Deserializing stringified (quote enclosed) nested objects with Jackson

问题

I am consuming a "RESTful" service (via RestTemplate) that produces JSON as follows:

{
    "id": "abcd1234",
    "name": "test",
    "connections": {
        "default": "http://foo.com/api/",
        "dev": "http://dev.foo.com/api/v2"
    },
    "settings": {
        "foo": "{\n \"fooId\": 1, \"token\": \"abc\"}",
        "bar": "{\"barId\": 2, \"accountId\": \"d7cj3\"}"
    }
}

Note the settings.foo and settings.bar values, which cause issues on deserialization. I would like to be able to deserialize into objects (e.g., settings.getFoo().getFooId(), settings.getFoo().getToken()).

I was able to solve this specifically for an instance of Foo with a custom deserializer:

public class FooDeserializer extends JsonDeserializer<Foo> {
    @Override
    public Foo deserialize(JsonParser jp, DeserializationContext ctx) throws IOException {
        JsonNode node = jp.getCodec().readTree(jp);

        String text = node.toString();
        String trimmed = text.substring(1, text.length() - 1);
        trimmed = trimmed.replace("\\", "");
        trimmed = trimmed.replace("\n", "");

        ObjectMapper mapper = new ObjectMapper();
        JsonNode obj = mapper.readTree(trimmed);
        Foo result = mapper.convertValue(obj, Foo.class);

        return result;
    }
}

@Data
@JsonIgnoreProperties(ignoreUnknown = true)
public class Settings {
    @JsonDeserialize(using = FooDeserializer.class)
    private Foo foo;

    private Bar bar;
}

However, now if I want to deserialize settings.bar, I need to implement another custom deserializer. So I implemented a generic deserializer as follows:

public class QuotedObjectDeserializer<T> extends JsonDeserializer<T> implements ContextualDeserializer {
    private Class<?> targetType;
    private ObjectMapper mapper;

    public QuotedObjectDeserializer(Class<?> targetType, ObjectMapper mapper) {
        this.targetType = targetType;
        this.mapper = mapper;
    }

    @Override
    public JsonDeserializer<T> createContextual(DeserializationContext context, BeanProperty property) {
        this.targetType = property.getType().containedType(1).getRawClass();
        return new QuotedObjectDeserializer<T>(this.targetType, this.mapper);
    }

    @Override
    public T deserialize(JsonParser jp, DeserializationContext context) throws IOException {
        JsonNode node = jp.getCodec().readTree(jp);
        String text = node.toString();
        String trimmed = text.substring(1, text.length() - 1);
        trimmed = trimmed.replace("\\", "");
        trimmed = trimmed.replace("\n", "");

        JsonNode obj = this.mapper.readTree(trimmed);
        return this.mapper.convertValue(obj, this.mapper.getTypeFactory().constructType(this.targetType));
    }
}

Now I'm not sure how to actually use the deserializer, as annotating Settings.Foo with @JsonDeserialize(using = QuotedObjectDeserializer.class) obviously does not work.

Is there a way to annotate properties to use a generic custom deserializer? Or, perhaps more likely, is there a way to configure the default deserializers to handle the stringy objects returned in my example JSON?

Edit: The problem here is specifically deserializing settings.foo and settings.bar as objects. The JSON representation has these objects wrapped in quotes (and polluted with escape sequences), so they are deserialized as Strings.

回答1:

Sorry about the length of the code here. There are plenty of shortcuts here (no encapsulation; added e to defaulte to avoid keyword etc.) but the intent is there Model class:

package com.odwyer.rian.test;

import java.io.IOException;

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

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class Model {
    public String id;
    public String name;
    public Connections connections;
    public Settings settings;

    public static class Connections {
        public String defaulte;
        public String dev;

        @Override
        public String toString() {
            return ReflectionToStringBuilder.toString(this);
        }
    }

    public static class Foo {
        public Foo () {}

        @JsonCreator
        public static Foo create(String str) throws JsonParseException, JsonMappingException, IOException {
            return (new ObjectMapper()).readValue(str, Foo.class);
        }

        public Integer fooId;
        public String token;

        @Override
        public String toString() {
            return ReflectionToStringBuilder.toString(this);
        }
    }

    public static class Bar {
        public Bar() {}

        @JsonCreator
        public static Bar create(String str) throws JsonParseException, JsonMappingException, IOException {
            return (new ObjectMapper()).readValue(str, Bar.class);
        }

        public Integer barId;
        public String accountId;

        @Override
        public String toString() {
            return ReflectionToStringBuilder.toString(this);
        }
    }

    public static class Settings {
        public Foo foo;
        public Bar bar;

        @Override
        public String toString() {
            return ReflectionToStringBuilder.toString(this);
        }
    }

    @Override
    public String toString() {
        return ReflectionToStringBuilder.toString(this);
    }
}

The caller:

package com.odwyer.rian.test;

import java.io.File;
import java.io.IOException;
import java.util.Scanner;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

public class TestClass {
    private static ObjectMapper objectMapper = new ObjectMapper();

    public static void main(String[] args) throws JsonParseException, JsonMappingException, IOException {
        Scanner file = new Scanner(new File("test.json"));
        String jsonStr = file.useDelimiter("\\Z").next();

        Model model = objectMapper.readValue(jsonStr, Model.class);

        System.out.println(model.toString());
    }
}

The result (too much hassle to format out but it is all there!): com.odwyer.rian.test.Model@190083e[id=abcd1234,name=test,connections=com.odwyer.rian.test.Model$Connections@170d1f3f[defaulte=http://foo.com/api/,dev=http://dev.foo.com/api/v2],settings=com.odwyer.rian.test.Model$Settings@5e7e6ceb[foo=com.odwyer.rian.test.Model$Foo@3e20e8c4[fooId=1,token=abc],bar=com.odwyer.rian.test.Model$Bar@6291bbb9[barId=2,accountId=d7cj3]]]

The key, courtesy of Ted and his post (https://stackoverflow.com/a/8369322/2960707) is the @JsonCreator annotation

来源：https://stackoverflow.com/questions/37999824/deserializing-stringified-quote-enclosed-nested-objects-with-jackson