java - 如何使用 jackson objectmapper 反序列化

Question

我想将 json(如下所示)转换为 java 对象。我已经为 json 对象创建了 java 类，目前没有使用任何 jackson 注释。

import com.fasterxml.jackson.databind.ObjectMapper;

public class TestJunkie {

    private static final ObjectMapper objectMapper = new ObjectMapper();

    public static void main(String[] args) throws Exception {
        String json = "{\r\n" + 
                "   \"Info\":{\r\n" + 
                "       \"prop1\": \"value1\",\r\n" + 
                "       \"prop2\": \"value2\",\r\n" + 
                "       \"prop3\": \"value3\"\r\n" + 
                "   },\r\n" + 
                "   \"Data\":{\r\n" + 
                "       \"prop1\": \"value1\",\r\n" + 
                "       \"prop2\": \"value2\"\r\n" + 
                "   }\r\n" + 
                "}";

        Pack pack = objectMapper.readValue(json, Pack.class);
        System.out.println(pack);
    }

}

我将上面的 Json 对象转换为下面名为“Pack”的 Java 类:

import org.apache.commons.lang3.builder.ToStringBuilder;

public class Pack {

    private Info info;
    private Data data;

    public Info getInfo() {
        return info;
    }

    public void setInfo(Info info) {
        this.info = info;
    }

    public Data getData() {
        return data;
    }

    public void setData(Data data) {
        this.data = data;
    }

    @Override
    public String toString() {
        return new ToStringBuilder(this).append("info", info).append("data", data).toString();
    }

}

我故意省略了 Info 和 Data 类。它们的变量、getter、setter 与 json 匹配。如果您愿意，我可以将它们包括在内。

我收到以下异常。为什么会出现此异常以及如何修复它？

Exception in thread "main" com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "Info" (class com.tester.Jacksons.Pack), not marked as ignorable (2 known properties: "data", "info"])
 at [Source: (String)"{
    "Info":{
        "prop1": "value1",
        "prop2": "value2",
        "prop3": "value3"
    },
    "Data":{
        "prop1": "value1",
        "prop2": "value2"
    }
}"; line: 2, column: 10] (through reference chain: com.tester.Jacksons.Pack["Info"])
    at com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:60)
    at com.fasterxml.jackson.databind.DeserializationContext.handleUnknownProperty(DeserializationContext.java:822)
    at com.fasterxml.jackson.databind.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:1152)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownProperty(BeanDeserializerBase.java:1582)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownVanilla(BeanDeserializerBase.java:1560)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:294)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:151)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4001)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2992)
    at com.tester.Jacksons.TestJunkie.main(TestJunkie.java:22)

Answer 1

你的对象的键是小写的，在 json 中它们是大驼峰式的。如果这个命名方案是一致的，您可以在对象映射器上设置命名策略。

mapper.setPropertyNamingStrategy(PropertyNamingStrategy.UpperCamelCaseStrategy);