Zip folder with java

Java Zip and Unzip Files and Folders

Here we will learn about how to zip and unzip files and folders in java.

If information contains redundant data it will be tough to store and transfer the data. So we will go for compression which will give efficient representation of the data. For zipping many algorithms are there.

Java provides the java.util.zip package for zipping and unzipping the files. The class ZipOutputStream will be useful for compressing. It is an output stream filter which will write files to any File output stream in zip format. The class ZipInputStream will be useful for decompressing. It is an input stream which will read files that are in zip format.

How to Zip Files in Java?

For zipping purpose we have many algorithms. If we are not mentioning any alogorithm through any method it will use default compression method that is DEFLATED compression. Deflated compression is almost near to Huffman coding.

Now we will see one example.

Problem: We want to zip the directory which has multiple files along with sub folders.

Solution: Zipping a file is very easy. But when we are zipping a folder which contains sub folders we should take care about the relative paths of files which have to be zipped.

For example take directory named as first which is located in E disk. It contains one subfolder along with multiple files. We have to zip it now.

Step 1: We should list out all files in the directory. listFiles() method will return total files (directories + files) in that directory. We can use this method to list out the total files. For this we have to check whether it is a directory or not. If it is a directory then again list out the files in that subdirectory. Continue this process until all files are listed out. This is recursive process.

Step 2: After listing out the files, we should create a file output stream for output zip folder. So that it will create output zip folder and write the contents to it.

Step 3: We should create a zip output stream which will write file contents to the file output stream in the format of zip.

• Create an input stream for a file. So that it can read file contents.
• Create a zip Entry object for file with relative path only because if use absolute path it can’t find files so zipping is not possible. So that we can add this file to zip out stream. For adding putNextEntry() method of ZipOutputStream will be useful.
• Now zip output stream will write these file contents in the format of zip to the file output stream.
• Close zip entry and close file input stream

This is the process of zipping one file. So do the same for every file in the list.

Step 5: As zipping of all files is done. Now close all IO streams. Proper closing of IO streams will prevent the corruption of zip files.

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Zipping and Unzipping in Java

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We’re looking for a new Java technical editor to help review new articles for the site.

1. Overview

In this quick tutorial, we’ll learn how to zip a file into an archive and how to unzip the archive, all using core libraries provided by Java.

These core libraries are part of the java.util.zip package, where we can find all zipping- and unzipping-related utilities.

2. Zip a File

First, let’s look at a simple operation, zipping a single file.

For example, we’ll zip a file named test1.txt into an archive named compressed.zip.

Of course, we’ll first access the file from a disk:

public class ZipFile < public static void main(String[] args) throws IOException < String sourceFile = "test1.txt"; FileOutputStream fos = new FileOutputStream("compressed.zip"); ZipOutputStream zipOut = new ZipOutputStream(fos); File fileToZip = new File(sourceFile); FileInputStream fis = new FileInputStream(fileToZip); ZipEntry zipEntry = new ZipEntry(fileToZip.getName()); zipOut.putNextEntry(zipEntry); byte[] bytes = new byte[1024]; int length; while((length = fis.read(bytes)) >= 0) < zipOut.write(bytes, 0, length); >zipOut.close(); fis.close(); fos.close(); > >

3. Zip Multiple Files

Next, let’s see how to zip multiple files into one zip file. We’ll compress test1.txt and test2.txt into multiCompressed.zip:

public class ZipMultipleFiles < public static void main(String[] args) throws IOException < String file1 = "src/main/resources/zipTest/test1.txt"; String file2 = "src/main/resources/zipTest/test2.txt"; final ListsrcFiles = Arrays.asList(file1, file2); final FileOutputStream fos = new FileOutputStream(Paths.get(file1).getParent().toAbsolutePath() + "/compressed.zip"); ZipOutputStream zipOut = new ZipOutputStream(fos); for (String srcFile : srcFiles) < File fileToZip = new File(srcFile); FileInputStream fis = new FileInputStream(fileToZip); ZipEntry zipEntry = new ZipEntry(fileToZip.getName()); zipOut.putNextEntry(zipEntry); byte[] bytes = new byte[1024]; int length; while((length = fis.read(bytes)) >= 0) < zipOut.write(bytes, 0, length); >fis.close(); > zipOut.close(); fos.close(); > >

