java 对象映射器读取值

ObjectMapper readValue

提问by lg0173

I load a ressource file json with the text format

我用文本格式加载资源文件json

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

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

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

        }
    ]
}

I have a class with this properties prop1 and prop2

我有一个具有这个属性 prop1 和 prop2 的类

I want to recover with ObjectMapper a list class. What the method ?

我想用 ObjectMapper 恢复一个列表类。什么方法？

This code doesn't work ....

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>>(){});

Thanks for your help

谢谢你的帮助

回答by Yuriy Yunikov

In your case, I would write a custom JsonDeserializer. Haven't really tested the code, but I think the idea is clear:

在你的情况下，我会写一个自定义JsonDeserializer. 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);

And the code for JsonDeserializer:

和代码JsonDeserializer：

    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());
            ...
        }

        ...
    }

回答by SilverNak

First thing: Your JSON is invalid. There is a comma after the second object in the sourcesarray. This has to be deleted.

第一件事：您的 JSON 无效。sources数组中的第二个对象后面有一个逗号。这个必须删除。

Second: I think you didn't choose the right type for your result. What your JSON represents is a map which maps from string to an array of objects. So the type should be something like Map<String, Props[]>(Since you didn't provide the name of your class, I called it Props.

第二：我认为你没有为你的结果选择正确的类型。您的 JSON 代表的是从字符串映射到对象数组的映射。所以类型应该是这样的Map<String, Props[]>（因为你没有提供你的班级的名字，我把它叫做Props.

With these considerations you can construct a MapTypeby using ObjectMappers getTypeFactory()method and deserialize the value using the constructed type like shown below.

考虑到这些因素，您可以MapType使用ObjectMappersgetTypeFactory()方法构造 a并使用构造类型反序列化值，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);

回答by Essex Boy

I actually voted for the other answer, but this is my idea, to create the classes and let Hymanson do the work :

我实际上投票支持另一个答案，但这是我的想法，创建类并让 Hymanson 完成工作：

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;
    }

}

Output is:

输出是：

{"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'}]}