如何从 DynamoDB 流新映像中获取纯 Json 字符串？

json java aws-sdk amazon-dynamodb-streams

2022-09-03 06:44:12

我有一个启用了流的 Dynamodb 表。此外，我还为此表创建了一个触发器，该触发器调用 AWS Lambda 函数。在此 lambda 函数中，我尝试从 Dynamodb 流中读取新图像（修改后的 Dynamodb 项），并尝试从中获取纯 json 字符串。我的问题是，如何获取通过流发送的 DynamoDB 项目的纯 json 字符串？我正在使用下面给出的代码片段来获取新的图像，但我不知道如何从中获取json字符串。感谢您的帮助。

public class LambdaFunctionHandler implements RequestHandler<DynamodbEvent, Object> {

@Override
public Object handleRequest(DynamodbEvent input, Context context) {
    context.getLogger().log("Input: " + input);

    for (DynamodbStreamRecord record : input.getRecords()){

        context.getLogger().log(record.getEventID());
        context.getLogger().log(record.getEventName());
        context.getLogger().log(record.getDynamodb().toString());
        Map<String,AttributeValue> currentRecord = record.getDynamodb().getNewImage();

        //how to get the pure json string of the new image
        //..............................................
     }
     return "Successfully processed " + input.getRecords().size() + " records.";
}

}

答案 1

以下是从 Dynamo JSON 转换为标准 JSON 的完整代码：

import com.amazonaws.services.dynamodbv2.document.Item;
import com.amazonaws.services.dynamodbv2.document.internal.InternalUtils;
import com.amazonaws.services.dynamodbv2.model.AttributeValue;
import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;
import com.amazonaws.services.lambda.runtime.events.DynamodbEvent;
import com.amazonaws.services.lambda.runtime.events.DynamodbEvent.DynamodbStreamRecord;
import com.google.gson.Gson;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

/**
 * Main Lambda class to receive event stream, parse it to Survey
 * and process them.
 */
public class SurveyEventProcessor implements
        RequestHandler<DynamodbEvent, String> {

    private static final String INSERT = "INSERT";

    private static final String MODIFY = "MODIFY";

    public String handleRequest(DynamodbEvent ddbEvent, Context context) {

        List<Item> listOfItem = new ArrayList<>();
        List<Map<String, AttributeValue>> listOfMaps = null;
        for (DynamodbStreamRecord record : ddbEvent.getRecords()) {

            if (INSERT.equals(record.getEventName()) || MODIFY.equals(record.getEventName())) {
                listOfMaps = new ArrayList<Map<String, AttributeValue>>();
                listOfMaps.add(record.getDynamodb().getNewImage());
                listOfItem = InternalUtils.toItemList(listOfMaps);
            }

            System.out.println(listOfItem);
            try {
               // String json = new ObjectMapper().writeValueAsString(listOfItem.get(0));
                Gson gson = new Gson();
                Item item = listOfItem.get(0);

                String json = gson.toJson(item.asMap());
                System.out.println("JSON is ");
                System.out.println(json);
            }catch (Exception e){
                e.printStackTrace();
            }
        }


        return "Successfully processed " + ddbEvent.getRecords().size() + " records.";
    }
}

答案 2

在 c# 中，您可以使用 DynamoDB 文档类将 newImage 转换为纯 json

使用 Amazon.DynamoDBv2.DocumentModel;

var streamRecord = dynamoEvent.Records.First（）;

var jsonResult=Document.FromAttributeMap（streamRecord.Dynamodb.NewImage）.Tojson（）;

如果你想进一步将json转换为对象，你可以使用Newtonsoft。

使用 Newtonsoft.Json;

TModel model = JsonConvert.DeserializeObject（jsonResult）;