Question

我想要投射的对象看起来像

public class AdDimension {
    private int width;
    private int height;

    public AdDimension() {
        // needed by Jackson
    }

    public AdDimension(final int width, final int height) {
        this.width = width;
        this.height = height;
    }
..
}

并在

中使用

public class Campaign {
    private String id;
    private List<AdDimension> adDimensions;

    public Campaign() {
        // needed by Jackson
    }
 ...
}

我尝试在测试中反序列化

@Test
public void testLoadCampaigns() throws IOException {
    final File campaignsFile = new File(getClass().getClassLoader().getResource("campaigns.json").getFile());
    final List<Campaign> campaigns = new JsonReader().loadCampaigns(campaignsFile);
    System.out.println(campaigns);
}

我的广告系列文件看起来像

[
  {
    "id": 1,
    "targetedCountries": ["CA", "IT"],
    "targetedDomain": "apple.com",
    "adDimensions": [[300,250], [600,200]]
  }
]

当我进行测试时，我看到了

com.fasterxml.jackson.databind.JsonMappingException: Can not deserialize instance of com.org.site.messages.AdDimension out of START_ARRAY token
 at [Source: /Users/harit/IdeaProjects/site/target/test-classes/campaigns.json; line: 6, column: 22] (through reference chain: java.util.ArrayList[0]->com.org.scout.messages.Campaign["adDimensions"]->java.util.ArrayList[0])
    at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:148)
    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:857)
    at com.fasterxml.jackson.databind.DeserializationContext.mappingException(DeserializationContext.java:853)
    at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromArray(BeanDeserializerBase.java:1257)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:157)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:136)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:245)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:217)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:25)
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:520)
    at com.fasterxml.jackson.databind.deser.impl.FieldProperty.deserializeAndSet(FieldProperty.java:101)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:258)
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:125)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:245)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:217)
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:25)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:3736)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2639)
    at com.org.harness.JsonReader.loadCampaigns(JsonReader.java:15)
    at com.org.harness.JsonReaderTest.testLoadCampaigns(JsonReaderTest.java:17)
    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:497)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
    at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:252)
    at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:141)
    at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:112)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.apache.maven.surefire.util.ReflectionUtils.invokeMethodWithArray(ReflectionUtils.java:189)
    at org.apache.maven.surefire.booter.ProviderFactory$ProviderProxy.invoke(ProviderFactory.java:165)
    at org.apache.maven.surefire.booter.ProviderFactory.invokeProvider(ProviderFactory.java:85)
    at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:115)
    at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:75)


Results :

Tests in error: 
  testLoadCampaigns(com.org.harness.JsonReaderTest): Can not deserialize instance of com.org.site.messages.AdDimension out of START_ARRAY token(..)

如何将[[300,250], [600,200]]读入List<AdDimension>？

Answer 1

默认情况下，Jackson会尝试将JSON数组值反序列化为Java数组类型或Collection类型（例如ArrayList）。但是您试图将[600,200]之类的JSON数组反序列化为AdDimension对象。这不会开箱即用。

您可以像建议的其他答案一样更改您的JSON，或者使用自定义反序列化策略。

您的第一个选择是定义自定义JsonDeserializer（尽管您应该使用其sublcass StdDeserializer）

class AdDimensionDeserializer extends JsonDeserializer<AdDimension> {
    @Override
    public AdDimension deserialize(JsonParser parser, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        // you have complete control over the tokens in the JSON, so validate as you wish
        ArrayNode arrayNode = parser.readValueAsTree();
        return new AdDimension(arrayNode.get(0).asInt(), arrayNode.get(1).asInt());
    }
}

并将其注册为

@JsonDeserialize(using = AdDimensionDeserializer.class)
class AdDimension {

Jackson将实例化AdDimensionDeserializer并使用该实例将JSON数组元素反序列化为AdDimension的实例。

另一种选择是使用@JsonCreater

标记注释，可用于定义构造函数和工厂方法作为一个用于实例化新实例的方法相关课程。

例如

@JsonCreator
public AdDimension(int[] dimensions) {
    // again, validate as required
    this.width = dimensions[0];
    this.height = dimensions[1];
}

杰克逊会找到这个构造函数并用它来反序列化你的JSON。它首先会尝试将文本[300,250]反序列化为int[]，它显然可以，然后将其传递给您的构造函数。

Answer 2

也许是一个糟糕的json格式？

我认为应该是这样的

[
  {
    "id": 1,
    "targetedCountries": ["CA", "IT"],
    "targetedDomain": "apple.com",
    "adDimensions": [{"width":300, "height":250}, {"width":600, "height":200}]
  }
]

我现在无法测试，但似乎不行。

如何将数组反序列化为对象？

2 个答案: