AWS Lambda中java.io.FileNotFoundException(只读文件系统)问题咨询

问题1：Lambda只读文件系统导致写入失败 #

原代码 #

file = new File(fileName);// fileName is just a String.txt
context.getLogger().log("File Path1: "+file.getAbsolutePath());
FileUtils.writeLines(file, failedMessages); //failedMessages is a List<String>
context.getLogger().log("File Path2: "+file.getAbsolutePath());

错误日志 #

File Path1: /var/task/Platform_Status_Failed_2022_09_09.txt

Exception caught java.io.FileNotFoundException: Platform_Status_Failed_2022_09_09.txt (Read-only file system)

修复方案 #

AWS Lambda的/var/task目录是只读的，仅/tmp目录支持文件写入。必须将文件路径改为/tmp/前缀：

String tmpFilePath = "/tmp/" + fileName;
File file = new File(tmpFilePath);
context.getLogger().log("File Path1: "+file.getAbsolutePath());
FileUtils.writeLines(file, failedMessages);
context.getLogger().log("File Path2: "+file.getAbsolutePath());

问题2：使用/tmp后上传S3找不到文件的异常 #

错误日志 #

Unable to calculate MD5 hash: /tmp/Platform_Status_Failed_2022_09_09.txt (No such file or directory): java.lang.BootstrapMethodError
java.lang.BootstrapMethodError: Unable to calculate MD5 hash: /tmp/Platform_Status_Failed_2022_09_09.txt (No such file or directory)
    at com.paytmmoney.bo.equities.lambda.handler.LambdaMethodHandler.uploadToS3(LambdaMethodHandler.java:171)
    at com.paytmmoney.bo.equities.lambda.handler.LambdaMethodHandler.uploadFileToS3(LambdaMethodHandler.java:88)
    at com.paytmmoney.bo.equities.lambda.handler.LambdaMethodHandler.handleRequest(LambdaMethodHandler.java:58)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
Caused by: com.amazonaws.SdkClientException: Unable to calculate MD5 hash: /tmp/Platform_Status_Failed_2022_09_09.txt (No such file or directory)
    at com.amazonaws.services.s3.AmazonS3Client.getInputStream(AmazonS3Client.java:1849)
    at com.amazonaws.services.s3.AmazonS3Client.uploadObject(AmazonS3Client.java:1767)
    at com.amazonaws.services.s3.AmazonS3Client.putObject(AmazonS3Client.java:1746)
    at com.paytmmoney.bo.equities.lambda.handler.LambdaMethodHandler.uploadToS3(LambdaMethodHandler.java:159)
    ... 6 more
Caused by: java.io.FileNotFoundException: /tmp/Platform_Status_Failed_2022_09_09.txt (No such file or directory)
    at java.io.FileInputStream.open0(Native Method)
    at java.io.FileInputStream.open(FileInputStream.java:195)
    at java.io.FileInputStream.<init>(FileInputStream.java:138)
    at com.amazonaws.util.Md5Utils.computeMD5Hash(Md5Utils.java:97)
    at com.amazonaws.util.Md5Utils.md5AsBase64(Md5Utils.java:104)
    at com.amazonaws.services.s3.AmazonS3Client.getInputStream(AmazonS3Client.java:1845)
    ... 9 more

可能原因及修复方案 #

1. 文件写入未完成或路径错误
   确保写入时使用完整绝对路径，并验证文件是否存在：

   String tmpFilePath = "/tmp/" + fileName;
   File file = new File(tmpFilePath);
   try {
       FileUtils.writeLines(file, failedMessages);
       // 写入后验证文件状态
       if (file.exists() && file.length() > 0) {
           context.getLogger().log("文件写入成功：" + tmpFilePath);
       } else {
           throw new RuntimeException("文件写入后为空或不存在");
       }
   } catch (IOException e) {
       context.getLogger().log("写入文件失败：" + e.getMessage());
       throw new RuntimeException("文件写入失败", e);
   }
   

2. 上传路径拼写错误
   确认S3上传代码中使用的路径与写入路径完全一致，不要遗漏/tmp/前缀或拼写错误。

3. 绕过文件写入，直接用内存流上传
   若无需持久化文件，建议直接通过内存流上传到S3，避免磁盘IO问题：

   import java.nio.charset.StandardCharsets;
   import java.io.ByteArrayInputStream;
   import com.amazonaws.services.s3.model.PutObjectRequest;
   import com.amazonaws.services.s3.model.ObjectMetadata;
   
   // 将List<String>转为字节流
   String content = String.join(System.lineSeparator(), failedMessages);
   byte[] contentBytes = content.getBytes(StandardCharsets.UTF_8);
   ByteArrayInputStream inputStream = new ByteArrayInputStream(contentBytes);
   
   // 上传到S3
   ObjectMetadata metadata = new ObjectMetadata();
   metadata.setContentLength(contentBytes.length);
   PutObjectRequest request = new PutObjectRequest("your-bucket-name", "s3-file-key", inputStream, metadata);
   amazonS3.putObject(request);
   

内容的提问来源于stack exchange，提问作者Aditya K