DynamoDBMapper - 无法实例化类

Question

我在亚马逊的AWS工具包中遇到了基于Java的DynamoDBMapper的问题,抛出了"未能实例化类"异常错误.这是我第一次尝试使用DBMapper,所以我不完全确定我的设置是否正确.我的代码可以在下面找到:

public static void main(String[] args) {
    dynamoDB = new AmazonDynamoDBClient(credentials);

    DynamoDBMapper mapper = new DynamoDBMapper(dynamoDB);
    PStatus data = mapper.load(PStatus.class, "online", new Integer(1655));
    String assigned = data.getAssigned();
    System.out.println(assigned);
}

@DynamoDBTable(tableName = "projectStatus")
public class PStatus {

    private Integer projID;
    private String status;
    private String assigned;

    @DynamoDBHashKey(attributeName = "status")
    public String getStatus() { return status; }
    public void setStatus(String status) { this.status = status; }

    @DynamoDBRangeKey(attributeName = "projID")
    public Integer getId() { return projID; }
    public void setId(Integer projID) { this.projID = projID; }

    @DynamoDBAttribute(attributeName = "assigned")
    public String getAssigned() { return assigned; }
    public void setAssigned(String assigned) { this.assigned = assigned; }
}

我基本上只是尝试执行GetItemRequest然后绘制一个特定的属性,但我得到指向该行的错误PStatus data = mapper.load(PStatus.class, "onFarm", new Integer(1655));.我究竟做错了什么？

编辑:下面的确切异常:

Exception in thread "main" com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMappingException: Failed to instantiate class
    at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.createKeyObject(DynamoDBMapper.java:325)
    at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.load(DynamoDBMapper.java:313)
    at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.load(DynamoDBMapper.java:212)
    at test.TestGet.main(TestGet.java:20)
Caused by: java.lang.InstantiationException: test.TestGet$PStatus
    at java.lang.Class.newInstance0(Unknown Source)
    at java.lang.Class.newInstance(Unknown Source)
    at com.amazonaws.services.dynamodbv2.datamodeling.DynamoDBMapper.createKeyObject(DynamoDBMapper.java:323)

Answer 1

添加空构造函数,以便调用java.lang.Class.newInstance0(未知源)将起作用:

public PStatus()
{

}

Answer 2

刚刚找到答案。这与我的想法不太一样，但最终我把课程放在了错误的位置。从他们展示的方式来看，我的印象是它是一个子类，但 PStatus 需要是它自己的类、文件等等。我试图在 TestGet 中对它进行子类化，但它不喜欢这样。我猜这更多是我遇到的 Java 问题，而不是 DBMapper 的问题。仍在学习！