Question

我正在尝试创建一个java.lang.Exception存储为字段的类。另外，我正在尝试使用@JsonIgnoreProperties批注从堆栈化/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)

好吧，getMessage类中只有setMessage且没有Throwable，因此，除非您尝试删除@JsonIgnoreProperties批注，否则这似乎有点合理。它的工作原理很像是一种魅力：它可以正确地序列化和反序列化，而message的丢失setter突然不是问题。将"message"添加到忽略的字段也可以使其正常工作（但没有异常消息）。

我尝试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，而在存在注释时不会调用它们。 ThrowableDeserializer似乎有一些针对异常消息的技巧。我的猜测是，ThrowableDeserializer在缺少堆栈跟踪并且Jackson退回到默认Java Bean序列化程序时不可行。

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，所以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 +
                '}';
    }
}

JSON的上面的代码会打印出带有原因的异常：

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

如您所见，异常具有默认值stackTrace，并且stackTrace有效负载中的JSON被跳过。

版本1

我并没有进行过多研究，但是启用allowSetters可以解决此问题：

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

具有此更改的代码将打印：

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

使用Jackson序列化/反序列化异常而无需堆栈跟踪

1 个答案:

版本2

版本1