使用 Jackson 序列化 Java 异常 [重复]

Question

package com.dh.inheritance;

import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;


public class Client6{

    public static void main(String[] args){

        ObjectMapper objectMapper = new ObjectMapper();
        objectMapper.enableDefaultTyping(); 
        objectMapper.enableDefaultTyping(ObjectMapper.DefaultTyping.NON_FINAL, JsonTypeInfo.As.WRAPPER_OBJECT);         
        objectMapper.setVisibility(PropertyAccessor.SETTER, JsonAutoDetect.Visibility.NONE);
        objectMapper.setVisibility(PropertyAccessor.GETTER, JsonAutoDetect.Visibility.NONE);
        objectMapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);
        objectMapper.setVisibility(PropertyAccessor.IS_GETTER, JsonAutoDetect.Visibility.NONE);         
        objectMapper.configure(SerializationFeature.WRITE_NULL_MAP_VALUES, true);
        objectMapper.configure(SerializationFeature.FAIL_ON_SELF_REFERENCES, true);

        try {

            String test = null;
            test.length();

        } catch (Exception e) {

            try {
                String jsonString = objectMapper.writeValueAsString(e);
                System.out.println(jsonString);
            } catch (JsonProcessingException e1) {
                e1.printStackTrace();
            }
        }
    }   

}

当我执行上面的代码时，我遇到了异常。请告诉我，如何解决这个问题。

com.fasterxml.jackson.databind.JsonMappingException: Direct self-reference leading to cycle (through reference chain: java.lang.NullPointerException["cause"])
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:230)
    at com.fasterxml.jackson.databind.ser.BeanPropertyWriter._handleSelfReference(BeanPropertyWriter.java:879)
    at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:666)
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:678)
    at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeWithType(BeanSerializerBase.java:569)
    at com.fasterxml.jackson.databind.ser.impl.TypeWrappedSerializer.serialize(TypeWrappedSerializer.java:32)
    at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:130)
    at com.fasterxml.jackson.databind.ObjectMapper._configAndWriteValue(ObjectMapper.java:3613)
    at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:2980)
    at com.dh.inheritance.Client6.main(Client6.java:33)

Answer 1

它在以下代码中工作，用于编写为 json 字符串。

objectMapper.registerModule(new MyModule());

package com.dh.inheritance;

import com.fasterxml.jackson.annotation.JsonIdentityInfo;
import com.fasterxml.jackson.annotation.ObjectIdGenerators;


public abstract class MixIn {

    @JsonIdentityInfo(generator=ObjectIdGenerators.StringIdGenerator.class, property="$id")
    private Throwable cause;

}

package com.dh.inheritance;

import com.fasterxml.jackson.core.Version;
import com.fasterxml.jackson.databind.module.SimpleModule;

public class MyModule extends SimpleModule{

    public MyModule() {
        super("test", new Version(2, 7, 2, null));
    }

    @Override
    public void setupModule(SetupContext context) {
        context.setMixInAnnotations(Throwable.class, MixIn.class);      
    }

}

但是读取 json 到 Object 失败了。 输出：

{"java.lang.NullPointerException":{"detailMessage":null,"cause":{"java.lang.NullPointerException":{"$id":"912da540-bf85-4e5d-869c-acfaebe85bdf", "detailMessage":null,"cause":"912da540-bf85-4e5d-869c-acfaebe85bdf","stackTrace":null}},"stackTrace":null}} com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException： 无法识别的字段“$id”（类 java.lang.NullPointerException），不是 标记为可忽略（3 个已知属性：“cause”、“stackTrace”、 "detailMessage"]) 在 [来源： {"java.lang.NullPointerException":{"detailMessage":null,"cause":{"java.lang.NullPointerException":{"$id":"912da540-bf85-4e5d-869c-acfaebe85bdf","detailMessage" :null,"cause":"912da540-bf85-4e5d-869c-acfaebe85bdf","stackTrace":null}},"stackTrace":null}};行：1，列：107]（通过引用链： java.lang.NullPointerException["$id"]) 在 com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:62) 在 com.fasterxml.jackson.databind.DeserializationContext.reportUnknownProperty(DeserializationContext.java:855) 在 com.fasterxml.jackson.databind.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:1083) 在 com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownProperty(BeanDeserializerBase.java:1389) 在 com.fasterxml.jackson.databind.deser.std.ThrowableDeserializer.deserializeFromObject(ThrowableDeserializer.java:135) 在 com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:133) 在 com.fasterxml.jackson.databind.jsontype.impl.AsWrapperTypeDeserializer._deserialize(AsWrapperTypeDeserializer.java:115) 在 com.fasterxml.jackson.databind.jsontype.impl.AsWrapperTypeDeserializer.deserializeTypedFromObject(AsWrapperTypeDeserializer.java:49) 在 com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeWithType(BeanDeserializerBase.java:1017) 在 com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:488) 在 com.fasterxml.jackson.databind.deser.std.ThrowableDeserializer.deserializeFromObject(ThrowableDeserializer.java:104) 在 com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:133) 在 com.fasterxml.jackson.databind.jsontype.impl.AsWrapperTypeDeserializer._deserialize(AsWrapperTypeDeserializer.java:115) 在 com.fasterxml.jackson.databind.jsontype.impl.AsWrapperTypeDeserializer.deserializeTypedFromObject(AsWrapperTypeDeserializer.java:49) 在 com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeWithType(BeanDeserializerBase.java:1017) 在 com.fasterxml.jackson.databind.deser.impl.TypeWrappedDeserializer.deserialize(TypeWrappedDeserializer.java:42) 在 com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3789) 在 com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2779) 在 com.dh.inheritance.Client6.main(Client6.java:45)