JavaでServerless Frameworkを使うときのリクエストとレスポンスには注意が必要 ref: https://qiita.com/jabaraster/items/f5805223d87a9f888774

file1.txt

{
  "httpMethod" : "POST",
  "requestContext" : {
    "httpMethod" : "POST",
    "accountId" : "*******",
    "apiId" : "*******",
    "resourceId" : "******",
    "identity" : {
      "userAgent" : "Apache-HttpClient\/4.5.x (Java\/1.8.0_112)",
      "userArn" : "arn:aws:iam::******:user\/****",
      "caller" : "***************",
      "cognitoAuthenticationProvider" : null,
      "cognitoIdentityId" : null,
      "accessKey" : "******************",
      "accountId" : "*****************",
      "sourceIp" : "test-invoke-source-ip",
      "apiKey" : "test-invoke-api-key",
      "cognitoAuthenticationType" : null,
      "cognitoIdentityPoolId" : null,
      "user" : "*******************"
    },
    "requestId" : "test-invoke-request",
    "stage" : "test-invoke-stage",
    "resourcePath" : "\/hello"
  },
  "resource" : "\/hello",
  "pathParameters" : null,
  "isBase64Encoded" : false,
  "headers" : null,
  "path" : "\/hello",
  "stageVariables" : null,
  "queryStringParameters" : null,
  "body" : "{\n    \"key1\": \"hoge\",\n    \"key2\": 120\n}"
}

Handler.java

package hello;

import java.io.IOException;

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;

public class Handler implements RequestHandler<Request, Response> {

    @Override
    public Response handleRequest(Request input, Context context) {
        return new Response("Go Serverless v1.0! Your function executed successfully!", input);
    }

}