在JAVA中使用lambda AWS DynamoDB触发

本文介绍了在JAVA中使用lambda AWS DynamoDB触发的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我试图触发Java编写的AWS lambda表达式，在dynamodb流事件。亚马逊具有相同的指导，采用NodeJS这里 HTTP：//docs.aws.amazon .COM /λ/最新/ DG / WT-DDB创建，测试function.html

I am trying to trigger an AWS lambda function written in Java, on dynamodb stream events. Amazon has a guide for the same, using NodeJS here docs.aws.amazon/lambda/latest/dg/wt-ddb-create-test-function.html

测试输入NodeJS（从上面的链接）看起来像一个SNS的事件，所以我试图用相应的SNSEvent类在Java中，作为给我的处理方法。

The testing input for NodeJS (from the above link) looks like an SNS event, so I tried to use the corresponding SNSEvent class in Java as an input to my handler method.

import com.amazonaws.services.lambda.runtime.Context; import com.amazonaws.services.lambda.runtime.LambdaLogger; import com.amazonaws.services.lambda.runtime.events.SNSEvent; import com.amazonaws.services.lambda.runtime.events.SNSEvent.SNSRecord; import java.util.List; public class RecomFunction { public void handler(SNSEvent event, Context context) { LambdaLogger logger = context.getLogger(); List<SNSRecord> records = event.getRecords(); if (records != null) { for (SNSRecord record : records) { if (record != null) { logger.log("SNS record: " + record.getSNS().getMessage()); } } } } }

不幸的是，record.getSNS（）产生一个空指针异常返回NULL

Unfortunately, record.getSNS() returns NULL resulting to a NullPointer exception

有一个相关的问题，但一个明确的答案没有给出： 设置DynamoDB触发使用lambda

There is a related question, however a specific answer was not given: Setup DynamoDB Trigger using Lambda

推荐答案

这工作对我来说 - 案例DynamoDB流事件：

This worked for me - case DynamoDB stream events:

import com.amazonaws.services.lambda.runtime.RequestHandler; ... public class DynamoStreamHandler implements RequestHandler<Object, Void> { @Override public Void handleRequest(Object o, Context context) { LinkedHashMap lhm = (LinkedHashMap) o; ...etc. } }

看来他们使用自定义的JSON映射器，它利用地图和列表的对象。这是非常简单的（但繁琐），以验证这一点通过测试和打印郊游日志等事件类型。 （叹气）

It seems they use a customized JSON mapper which utilizes Map and List objects. It's quite straightforward (but tedious) to verify this for other event types by testing and print-outing logs. (sigh)

编辑：：如果〜5 MB的开销就可以了，你可以使用 DynamodbEvent.DynamodbStreamRecord 按提供的AWS-拉姆达-java-事件库中的 AWS LAMBDA演练3：处理亚马逊DynamoDB活动（爪哇）的在AWS LAMBDA文档

If ~5 MB overhead is ok, you can use DynamodbEvent.DynamodbStreamRecord provided by aws-lambda-java-events library as described in AWS Lambda Walkthrough 3: Process Amazon DynamoDB Events (Java) in AWS Lambda Documentation.