4. Zip a Directory

Now, let’s discuss how to zip an entire directory. Here, we’ll compress the zipTest folder into the dirCompressed.zip file:

public class ZipDirectory < public static void main(String[] args) throws IOException < String sourceFile = "zipTest"; FileOutputStream fos = new FileOutputStream("dirCompressed.zip"); ZipOutputStream zipOut = new ZipOutputStream(fos); File fileToZip = new File(sourceFile); zipFile(fileToZip, fileToZip.getName(), zipOut); zipOut.close(); fos.close(); >private static void zipFile(File fileToZip, String fileName, ZipOutputStream zipOut) throws IOException < if (fileToZip.isHidden()) < return; >if (fileToZip.isDirectory()) < if (fileName.endsWith("/")) < zipOut.putNextEntry(new ZipEntry(fileName)); zipOut.closeEntry(); >else < zipOut.putNextEntry(new ZipEntry(fileName + "/")); zipOut.closeEntry(); >File[] children = fileToZip.listFiles(); for (File childFile : children) < zipFile(childFile, fileName + "/" + childFile.getName(), zipOut); >return; > FileInputStream fis = new FileInputStream(fileToZip); ZipEntry zipEntry = new ZipEntry(fileName); zipOut.putNextEntry(zipEntry); byte[] bytes = new byte[1024]; int length; while ((length = fis.read(bytes)) >= 0) < zipOut.write(bytes, 0, length); >fis.close(); > >

• To zip sub-directories, we iterate through them recursively.
• Every time we find a directory, we append its name to the descendant’s ZipEntry name to save the hierarchy.
• We also create a directory entry for every empty directory.

5. Append New Files to Zip File

Next, we’ll add a single file to an existing zip file. For example, let’s add file3.txt into compressed.zip:

String file3 = "src/main/resources/zipTest/file3.txt"; Map env = new HashMap<>(); env.put("create", "true"); Path path = Paths.get(Paths.get(file3).getParent() + "/compressed.zip"); URI uri = URI.create("jar:" + path.toUri()); try (FileSystem fs = FileSystems.newFileSystem(uri, env))

In short, we mounted the zip file using .newFileSystem() provided by the FileSystems class, which has been available since JDK 1.7. Then, we created a newFile3.txt inside the compressed folder and added all the contents from file3.txt.

6. Unzip an Archive

Now, let’s unzip an archive and extract its contents.

For this example, we’ll unzip compressed.zip into a new folder named unzipTest:

public class UnzipFile < public static void main(String[] args) throws IOException < String fileZip = "src/main/resources/unzipTest/compressed.zip"; File destDir = new File("src/main/resources/unzipTest"); byte[] buffer = new byte[1024]; ZipInputStream zis = new ZipInputStream(new FileInputStream(fileZip)); ZipEntry zipEntry = zis.getNextEntry(); while (zipEntry != null) < // . >zis.closeEntry(); zis.close(); > >

Inside the while loop, we’ll iterate through each ZipEntry and first check if it’s a directory. If it is, then we’ll create the directory using the mkdirs() method; otherwise, we’ll continue with creating the file:

while (zipEntry != null) < File newFile = newFile(destDir, zipEntry); if (zipEntry.isDirectory()) < if (!newFile.isDirectory() && !newFile.mkdirs()) < throw new IOException("Failed to create directory " + newFile); >> else < // fix for Windows-created archives File parent = newFile.getParentFile(); if (!parent.isDirectory() && !parent.mkdirs()) < throw new IOException("Failed to create directory " + parent); >// write file content FileOutputStream fos = new FileOutputStream(newFile); int len; while ((len = zis.read(buffer)) > 0) < fos.write(buffer, 0, len); >fos.close(); > zipEntry = zis.getNextEntry(); >

One note here is that on the else branch, we’re also checking if the file’s parent directory exists. This is necessary for archives created on Windows, where the root directories don’t have a corresponding entry in the zip file.

Another critical point is in the newFile() method:

public static File newFile(File destinationDir, ZipEntry zipEntry) throws IOException < File destFile = new File(destinationDir, zipEntry.getName()); String destDirPath = destinationDir.getCanonicalPath(); String destFilePath = destFile.getCanonicalPath(); if (!destFilePath.startsWith(destDirPath + File.separator)) < throw new IOException("Entry is outside of the target dir: " + zipEntry.getName()); >return destFile; >

The newFile() method guards against writing files to the file system outside the target folder. This vulnerability is called Zip Slip.

7. Conclusion

In this article, we illustrated how to use Java libraries for zipping and unzipping files.

The implementation of these examples can be found over on GitHub.

Slow MySQL query performance is all too common. Of course it is. A good way to go is, naturally, a dedicated profiler that actually understands the ins and outs of MySQL.

The Jet Profiler was built for MySQL only, so it can do things like real-time query performance, focus on most used tables or most frequent queries, quickly identify performance issues and basically help you optimize your queries.

Critically, it has very minimal impact on your server’s performance, with most of the profiling work done separately — so it needs no server changes, agents or separate services.

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