java - DynamoDB JsonMarshaller 无法反序列化对象列表

Question

我有一个 Java 类，它是 DynamoDB 中表的数据模型。我想使用 DynamoDBMapper至 save和 load来自 Dynamo 的元素。该类的一名成员是List<MyObject> .所以我用了 JsonMarshaller<List<MyObject>>序列化和反序列化该字段。

列表可以通过 JsonMarshaller 成功序列化.但是，当我尝试取回条目并读取列表时，它会抛出异常:java.lang.ClassCastException: java.util.LinkedHashMap cannot be cast to MyObject .看起来像 JsonMarshaller将数据反序列化为 LinkedHashMap而不是 MyObject .我怎样才能摆脱这个问题？

MCVE:

// Model.java
@DynamoDBTable(tableName = "...")
public class Model {
  private String id;
  private List<MyObject> objects;

  public Model(String id, List<MyObject> objects) {
    this.id = id;
    this.objects = objects;
  }

  @DynamoDBHashKey(attributeName = "id")
  public String getId() { return this.id; }
  public void setId(String id) { this.id = id; }

  @DynamoDBMarshalling(marshallerClass = ObjectListMarshaller.class)
  public List<MyObject> getObjects() { return this.objects; }
  public void setObjects(List<MyObject> objects) { this.objects = objects; }
}

---

// MyObject.java
public class MyObject {
  private String name;
  private String property;

  public MyObject() { }
  public MyObject(String name, String property) {
    this.name = name;
    this.property = property;
  }

  public String getName() { return this.name; }
  public void setName(String name) { this.name = name; }

  public String getProperty() { return this.property; }
  public void setProperty(String property) { this.property = property; }
}

---

// ObjectListMarshaller.java
public class ObjectListMarshaller extends JsonMarshaller<List<MyObject>> {}

---

// Test.java
public class Test {
  private static DynamoDBMapper mapper;

  static {
    AmazonDynamoDBClient client = new AmazonDynamoDBClient(new ProfileCredentialsProvider()
    mapper = new DynamoDBMapper(client);
  }

  public static void main(String[] args) {
    MyObject obj1 = new MyObject("name1", "property1");
    MyObject obj2 = new MyObject("name2", "property2");
    List<MyObject> objs = Arrays.asList(obj1, obj2);

    Model model = new Model("id1", objs);
    mapper.save(model); // success

    Model retrieved = mapper.load(Model.class, "id1");
    for (MyObject obj : retrieved.getObjects()) { // exception
    }
  }
}

Answer 1

在较新的版本中，只需使用:

@DynamoDBAttribute(attributeName = "things")
public List<Thing> getThings() {
    return things;
}

public void setThings(final List<Thing> things) {
    this.things = things;
}

鉴于 Thing 被注释为:

@DynamoDBDocument
public class Thing {
}