Return Zip File from ZipOutputStream in Java
Solution 1
You should be able to use a ByteArrayOutputStream
instead of a FileOutputStream
:
zipOutputStream = new ZipOutputStream(new ByteArrayOutputStream());
The difficulty here is to provide a File
to the method consuming the zip file. The java.io.File
does not provide an abstraction which allows you to manipulate in-memory files.
The java.io.File
abstraction and java.io.FileInputStream
implementation
To simplify, if we had to boil down what the File
abstraction is, we would see it as a URI
. And therefore, to be able to build an in-memory File
, or at least mimic it, we would need to provide an URI
which would then be used by the consumer of the File
to read its content.
If we look at the FileInputStream
which the consumer is likely to use, we can see that it always ends up with a native call which gives us to possibility whatsoever to abstract a FileSystem
for in-memory files:
// class java.io.FileInputStream
/**
* Opens the specified file for reading.
* @param name the name of the file
*/
private native void open0(String name) throws FileNotFoundException;
It would be easier if there was a possibility to adapt the consumer to accept an InputStream
, but from your problem statement I guess this is not possible.
API call
Your requirement is to provide a File
to the Watson Visual API.
Could you please provide the API method you need to call?
Solution 2
public void compressFileList(List<File> fileList, OutputStream outputStream)
throws IOException {
try (ZipOutputStream zipOutputStream =
new ZipOutputStream(new BufferedOutputStream(outputStream));
for (File file: fileList) {
try (FileInputStream fileInputStream = new FileInputStream(file)) {
ZipEntry zipEntry = new ZipEntry(file.getName());
zipOutputStream.putNextEntry(zipEntry);
byte[] tmp = new byte[4*1024];
int size = 0;
while((size = fileInputStream.read(tmp)) != -1){
zipOutputStream.write(tmp, 0, size);
}
zipOutputStream.flush();
} catch (FileNotFoundException e) { // Maybe skip not found files.
Logger.log(Level.INFO, "File not found {}", file.getPath());
}
}
}
}
Usage:
if (fileList.isEmpty()) {
...
return;
}
try {
compressFileList(fileList, servletRequest.getOutputStream())) {
} catch (FileNotFoundException e) {
...
} catch (IOException e) {
...
}
Vini
I started using SO in 2014 during my first development job in C#. Ever since I have been reading and learning a lot from SO. I am person with great hopes in Entrepreneurship but not forgetting the development skills that I have learned so far and still learning. I always am open to opportunities to meet people and learn new things. I always love the moment when I can think, "I would have never thought about it this way". Technology and people never cease to amaze me.
Updated on June 25, 2022Comments
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Vini almost 2 years
I have a function which creates a Zip file from a list of files. Is it possible to return the Zip file without it being saved on the disk? I need the file as I have to use the zip file as a parameter for another function. I am not sure of the ByteStream would be an option for me.
public File compressFileList(List<File> fileList,String fileName) { FileOutputStream fileOutputStream=null; ZipOutputStream zipOutputStream=null; FileInputStream fileInputStream=null; String compressedFileName=fileName +".zip"; if(fileList.isEmpty()) return null; try { fileOutputStream = new FileOutputStream(compressedFileName); zipOutputStream = new ZipOutputStream(new BufferedOutputStream(fileOutputStream)); for (File file: fileList) { fileInputStream = new FileInputStream(file); ZipEntry zipEntry = new ZipEntry(file.getName()); zipOutputStream.putNextEntry(zipEntry); byte[] tmp = new byte[4*1024]; int size = 0; while((size = fileInputStream.read(tmp)) != -1){ zipOutputStream.write(tmp, 0, size); } zipOutputStream.flush(); fileInputStream.close(); } zipOutputStream.close(); return compressedFile; //This is what I am missing } catch (FileNotFoundException e) { } catch (IOException e) { e.printStackTrace(); } return null; }
EDIT : adding the use case
The idea is to create a zip file and use the CreateClassifierOptions method of VisualRecognition Service of Watson.
classifierOptions = new CreateClassifierOptions.Builder() .classifierName("Santa") .addClass("Santa", new File("C:\\app\\GitRepo\\images\\beagle.zip")) .negativeExamples(new File("C:\\app\\GitRepo\\images\\nosport.zip")) .build();
The builder accepts the zip file as the parameter.
Understanding
Based on the explanation from Alexandre Dupriez, I think it is better to store the file at some place on the hard disk.
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Lino over 6 yearswhat does the other function accept as an Input? An
Inputstream
? -
Vini over 6 yearsI am using WatsonService API, which accepts a zip file as input. or maybe i should create a temp zip file and return it to the function
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Rob Obdeijn over 6 yearsYour question conflicts with your method signature. A File object is basically a reference to a file stored in some path, but your question seems to be about returning the (byte) contents of a file. So if you don't want to store your file somewhere, then you shouldn't be returning a File object.
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Vini over 6 yearsShould I create a temporary file on the disk and send it to function?
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Rob Obdeijn over 6 yearsWhat are you trying to achieve from a functional perspective? Storing a temporary file and returning a reference to it is an option, but it depends on what you want to do with that file.
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Vini over 6 yearsI want to use the Watson Visual API. The Visual API uses a zip file as argument. I have decided to store the file in a temporary folder and use it to call the Visual API.
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Vini over 6 yearsI have mentioned that I want the above function to return a File. The calling function accepts only a Zip file as input.
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Vini over 6 yearsIt doesnt return a file. I am looking for an option to return a zip file. I have reallized that i will have to save the file temporarily before I could use it for the next function.
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Alexandre Dupriez over 6 yearsYes, please - wonder what could be done and if there is a workaround
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Vini over 6 yearsI have added the use case. I assume that it is better to save the file and then call the watson service.
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Joop Eggen over 6 yearsOr (as int my answer) you can pass an OutputStream for delivery of the zip file. Then you do not need to maintain a byte array with the zip files content.