没有使用Jackson进行堆栈跟踪的序列化/反序列化异常

Question

我正在尝试创建一个将java.lang.Exception存储为字段的类。我也尝试使用@JsonIgnoreProperties注释从堆栈化/反序列化中排除堆栈跟踪。

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.IOException;

class ExWrapper {
    @JsonIgnoreProperties({"stackTrace"})
    public Exception ex;

    @Override
    public String toString() {
        return "ExWrapper{" +
                "ex=" + ex +
                '}';
    }
}

public class Example {
    public static void main(String[] args) throws IOException {
        ObjectMapper mapper = new ObjectMapper();
        ExWrapper exw = new ExWrapper();
        exw.ex = new Exception("Oops");
        String str = mapper.writeValueAsString(exw);
        System.out.println(str);
        ExWrapper exW = mapper.readValue(str, ExWrapper.class);
        System.out.println(exW);
    }
}

结果错误非常令人惊讶，杰克逊找不到message字段：

Exception in thread "main" com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "message" (class java.lang.Exception), not marked as ignorable (one known property: "cause"])
 at [Source: (String)"{"ex":{"cause":null,"message":"Oops","suppressed":[],"localizedMessage":"Oops"}}"; line: 1, column: 32] (through reference chain: ExWrapper["ex"]->java.lang.Exception["message"])
    at com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:61)
    at com.fasterxml.jackson.databind.DeserializationContext.handleUnknownProperty(DeserializationContext.java:840)
    at com.fasterxml.jackson.databind.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:1179)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownProperty(BeanDeserializerBase.java:1592)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownVanilla(BeanDeserializerBase.java:1570)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:375)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159)
    at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:138)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:288)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:151)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4202)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3205)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3173)
    at Example.main(Example.java:25)

[嗯，在getMessage类中只有setMessage，没有Throwable，因此，除非您尝试删除@JsonIgnoreProperties批注，否则这似乎有点合理。它的工作原理就像一种魅力：它可以正确地序列化和反序列化，并且缺少message的setter突然不是问题。将"message"添加到忽略的字段也会使其起作用（但没有异常消息）。

我试图使用调试器随机插入Jackson代码，发现缺少@JsonIgnoreProperties时，最终会调用ThrowableDeserializer方法，而当存在注释时就不会调用它们。 ThrowableDeserializer似乎有一些针对异常消息的技巧。我的猜测是，当缺少堆栈跟踪并且Jackson退回到默认的Java Bean序列化程序时，ThrowableDeserializer不可行。

问题是这里到底发生了什么以及如何解决。

Answer 1

版本2

ThrowableDeserializer类扩展了BeanDeserializer，因此这两个共享一些代码来创建和反序列化POJO。 Exception不是常规的POJO，应以不同的方式处理。由于它没有提供给很多设置器，因此我们需要使用构造函数来创建带有消息和其他可以跳过的字段的设置器。要注册构造函数，我们可以使用MixIn功能：

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;

import java.io.File;

public class JsonPathApp {

    public static void main(String[] args) throws Exception {
        File jsonFile = new File("./resource/test.json").getAbsoluteFile();

        ObjectMapper mapper = new ObjectMapper();
        mapper.addMixIn(Exception.class, ExceptionMixIn.class);
        mapper.addMixIn(Throwable.class, ThrowableMixIn.class);

        ExWrapper exW = mapper.readValue(jsonFile, ExWrapper.class);
        exW.ex.printStackTrace();
    }
}

@JsonIgnoreProperties("stackTrace")
abstract class ExceptionMixIn extends Exception {

    @JsonCreator
    public ExceptionMixIn(@JsonProperty("message") String message) {
        super(message);
    }
}

@JsonIgnoreProperties("stackTrace")
abstract class ThrowableMixIn extends Throwable {

    @JsonCreator
    public ThrowableMixIn(@JsonProperty("message") String message) {
        super(message);
    }
}

class ExWrapper {

    public Exception ex;

    @Override
    public String toString() {
        return "ExWrapper{" +
                "ex=" + ex +
                '}';
    }
}

上面有原因的JSON的上面代码打印：

java.lang.Exception: Opps
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
    at com.fasterxml.jackson.databind.introspect.AnnotatedConstructor.call(AnnotatedConstructor.java:124)
    at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromObjectWith(StdValueInstantiator.java:283)
    at com.fasterxml.jackson.databind.deser.ValueInstantiator.createFromObjectWith(ValueInstantiator.java:229)
    at com.fasterxml.jackson.databind.deser.impl.PropertyBasedCreator.build(PropertyBasedCreator.java:195)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeUsingPropertyBased(BeanDeserializer.java:422)
    at com.fasterxml.jackson.databind.deser.std.ThrowableDeserializer.deserializeFromObject(ThrowableDeserializer.java:65)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159)
    at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:138)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:288)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:151)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4013)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2902)
Caused by: java.lang.Throwable: Root oops
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:422)
    at com.fasterxml.jackson.databind.introspect.AnnotatedConstructor.call(AnnotatedConstructor.java:124)
    at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromObjectWith(StdValueInstantiator.java:283)
    at com.fasterxml.jackson.databind.deser.ValueInstantiator.createFromObjectWith(ValueInstantiator.java:229)
    at com.fasterxml.jackson.databind.deser.impl.PropertyBasedCreator.build(PropertyBasedCreator.java:195)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeUsingPropertyBased(BeanDeserializer.java:422)
    at com.fasterxml.jackson.databind.deser.std.ThrowableDeserializer.deserializeFromObject(ThrowableDeserializer.java:65)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:159)
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:530)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeWithErrorWrapping(BeanDeserializer.java:528)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeUsingPropertyBased(BeanDeserializer.java:449)
    ... 8 more

您可以看到，异常具有默认的stackTrace，并且跳过了stackTrace有效负载中的JSON。

版本1

我没有进行过多的研究，但是启用allowSetters解决了这个问题：

@JsonIgnoreProperties(value = {"stackTrace"}, allowSetters = true)
public Exception ex;

您的带有此更改的代码将打印：

{"ex":{"cause":null,"message":"Oops","localizedMessage":"Oops","suppressed":[]}}
ExWrapper{ex=java.lang.Exception: Oops}