java - Jackson 与 Kotlin : how to serialize only annotated properties

Question

我正在尝试在现有的 Java 项目中开始使用 Kotlin，但 Jackson 没有检测到我的 Kotlin 对象中的 @JsonProperty(尽管它与 Java 对象完美配合)。

有什么方法可以配置 Jackson，使其适用于 Kotlin，就像它适用于 Java 一样？

这是 Java 类:

public class TestJavaObj {
    @JsonProperty
    private String includeMe;
    private String dontIncludeMe;

    public TestJavaObj(String includeMe, String dontIncludeMe) {
        this.includeMe = includeMe;
        this.dontIncludeMe = dontIncludeMe;
    }
}

和 Kotlin 类:

class TestKotlinObj(
    @JsonProperty val includeMe: String,
    val dontIncludeMe : String?
)

这是测试代码:

public static void main(String[] args) throws JsonProcessingException {
    ObjectMapper mapper = new ObjectMapper()
            .registerModule(new KotlinModule()) //jackson-module-kotlin
            .configure(MapperFeature.AUTO_DETECT_GETTERS, false)
            .configure(MapperFeature.AUTO_DETECT_CREATORS, false)
            .configure(MapperFeature.AUTO_DETECT_FIELDS, false)
            .configure(MapperFeature.AUTO_DETECT_IS_GETTERS, false)
            .configure(MapperFeature.AUTO_DETECT_SETTERS, false);

    TestJavaObj javaObj = new TestJavaObj("hello", "world");
    TestKotlinObj kotlinObj = new TestKotlinObj("hello", "world");

    System.out.println("Expected: " + mapper.writeValueAsString(javaObj));
    System.out.println("Got: " + mapper.writeValueAsString(kotlinObj));
}

这是输出:

Expected: {"includeMe":"hello"}
Got: {}

我的 gradle 文件中的版本号:

kotlin_version = '1.3.72'
...
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
classpath "org.jetbrains.kotlin:kotlin-allopen:$kotlin_version" 
...
apply plugin: 'kotlin'
...
compile('com.fasterxml.jackson.core:jackson-annotations:2.10.3')
compile('com.fasterxml.jackson.module:jackson-module-kotlin:2.9.8')
compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"

Answer 1

指定注释use-site target :

class TestKotlinObj(
        @get:JsonProperty val includeMe: String,
        val dontIncludeMe : String
)

结果:

Expected: {"includeMe":"hello"}
Got: {"includeMe":"hello"}

---

背景:

翻译成Java字节码的类只有一个构造函数参数注释:

public final class TestKotlinObj {
   @NotNull // no annotation here
   private final String includeMe;
   @NotNull
   private final String dontIncludeMe;

   @NotNull // nor here
   public final String getIncludeMe() {
      return this.includeMe;
   }

   @NotNull
   public final String getDontIncludeMe() {
      return this.dontIncludeMe;
   }
                     // but here
                     // vvvv 
   public TestKotlinObj(@JsonProperty @NotNull String includeMe, @NotNull String dontIncludeMe) {
      Intrinsics.checkParameterIsNotNull(includeMe, "includeMe");
      Intrinsics.checkParameterIsNotNull(dontIncludeMe, "dontIncludeMe");
      super();
      this.includeMe = includeMe;
      this.dontIncludeMe = dontIncludeMe;
   }
}

序列化对象时不会考虑这一点。

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