsultantDto而不是List时它会这样做？）

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)?

推荐答案

您需要这样做：

List<ConsultantDto> myObjects =
    mapper.readValue(jsonInput, new TypeReference<List<ConsultantDto>>(){});

（来自 SO回答）

你必须使用<$的原因c $ c> TypeReference 是因为Java的一个不幸的怪癖。如果Java有一个合适的泛型，我敢打赌你的语法会有效。

The reason you have to use TypeReference is because of an unfortunate quirk of Java. If Java had a proper generics, I bet your syntax would have worked.

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