ObjectMapper readValue

Question

我加载了文本格式的ressource文件json

{
    "sources": [{
            "prop1": "1",
            "prop2": "2"

        },
        {
            "prop1": "1",
            "prop2": "2"

        },
    ],
    "redirection": [{
            "prop1": "1",
            "prop2": "2"

        }
    ]
}

我有一个具有prop1和prop2属性的类

我想用ObjectMapper恢复一个list类。方法是什么？

此代码不起作用...

 Map<String, Object> mp =  mapper.readValue(jsonResource.getInputStream(),new TypeReference<Map<String, Object>>() {});
String sourceText= new ObjectMapper().readTree(jsonResource.getInputStream()).get("sources").asText();

 mapper.readValue(sourceText, new TypeReference<List<MyClass>>(){});

谢谢你的帮忙

Answer 1

在您的例子中，我会编写一个自定义的JsonDeserializer。我还没有真正测试过代码，但我认为这个想法很清楚：

    final MyClassDeserializer myClassDeserializer = new MyClassDeserializer();
    final SimpleModule deserializerModule = new SimpleModule();
    deserializerModule.addDeserializer(MyClass.class, myClassDeserializer);

    final ObjectMapper mapper = new ObjectMapper();
    mapper.registerModule(deserializerModule);

和JsonDeserializer的代码

    public class MyClassDeserializer extends JsonDeserializer<MyClass> {

    @Override
    public MyClass deserialize(final JsonParser jsonParser, final DeserializationContext context)
            throws IOException {
        final JsonNode node = jsonParser.getCodec().readTree(jsonParser);
        final JsonNode sourcesNode = node.get("sources");
        if(node.isArray()) {
            final ArrayNode arrayNode = (ArrayNode) node;
            final Iterable<JsonNode> nodes = arrayNode::elements;
            final Set<Source> set = StreamSupport.stream(nodes.spliterator(), false)
                    .map(mapper)
                    .collect(Collectors.toSet());
            ...
        }

        ...
    }

Answer 2

首先:您的JSON是无效的。在sources数组中的第二个对象之后有一个逗号。这必须被删除。

第二:我认为你没有为你的结果选择正确的类型。JSON表示的是一个从字符串映射到对象数组的映射。因此，类型应该类似于Map<String, Props[]> (因为您没有提供类的名称，所以我将其称为Props。

有了这些考虑，您可以使用ObjectMapper的getTypeFactory()方法构造一个MapType，并使用构造的类型反序列化该值，如下所示。

ObjectMapper mapper = new ObjectMapper();
TypeFactory typeFactory = mapper.getTypeFactory();
MapType mapType = typeFactory.constructMapType(HashMap.class, String.class, Props[].class);
Map<String, Props[]> map = mapper.readValue(s, mapType);

Answer 3

我实际上投票给了另一个答案，但这是我的想法，创建类并让jackson来做工作：

public class ResourceTest {

    @Test
    public void test1() throws IOException {
        assertTrue(true);

        Resource resource = new Resource();

        resource.getRedirectrions().add(makeRedirectrion("rprop11", "rprop12"));
        resource.getRedirectrions().add(makeRedirectrion("rprop21", "rprop22"));

        resource.getSources().add(makeSource("sprop11","sprop12"));
        resource.getSources().add(makeSource("sprop21","sprop22"));

        String json = new ObjectMapper().writeValueAsString(resource);
        System.out.println(json);

        Resource resource1 = new ObjectMapper().readValue(json, Resource.class);
        System.out.println(resource1);
    }

    private Source makeSource(String prop1, String prop2) {
        Source source = new Source();
        source.setProp1(prop1);
        source.setProp2(prop2);
        return source;
    }

    private Redirectrion makeRedirectrion(String prop1, String prop2) {
        Redirectrion redirectrion = new Redirectrion();
        redirectrion.setProp1(prop1);
        redirectrion.setProp2(prop2);
        return redirectrion;
    }

}

输出为：

{"sources":[{"prop1":"sprop11","prop2":"sprop12"},{"prop1":"sprop21","prop2":"sprop22"}],"redirectrions":[{"prop1":"rprop11","prop2":"rprop12"},{"prop1":"rprop21","prop2":"rprop22"}]}
Resource{sources=[Source{prop1='sprop11', prop2='sprop12'}, Source{prop1='sprop21', prop2='sprop22'}], redirectrions=[Source{prop1='rprop11', prop2='rprop12'}, Source{prop1='rprop21', prop2='rprop22'}]}