无法在Java中创建临时文件

Question

I have a Java method that takes byte array and String value as arguments and returns a File object. This is the code

public File createTempFile(byte[] byteArray, String fileName) throws IOException {
    String prefix = FilenameUtils.getBaseName(fileName);
    String suffix = getMimeType(byteArray);
    File tempFile = File.createTempFile(prefix, suffix, null);
    FileOutputStream fos = null;
    try {
        fos = new FileOutputStream(tempFile);
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
    fos.write(byteArray);
    fos.close();
    return tempFile;
}

When I try to run it like this

File myFile = tiedostoService.createTempFile(tiedosto.getContent(), attachment.getFileName());

I get an IOException like this

java.io.IOException: Unable to create temporary file, C:\Users\ROSHAN~1\AppData\Local\Temp\kuva1068864619970584773image\png
at java.io.File$TempDirectory.generateFile(File.java:1921)
at java.io.File.createTempFile(File.java:2010)

From the stacktrace. it can be seen that it's trying to create a file like C:\\Users\\ROSHAN~1\\AppData\\Local\\Temp\\kuva1068864619970584773image\\png and not C:\\Users\\ROSHAN~1\\AppData\\Local\\Temp\\kuva1068864619970584773image.png

How can I fix this? I'd really appreciate any sort of help.

Answer 1

'image/png' is a Mime Type. See all MimeTypes in java here

Write a util which converts mimetype to file extension. Hopefully this will help.

Answer 2

I think there is an extra \\ in your suffix string, could you try debug and see the actual value of the suffix?

I tried to run:

String suffix = "\\png";

and got the same error, but if I do

String suffix = ".png";

no error creating the temp file, notice that you need to add a dot in the suffix...