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Asked: 2026-05-29T10:53:25+00:00

I want to use scala to parse a .mht file, but I found my

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I want to use scala to parse a .mht file, but I found my code is exactly like Java.

Following is a mht file sample:

From: <Save by Tencent MsgMgr>
Subject: Tencent IM Message
MIME-Version: 1.0
Content-Type:multipart/related;
    charset="utf-8"
    type="text/html";
    boundary="----=_NextPart_20CAFF23_6090_43fc_8C0A.EE179EE81D19"

------=_NextPart_20CAFF23_6090_43fc_8C0A.EE179EE81D19
Content-Type: text/html
Content-Transfer-Encoding:7bit

<html xmlns="http://www.w3.org/1999/xhtml"><head></head>...</html>

------=_NextPart_20CAFF23_6090_43fc_8C0A.EE179EE81D19
Content-Type:image/jpeg
Content-Transfer-Encoding:base64
Content-Location:{64172C34-99E7-40f6-A933-3DDCF670ACBA}.dat

/9j/4AAQSkZJRgABAQEAYABgAAD/2wBDAAMCAgMCAgMDAwMEAwMEBQgFBQQEBQoHBwYIDAoMDAsKCwsNDhIQDQ4RDgsLEBYQERMU
FRUVDA8XGBYUGBIUFRT/2wBDAQMEBAUEBQkFBQkUDQsNFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQU
FBQUFBQUFBT/wAARCAJwA7sDASIAAhEBAxEB/8QAHwAAAQUBAQEBAQEAAAAAAAAAAAECAwQFBgcICQoL/8QAtRAAAgEDAwIEAwUF
BAQAAAF9AQIDAAQRBRIhMUEGE1FhByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3ODk6Q0RFRkdISUpTVFVW
V1hZWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uHi

------=_NextPart_20CAFF23_6090_43fc_8C0A.EE179EE81D19
Content-Type:image/jpeg
Content-Transfer-Encoding:base64
Content-Location:{64172C34-99E7-40f6-A933-3DDCF670ACBA}.dat

/9j/4AAQSkZJRgABAQEAYABgAAD/2wBDAAMCAgMCAgMDAwMEAwMEBQgFBQQEBQoHBwYIDAoMDAsKCwsNDhIQDQ4RDgsLEBYQERMU
FRUVDA8XGBYUGBIUFRT/2wBDAQMEBAUEBQkFBQkUDQsNFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQU
FBQUFBQUFBT/wAARCAJwA7sDASIAAhEBAxEB/8QAHwAAAQUBAQEBAQEAAAAAAAAAAAECAwQFBgcICQoL/8QAtRAAAgEDAwIEAwUF
BAQAAAF9AQIDAAQRBRIhMUEGE1FhByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3ODk6Q0RFRkdISUpTVFVW
V1hZWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uHi

------=_NextPart_20CAFF23_6090_43fc_8C0A.EE179EE81D19
Content-Type:image/jpeg
Content-Transfer-Encoding:base64
Content-Location:{64172C34-99E7-40f6-A933-3DDCF670ACBA}.dat

/9j/4AAQSkZJRgABAQEAYABgAAD/2wBDAAMCAgMCAgMDAwMEAwMEBQgFBQQEBQoHBwYIDAoMDAsKCwsNDhIQDQ4RDgsLEBYQERMU
FRUVDA8XGBYUGBIUFRT/2wBDAQMEBAUEBQkFBQkUDQsNFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQUFBQU
FBQUFBQUFBT/wAARCAJwA7sDASIAAhEBAxEB/8QAHwAAAQUBAQEBAQEAAAAAAAAAAAECAwQFBgcICQoL/8QAtRAAAgEDAwIEAwUF
BAQAAAF9AQIDAAQRBRIhMUEGE1FhByJxFDKBkaEII0KxwRVS0fAkM2JyggkKFhcYGRolJicoKSo0NTY3ODk6Q0RFRkdISUpTVFVW
V1hZWmNkZWZnaGlqc3R1dnd4eXqDhIWGh4iJipKTlJWWl5iZmqKjpKWmp6ipqrKztLW2t7i5usLDxMXGx8jJytLT1NXW19jZ2uHi

------=_NextPart_20CAFF23_6090_43fc_8C0A.EE179EE81D19

There is a special line called boundary, which is a separator line:

------=_NextPart_20CAFF23_6090_43fc_8C0A.EE179EE81D19

The first part is some information about this file, which can be ignored. Following are 4 blocks, the first one is a html file, others are jpg images with base64 encoded text.

If I use Java, the code is like:

BufferedReader reader = new BufferedReader(new FileInputStream(new File("test.mht")))
String line = null;

String boundary = null;

// for a block
String contentType = null;
String encoding = null;
String location = null;
List<String> data = null;

while((line=reader.readLine())!=null) {
    // first, get the boundary
    if(boundary==null) {
        if(line.trim().startsWith("boundary=\"") {
             boundary = substringBetween(line, "\"", "\"");
        }
        continue;
    }

    if(line.equals("--"+boundary) { // new block
        if(contentType!=null) {
           // save data to a file
        }
        encoding=null;
        contentType=null;
        location = null;
        data = new ArrayList<String>();
    } else {
        if(id==null || contentType==null || location ==null) {
            if(line.trim().startsWith("Content-Type:") { /* get content type */ }
            // else check encoding
            // else check location
        } else {
            data.add(line);
        }
    }
}

I tried to use scala to rewrite the code, but I found the structure of my code is nearly the same, except I used the scala syntax instead of Java.

Is there a scala way to do the same work?

PS: I don’t want to load the full file into memory, since the file is huge. Instead I want to read and parse it line by line.

Thanks for helping!

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1 Answer

  1. Editorial Team

    This could be a very simple use case of state machine.

    import collection.mutable.ListBuffer
case class Part(contentType:Option[String], encoding:Option[String], location:Option[String], data:ListBuffer[String])

var boundary: String = null 

val Boundary = """.*boundary="(.*)"""".r
var state = 0
val IN_PART = 1
val IN_DATA = 2

var _contentType:Option[String] = None
var _encoding:Option[String] = None
var _location:Option[String] = None
var _data = new ListBuffer[String]()

Source.fromFile("test.mht").getLines.foreach{
  case Boundary(b) => boundary = b
  case `boundary` => 
    _contentType = None
    _encoding = None
    _location = None
    _data = new ListBuffer[String]()    
    state = IN_PART
  case "" => state match {
    case IN_PART => state = IN_DATA
    case IN_DATA => 
        var currentPart = Part(_contentType, _encoding, _location, _data)
        /* deal with current Part as allData.last */
    case _ =>
  }
  case line => state match {
    case IN_DATA => _data.append(line)            
    case IN_PART => line.split(":") match {
      case Array("Content-Type", t) => _contentType = Some(t)
      case Array("Content-Transfer-Encoding", e) => _encoding = Some(e)
      case Array("Content-Location", l) => _location = Some(l)
      case _ =>
    }
  }
}
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