使用Jackson处理自定义json中的"无法识别的令牌"异常

Question

我正在尝试使用Jackson json解析器(v2.5.2)来解析一个不是真正的json的自定义json文档,我无法弄清楚如何使它工作.我有一个json文档可能看起来像:

{
    "test": {
        "one":"oneThing",
        "two": nonStandardThing(),
        "three": true
    }
}

我想使用ObjectMapper将其映射到a java.util.Map,我只想nonStandardThing()在我的地图中为键添加为String值two.

当我通过它运行时,ObjectMapper.readValue(json, Map.class)我得到了异常:

com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'nonStandardThing': was expecting 'null', 'true', 'false' or NaN
 at [Source: { "test":{"test1":nonStandardThing(),"test2":"two"}}; line: 1, column: 35]
    at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:1487)
    at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:518)
    at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._reportInvalidToken(ReaderBasedJsonParser.java:2300)
    at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._reportInvalidToken(ReaderBasedJsonParser.java:2277)

我曾尝试注册a DeserializationProblemHandler,ObjectMapper但在发生此问题时从未调用过.

这是一个示例应用程序,显示了我尝试过的内容:

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonDeserializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.deser.DeserializationProblemHandler;
import java.io.IOException;
import java.util.Map;
import java.util.logging.Level;
import java.util.logging.Logger;

public class JacksonDeserializerTest {
    private Logger log = Logger.getLogger(JacksonDeserializerTest.class.getName());
    public JacksonDeserializerTest() {
        String validJson = "{ \"test\":{\"test1\":\"one\",\"test2\":\"two\"}}";
        String invalidJson = "{ \"test\":{\"test1\":nonStandardThing(),\"test2\":\"two\"}}";

        ObjectMapper mapper = new ObjectMapper();
        mapper.addHandler(new DeserializationProblemHandler() {
            @Override
            public boolean handleUnknownProperty(DeserializationContext dc, JsonParser jp, JsonDeserializer<?> jd, Object bean, String property) throws IOException, JsonProcessingException {
                System.out.println("Handling unknown property: " + property);
                return false;
            }
        });

        try {
            log.log(Level.INFO, "Valid json looks like: {0}", mapper.readValue( validJson, Map.class).toString());
            log.log(Level.INFO, "Invalid json looks like: {0}", mapper.readValue(invalidJson, Map.class).toString());
        } catch (IOException ex) {
            log.log(Level.SEVERE, "Error parsing json", ex);
        }

    }

    public static void main(String[] args) {
        JacksonDeserializerTest test = new JacksonDeserializerTest();
    }
}

输出如下:

Apr 24, 2015 1:40:27 PM net.acesinc.data.json.generator.jackson.JacksonDeserializerTest <init>
INFO: Valid json looks like: {test={test1=one, test2=two}}
Apr 24, 2015 1:40:27 PM net.acesinc.data.json.generator.jackson.JacksonDeserializerTest <init>
SEVERE: Error parsing json
com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'nonStandardThing': was expecting 'null', 'true', 'false' or NaN
 at [Source: { "test":{"test1":nonStandardThing(),"test2":"two"}}; line: 1, column: 35]
    at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:1487)
    at com.fasterxml.jackson.core.base.ParserMinimalBase._reportError(ParserMinimalBase.java:518)
    at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._reportInvalidToken(ReaderBasedJsonParser.java:2300)
    at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._reportInvalidToken(ReaderBasedJsonParser.java:2277)
    at com.fasterxml.jackson.core.json.ReaderBasedJsonParser._matchToken(ReaderBasedJsonParser.java:2129)

任何人都可以指出为什么处理程序永远不会被调用？或者,如果有一个更好的解析这个自定义json文档(杰克逊或不...),请告诉我.

Answer 1

未调用处理程序,因为无效部分不是property("two")而是值(nonStandardThing()).

处理此问题的一种显而易见的方法是将其nonStandardThing()作为a 传递,即将StringJSON文档重写为

{
    "test": {
        "one":"oneThing",
        "two": "nonStandardThing()",
        "three": true
    }
}

如果这不可能,那就没什么可做的了.使用自定义Jackson Deserializer仅对属性有用,而不是对值有用.