How to read a Multipart file as a string in Spring?

Question

I want to post a text file from my desktop using Advanced Rest Client. This is my controller:

@RequestMapping(value = "/vsp/debug/compareConfig/{deviceIp:.*}", method = RequestMethod.POST, consumes = { "multipart/form-data" }, produces = { "application/json" })

public ResponseEntity<SuccessResult> compareCLIs(HttpServletRequest request, @RequestParam("file") MultipartFile file, @PathVariable("deviceIp") String device) 
{
log.info(file.getOriginalFilename());
byte[] bytearr = file.getBytes();
log.info("byte length: ", bytearr.length);
log.info("Size : ", file.getSize());

}

This does not return any value for byte length or file size. I want to read the file values to a StringBuffer. Can someone provide pointers regarding this? I am not sure if I need to save this file before parsing it to a string. If so how do I save the file in the workspace?

You should avoid retrieving all the bytes at once. Instead, use MultiPartFile#getInputStream and use that stream to fill your StringBuilder (you don't need to use StringBuffer) or any other way to consume the data. — Luiggi Mendoza
– Luiggi Mendoza, Commented Jul 13, 2015 at 21:17

OlivierTerrien · Accepted Answer · 2020-03-28 01:02:57Z

53

If you want to load the content of a Multipart file into a String, the easiest solution is:

String content = new String(file.getBytes());

Or, if you want to specify the charset:

String content = new String(file.getBytes(), StandardCharsets.UTF_8);

However, if your file is huge, this solution is maybe not the best.

edited Mar 28, 2020 at 1:02

answered Apr 19, 2017 at 20:58

OlivierTerrien

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2 Comments

user12857969 Over a year ago

This is not working for me, doesn't return UTF characters.

Mrinal Bhattacharjee Over a year ago

Once the data is sent from the client, to my controller method. Is the entire file not loaded in memory at this point? Would reading the file at once cause problem then? @OlivierTerrien

Rodrigo Villalba Zayas · Accepted Answer · 2015-09-25 19:34:57Z

13

First, this is not related to Spring, and, second, you don't need to save the file to parse it.

To read the content of a Multipart file into a String you can use Apache Commons IOUtils class like this

ByteArrayInputStream stream = new   ByteArrayInputStream(file.getBytes());
String myString = IOUtils.toString(stream, "UTF-8");

edited Sep 25, 2015 at 19:34

answered Sep 25, 2015 at 15:07

Rodrigo Villalba Zayas

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1 Comment

Brent Bradburn Over a year ago

MultipartFile is a Spring type -- so the question is related to Spring. But once you call getBytes() you've entered the domain of generic Java.

UsamaAmjad · Accepted Answer · 2020-03-28 03:02:30Z

3

The given answers are correct but the top answer said it's not efficient for large files and the reason is that it keeps the whole file in memory which means if you are uploading a 2gb file it will consume that much of memory. Instead of doing that we can read the file line by line and Apache Commons IO provides a nice API for it.

LineIterator it = FileUtils.lineIterator(theFile, "UTF-8");
try {
    while (it.hasNext()) {
        String line = it.nextLine();
        // do something with line
    }
} finally {
    LineIterator.closeQuietly(it);
}

source

answered Mar 28, 2020 at 3:02

UsamaAmjad

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