java - Jackson ObjectMapper 即使使用 NON_NULL 也会抛出 NullPointerException

Question

当使用以下 JSON 并且“phones”或“emailAddresses”为空时，我将收到 NullPointerException。

JSON:

{
  "item": {
    "messages": {
      "user.phone.missing": {
        "type": "warning",
        "key": "user.phone.missing",
        "message": "User profile does not have a phone number",
        "code": null
      },
      "user.email.missing": {
        "type": "warning",
        "key": "user.email.missing",
        "message": "User profile does not have an email address",
        "code": null
      },
      "user.es.sync.failed": {
        "type": "error",
        "key": "user.es.sync.failed",
        "message": "Unable to sync user",
        "code": null
      }
    },
    "user": {
      "firstName": "Test",
      "middleInitial": null,
      "lastName": "User",
      "createdDt": "2016-04-20 19:50:03+0000",
      "updatedDt": null,
      "lastVerifiedDt": null,
      "status": "DEACTIVATED",
      "tokens": [
        {
          "tokenHash": "test hash",
          "tokenValue": "test dn",
          "createdDt": "2016-04-20 19:50:03+0000",
          "updatedDt": null,
          "status": "ENABLED"
        }
      ],
      "phones": null,
      "emailAddresses": null
    }
  },
  "status": "SUCCESS",
  "errors": []
}

这是堆栈跟踪:

Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: N/A (through reference chain: com.test.message.cte.CteItemResponse["item"]->com.test.message.cte.CteUserContext["user"]->com.test.User["phones"])
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty._throwAsIOE(SettableBeanProperty.java:510)
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty._throwAsIOE(SettableBeanProperty.java:493)
    at com.fasterxml.jackson.databind.deser.impl.MethodProperty.set(MethodProperty.java:116)
    at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:98)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:295)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121)
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:464)
    at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:98)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:295)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121)
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:464)
    at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:98)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:295)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:121)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2888)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2041)
    at com.test.Test.main(Test.java:20)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)
Caused by: java.lang.NullPointerException
    at com.test.User.setPhones(User.java:202)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.fasterxml.jackson.databind.deser.impl.MethodProperty.set(MethodProperty.java:114)
    ... 19 more

我正在像这样设置我的自定义 ObjectMapper:

package com.test;

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.util.ISO8601DateFormat;

public class MigrationObjectMapper extends ObjectMapper {
    private MigrationObjectMapper() {
        // do not serialize null value fields
        this.setSerializationInclusion(JsonInclude.Include.NON_NULL);

        configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
    }

    public static MigrationObjectMapper getMigrationObjectMapper(){
        return new MigrationObjectMapper();
    }
}

这意味着 CteUserContext cteUserContext = MigrationObjectMapper.getMigrationObjectMapper().convertValue(item.getItem(), new TypeReference<CteUserContext>(){});正在抛出错误。

CteUserContext内部是一个User对象，里面包含了List和List。难道这些不应该基于对象映射器配置进行序列化吗？

Answer 1

根据 Rocki 的评论:

setSerializationInclusion will ignore null values only for serialization not deserialization.

如果传入的“phones”值在我的 User 类中为空，我没有处理，所以它抛出了 NPE。我已经更新以确认它不为空。如果是，它将在任何其他逻辑之前短路:

/**
 * @param phones The phones
 */
@JsonProperty("phones")
public void setPhones(List<Phone> phones) {
    if ((phones != null) && (phones.size() > 1)) {
        int primaryIndex = -1;
        Phone primaryPhone = null;

        for (Phone p : phones) {
            if (p.getIsPrimary()) {
                primaryIndex = phones.indexOf(p);
                primaryPhone = p;
                break;
            }
        }

        phones.remove(primaryIndex);
        phones.add(0, primaryPhone);
    }
    this.phones = phones;
}