使用AWS SDK调用Lambda Function URL时触发NullPointerException

我正尝试在Java应用中通过Function URL调用AWS Lambda函数，使用Java AWS SDK 2.18.7对请求进行签名，但始终无法成功。我拥有具备Lambda Function URL执行权限的用户的访问密钥和秘密密钥。

代码在第150行Response awsResponse = reb.execute();处崩溃，代码如下：

Request<Void> request = new DefaultRequest<Void>("lambda");
request.setHttpMethod(HttpMethodName.POST);
request.setEndpoint(URI.create(this.LAMBDA_URL));
request.setContent(new ByteArrayInputStream(postJsonString.getBytes(StandardCharsets.UTF_8)));
Map<String, String> headers = new HashMap<String, String>();
headers.put("Content-Length", Integer.toString(postJsonString.length()));
request.setHeaders(headers);
// Sign AWS Request
AWS4Signer signer = new AWS4Signer();
signer.setRegionName(MY_REGION);
signer.setServiceName(request.getServiceName());
BasicAWSCredentials awsCreds = new BasicAWSCredentials(ACCESS_KEY, SECRET_KEY);
signer.sign(request, awsCreds);
// Execute and get response
ClientConfiguration config = new ClientConfiguration();
AmazonHttpClient client = new AmazonHttpClient(config);
RequestExecutionBuilder reb = client.requestExecutionBuilder();
reb = reb.request(request);
reb = reb.executionContext(new ExecutionContext());
Response<Void> awsResponse = reb.execute();

控制台输出的异常信息：

Exception in thread "main" java.lang.NullPointerException
    at com.amazonaws.http.AmazonHttpClient$RequestExecutor.handleErrorResponse(AmazonHttpClient.java:1879)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutor.handleServiceErrorResponse(AmazonHttpClient.java:1418)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutor.executeOneRequest(AmazonHttpClient.java:1387)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutor.executeHelper(AmazonHttpClient.java:1157)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutor.doExecute(AmazonHttpClient.java:814)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutor.executeWithTimer(AmazonHttpClient.java:781)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutor.execute(AmazonHttpClient.java:755)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutor.access$500(AmazonHttpClient.java:715)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutionBuilderImpl.execute(AmazonHttpClient.java:697)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutionBuilderImpl.execute(AmazonHttpClient.java:702)
    at aws_auth_awssdk2_18_7.Main.aws_sdk_attemp(Main.java:150)
    at aws_auth_awssdk2_18_7.Main.main(Main.java:67)

问题根源与修复方案 #

1. SDK版本混淆
   你使用的是AWS SDK v2的版本号，但代码全是v1的API（DefaultRequest、AWS4Signer、AmazonHttpClient等），v1和v2的API完全不兼容，这是核心问题。必须统一使用v2的规范实现。

2. 缺失必要请求头
   Lambda Function URL要求请求携带Content-Type: application/json头，你当前代码未设置，会导致请求被拒绝，进而触发错误响应处理时的空指针异常。

3. 修正后的v2代码示例

import software.amazon.awssdk.auth.credentials.AwsBasicCredentials;
import software.amazon.awssdk.auth.signer.Aws4Signer;
import software.amazon.awssdk.core.SdkBytes;
import software.amazon.awssdk.http.SdkHttpFullRequest;
import software.amazon.awssdk.http.SdkHttpMethod;
import software.amazon.awssdk.http.urlconnection.UrlConnectionHttpClient;
import software.amazon.awssdk.regions.Region;

import java.io.InputStream;
import java.net.URI;
import java.util.HashMap;
import java.util.Map;

public class LambdaUrlCaller {
    private static final String LAMBDA_URL = "你的Function URL";
    private static final String ACCESS_KEY = "你的访问密钥";
    private static final String SECRET_KEY = "你的秘密密钥";
    private static final Region REGION = Region.of("你的区域");

    public static void main(String[] args) {
        String postJson = "{\"test\": \"data\"}";

        // 构建请求头
        Map<String, String> headers = new HashMap<>();
        headers.put("Content-Type", "application/json");

        // 构建未签名请求
        SdkHttpFullRequest.Builder requestBuilder = SdkHttpFullRequest.builder()
                .method(SdkHttpMethod.POST)
                .uri(URI.create(LAMBDA_URL))
                .headers(headers)
                .contentStreamProvider(() -> SdkBytes.fromUtf8String(postJson).asInputStream());

        // 签名请求
        Aws4Signer signer = Aws4Signer.create();
        SdkHttpFullRequest signedRequest = signer.sign(
                requestBuilder.build(),
                Aws4Signer.builder()
                        .credentials(AwsBasicCredentials.create(ACCESS_KEY, SECRET_KEY))
                        .region(REGION)
                        .serviceName("lambda")
                        .build()
        );

        // 执行请求并处理响应
        try (UrlConnectionHttpClient client = UrlConnectionHttpClient.create()) {
            software.amazon.awssdk.http.HttpResponse response = client.execute(signedRequest);
            System.out.println("响应状态码: " + response.statusCode());
            
            // 读取响应内容
            InputStream responseStream = response.contentStreamProvider().get();
            // 处理响应流逻辑...
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

额外注意事项 #

• 确认Lambda Function URL的认证类型设置为AWS_IAM，否则签名会被忽略或拒绝。
• 确保IAM用户的权限策略包含lambda:InvokeFunctionUrl，并指定正确的Function ARN。
• v2 SDK会自动处理Content-Length，无需手动计算，避免编码不一致导致的长度错误。

内容的提问来源于stack exchange，提问作者benino