Decompress a single file from a zip folder without writing in disk - scala

Question

Is it possible to decompress a single file from a zip folder and return the decompressed file without storing the data on the server?
I have a zip file with an unknown structure and I would like to develop a service that will serve the content of a given file on demand without decompressing the whole zip and also without writing on disk.
So, if I have a zip file like this
zip_folder.zip
| folder1
| file1.txt
| file2.png
| folder 2
| file3.jpg
| file4.pdf
| ...
So, I would like my service to receive the name and path of the file so I could send the file.
For example, fileName could be folder1/file1.txt
def getFileContent(fileName: String): IBinaryContent = {
val content: IBinaryContent = getBinaryContent(...)
val zipInputStream: ZipInputStream = new ZipInputStream(content.getInputStream)
val outputStream: FileOutputStream = new FileOutputStream(fileName)
var zipEntry: ZipEntry = null
var founded: Boolean = false
while ({
zipEntry = zipInputStream.getNextEntry
Option(zipEntry).isDefined && !founded
}) {
if (zipEntry.getName.equals(fileName)) {
val buffer: Array[Byte] = Array.ofDim(9000) // FIXME how to get the dimension of the array
var length = 0
while ({
length = zipInputStream.read(buffer)
length != -1
}) {
outputStream.write(buffer, 0, length)
}
outputStream.close()
founded = true
}
}
zipInputStream.close()
outputStream /* how can I return the value? */
}
How can I do it without writing the content in the disk?

Answer 1

You can use a ByteArrayOutputStream instead of the FileOutputStream to uncompress the zip entry into memory. Then call toByteArray() on it.
Also note that, technically, you would not even need to decompress the zip part if you can transmit it over a protocol (think: HTTP(S)) which supports the deflate encoding for its transport (which is usually the standard compression used in Zip files).

Answer 2

So, basically I did the same thing that #cbley recommended. I returned an array of bytes and defined the content-type so that the browser can do the magic!
def getFileContent(fileName: String): IBinaryContent = {
val content: IBinaryContent = getBinaryContent(...)
val zipInputStream: ZipInputStream = new ZipInputStream(content.getInputStream)
val outputStream: ByteArrayOutputStream = new ByteArrayOutputStream()
var zipEntry: ZipEntry = null
var founded: Boolean = false
while ({
zipEntry = zipInputStream.getNextEntry
Option(zipEntry).isDefined && !founded
}) {
if (zipEntry.getName.equals(fileName)) {
val buffer: Array[Byte] = Array.ofDim(zipEntry.getSize)
var length = 0
while ({
length = zipInputStream.read(buffer)
length != -1
}) {
outputStream.write(buffer, 0, length)
}
outputStream.close()
founded = true
}
}
zipInputStream.close()
outputStream.toByteArray
}
// in my rest service
#GET
#Path("/content/${fileName}")
def content(#PathVariable fileName): Response = {
val content = getFileContent(fileName)
Response.ok(content)
.header("Content-type", new Tika().detect(fileName)) // I'm using Tika but it's possible to use other libraries
.build()
}