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，我得到的是异常。让我知道，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

它正在代码下面写成json string。

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);      
    }

}

但是将json读取到Object失败了。输出：

{ “显示java.lang.NullPointerException”：{ “detailMessage”：NULL， “原因”：{ “显示java.lang.NullPointerException”：{ “$ ID”： “912da540-bf85-4e5d-869c-acfaebe85bdf”， “detailMessage”：空， “原因”： “912da540-bf85-4e5d-869c-acfaebe85bdf”， “堆栈跟踪”：空}}， “堆栈跟踪”：空}} com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException：无法识别的字段“$ id”（类java.lang.NullPointerException），而不是标记为可忽略的（3个已知属性：“cause”，“stackTrace”， “detailMessage”]）在[来源： { “显示java.lang.NullPointerException”：{ “detailMessage”：空， “原因”：{ “显示java.lang.NullPointerException”：{ “$标识”： “912da540-bf85-4e5d-869c-acfaebe85bdf”， “detailMessage” ：NULL， “原因”： “912da540-bf85-4e5d-869c-acfaebe85bdf”， “堆栈跟踪”：空}}， “堆栈跟踪”：空}}; line：1，column：107]（通过参考链： java.lang.NullPointerException [“$ id”]）at 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）

使用Jackson序列化Java异常

1 个答案: