Send byte array and receive String through REST web service

Question

in my Spring Rest web service I send a file (even big size) as byte array but when I receive the information, the object is a String so when I make the cast from Object to byte[] I receive the following error:

java.lang.ClassCastException: java.lang.String cannot be cast to [B

The originl file is converted through

Files.readAllBytes(Paths.get(path))

and this byte[] is filled in one object with a field result of Object type. When the Client retrieve this object and it gets result class with cast to byte[] it appears the above exception, this is the client code

Files.write(Paths.get("test.txt"),((byte[])response.getResult()));

If I use a cast to string and then to bytes the content of the file is different from original file. I don't care the file type, file content, I only have to copy from server to client directory How can I do?Thanks

server class:

@Override
    @RequestMapping(value = "/", method = RequestMethod.GET)
    public @ResponseBody Response getAcquisition(@RequestParam(value="path", defaultValue="/home") String path){
        try {
            byte[] file = matlabClientServices.getFile(path);
            if (file!=null){
                FileTransfer fileTransfer= new FileTransfer(file, Paths.get(path).getFileName().toString());
                return new Response(true, true, fileTransfer, null);
            }
            else 
                return new Response(false, false, "File doesn't exist!", null);         
        } catch (Exception e) {
            ErrorResponse errorResponse= ErrorResponseBuilder.buildErrorResponse(e);
            LOG.error("Threw exception in MatlabClientControllerImpl::getAcquisition :" + errorResponse.getStacktrace());
            return new Response(false, false, "Error during file retrieving!", errorResponse);
        }       
    }

and FileTransfer is:

    public class FileTransfer {

        private byte[] content;
        private String name;
..get and set

client class:

    @RequestMapping(value = "/", method = RequestMethod.GET)
public @ResponseBody Response getFile(@RequestParam(value="path", defaultValue="/home") String path){
    RestTemplate restTemplate = new RestTemplate();
    Response response = restTemplate.getForObject("http://localhost:8086/ATS/client/file/?path={path}", Response.class, path);
    if (response.isStatus() && response.isSuccess()){
        try {
            @SuppressWarnings("unchecked")
            LinkedHashMap<String,String> result= (LinkedHashMap<String,String>)response.getResult();
            //byte[] parseBase64Binary = DatatypeConverter.parseBase64Binary((String)fileTransfer.getContent());
            Files.write(Paths.get(result.get("name")), DatatypeConverter.parseBase64Binary(result.get("content"))); 
            return new Response(true, true, "Your file has been written!", null);
            } catch (IOException e) {
            return new Response(true, true, "Error writing your file!!", null);
        }
    }
    return response;
}

Can you show how you defined the rest endpoint and such? What content type is it accepting? if it's json, then byte[] would be sent as Base64 encoded string. Given the right mapper you can get this as byte[]. — zapl
– zapl, Commented Nov 24, 2015 at 15:12
How does your Response class look like? It should not contain Object it should be a byte[] field. — zapl
– zapl, Commented Nov 24, 2015 at 15:40
it contains object because Response is used for all web service — luca
– luca, Commented Nov 24, 2015 at 15:59
I'd consider changing the response class if you don't actually have the same response all the time. "Q2lhbyBNb25kbw==" is otherwise just a string for the deserializer. If you tell it to deserialize e.g. a BinaryResponse class that has a byte[] field it would do the datatype conversion stuff for you. Response<GenericType> (not sure if that works thouhg) or sub classes — zapl
– zapl, Commented Nov 24, 2015 at 16:07

luca · Accepted Answer · 2015-11-24 16:09:48Z

2

So the client should be something like this

@RequestMapping(value = "/test/", method = RequestMethod.GET)
    public Response getFileTest(@RequestParam(value="path", defaultValue="/home") String path){
        RestTemplate restTemplate = new RestTemplate();
        Response response = restTemplate.getForObject("http://localhost:8086/ATS/client/file/?path={path}", Response.class, path);
        if (response.isStatus() && response.isSuccess()){
            try {
                byte[] parseBase64Binary = DatatypeConverter.parseBase64Binary((String)response.getResult());
                Files.write(Paths.get("test.txt"),parseBase64Binary );
            } catch (IOException e) {
            }
        }
        return response;
    }

edited Nov 24, 2015 at 16:09

luca

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answered Nov 24, 2015 at 15:48

awsome

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6 Comments

luca Over a year ago

it works, great. Is there a way to retrieve the file name and extension(otherwise I don't know the original file)? or I have tu use an object with name and file?

awsome Over a year ago

you have to use an object with name and file.. byte array is only the content of the file

luca Over a year ago

I update with new and working code, do you think it is correct? I had to use LinkedHashMap<String,String> instead of FileTrasfer because otherwise I received exception

awsome Over a year ago

what was the exception

luca Over a year ago

it is not possible cast LinkedHashMap in FileTrasfer, getForObject return Response object but with LinkedHashMap instead of FileTrasfer

|

mtyurt · Accepted Answer · 2015-11-24 15:28:43Z

0

I believe the content-type here is text/plain, therefore the content of the file is a plain text. Simply generate byte array from the response:

 Files.write(Paths.get("test.txt"),((String)response.getResult()).getBytes());

answered Nov 24, 2015 at 15:28

mtyurt

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3 Comments

luca Over a year ago

as I have written in the main post, if I cast to String and use getBytes I receive not "Hello world" but "Q2lhbyBNb25kbw==".

Joop Eggen Over a year ago

@luca which is Base64 for "Ciao Mondo" - see awsome.

asgs Over a year ago

might want to be explicit in specifying the Charset when it comes to encoding Strings to bytes.

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