How to extract a single file from a zip archive in MATLAB?

Question

Single File unzip

The unzip() function in MATLAB only provides the ability to input a zip file location and an output directory location. Is there a way to extract only one file from the zip archive instead of all the files?

If the specific file is known and it is the only file needed, this will reduce the amount of time to extract the file.

Answer 1

MATLAB's unzip

This is not possible with the standard MATLAB function, however...lets hack the function to make it do what is needed!

MATLAB 's unzip Single File Hack

Using the code from MATLAB's unzip() and extractArchive() (which is called from unzip()), a custom function may be created to only extract a single file from a zip archive.

function [] = extractFile(zipFilename, outputDir, outputFile)
% extractFile

% Obtain the entry's output names
outputName = fullfile(outputDir, outputFile);

% Create a stream copier to copy files.
streamCopier = ...
    com.mathworks.mlwidgets.io.InterruptibleStreamCopier.getInterruptibleStreamCopier;

% Create a Java zipFile object and obtain the entries.
try
    % Create a Java file of the Zip filename.
    zipJavaFile = java.io.File(zipFilename);

    % Create a java ZipFile and validate it.
    zipFile = org.apache.tools.zip.ZipFile(zipJavaFile);

    % Get entry
    entry = zipFile.getEntry(outputFile);

catch exception
    if ~isempty(zipFile)
        zipFile.close;
    end
    delete(cleanUpUrl);
    error(message('MATLAB:unzip:unvalidZipFile', zipFilename));
end

% Create the Java File output object using the entry's name.
file = java.io.File(outputName);

% If the parent directory of the entry name does not exist, then create it.
parentDir = char(file.getParent.toString);
if ~exist(parentDir, 'dir')
    mkdir(parentDir)
end

% Create an output stream
try
    fileOutputStream = java.io.FileOutputStream(file);
catch exception
    overwriteExistingFile = file.isFile && ~file.canWrite;
    if overwriteExistingFile
        warning(message('MATLAB:extractArchive:UnableToOverwrite', outputName));
    else
        warning(message('MATLAB:extractArchive:UnableToCreate', outputName));
    end
    return
end

% Create an input stream from the API
fileInputStream = zipFile.getInputStream(entry);

% Extract the entry via the output stream.
streamCopier.copyStream(fileInputStream, fileOutputStream);

% Close the output stream.
fileOutputStream.close;

end