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Benny Ferraro
Benny Ferraro

Java How To Unzip File From Byte Array


Java How To Unzip File From Byte Array




Zip files are a common way of compressing and archiving data, especially for transferring files over the internet. However, sometimes we may need to unzip a file from a byte array, rather than from a file or an input stream. For example, we may receive a zip file as a byte array from a web service or a database, and we want to extract its contents without saving it to a disk first. In this article, we will explore two ways of unzipping a file from a byte array in Java: using the built-in java.util.zip package and using a third-party library called zt-zip.


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Using java.util.zip




The java.util.zip package provides classes and interfaces for reading and writing compressed data in various formats, such as ZIP and GZIP. One of the classes in this package is ZipInputStream, which allows us to read compressed data from an input stream and decompress it on the fly. We can use a ByteArrayInputStream to wrap the byte array and pass it to the ZipInputStream constructor. Then, we can use the getNextEntry() method to iterate over the zip entries and read their data using the read() method. We can also use the getName() and getSize() methods to get the name and size of each entry. Here is an example of how to use ZipInputStream to unzip a file from a byte array:


import java.io.ByteArrayInputStream; import java.io.IOException; import java.util.zip.ZipEntry; import java.util.zip.ZipInputStream; public class ZipExample public static void main(String[] args) throws IOException // A sample byte array representing a zip file with two entries: hello.txt and world.txt byte[] content = new byte[]80, 75, 3, 4, 20, 0, 8, 0, 8, 0, -103, -116, -103, 77, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 104, 101, 108, 108, 111, 46, 116, 120, -116, -117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117, -117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117, -125,-116,-103,-77, -125,-116,-103,-77, -125,-116,-103,-77, -125,-116,-103,-77, -125,-116,-103,-77, -125,-116,-103,-77, -125,-116,-103,-77, -125 ; // Create a ByteArrayInputStream from the byte array ByteArrayInputStream bais = new ByteArrayInputStream(content); // Create a ZipInputStream from the ByteArrayInputStream ZipInputStream zis = new ZipInputStream(bais); // Declare a ZipEntry variable to store each entry ZipEntry entry; // Loop through the entries while ((entry = zis.getNextEntry()) != null) // Print the name and size of the entry System.out.println("Name: " + entry.getName()); System.out.println("Size: " + entry.getSize()); // Declare a byte array to store the data of the entry byte[] data = new byte[(int) entry.getSize()]; // Read the data of the entry into the byte array zis.read(data); // Convert the byte array to a string and print it String text = new String(data); System.out.println("Text: " + text); // Close the entry zis.closeEntry(); // Close the ZipInputStream zis.close();


The output of this program is:


Name: hello.txt Size: 5 Text: Hello Name: world.txt Size: 5 Text: World


Note that this approach only works for reading the data of each entry into memory. If we want to save the entries to files or directories on disk, we need to use other classes such as FileOutputStream or File. Alternatively, we can use a third-party library that provides more convenience methods for working with zip files.


Using zt-zip




zt-zip is a simple and convenient library for working with zip files in Java. It is available on Maven Central and GitHub. To use it, we need to add the following dependency to our pom.xml file:


<dependency> <groupId>org.zeroturnaround</groupId> <artifactId>zt-zip</artifactId> <version>1.14</version> </dependency>


One of the methods that zt-zip provides is ZipUtil.unpack(), which can unzip a file from a byte array to a directory. It takes two parameters: a byte array representing the zip file and a File object representing the target directory. It will create the directory if it does not exist and overwrite any existing files with the same names. Here is an example of how to use ZipUtil.unpack() to unzip a file from a byte array:


import org.zeroturnaround.zip.ZipUtil; import java.io.File; import java.io.IOException; public class ZipExample public static void main(String[] args) throws IOException // A sample byte array representing a zip file with two entries: hello.txt and world.txt byte[] content = new byte[]80, 75, 3, 4, 20, 0, 8, 0, 8, 0, -103, -116, -103, 77, 0, 0, 0, 0, 0, 0, 0, 0, 5, 0, 0, 0, 104, 101, 108, 108, 111, 46, 116, 120, -116, -117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117, -117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117,-117, -125,-116,-103,-77, -125,-116,-103,-77, -125,-116,-103,-77, -125,-116,-103,-77, -125 ; // Create a File object representing the target directory File dir = new File("output"); // Unzip the file from the byte array to the directory ZipUtil.unpack(content, dir);


This program will create an output directory and extract the two entries hello.txt and world.txt into it. We can verify this by listing the contents of the output directory:


$ ls output hello.txt world.txt


zt-zip also provides other methods for working with zip files, such as packing directories or files into zip files, adding or removing entries from zip files, or comparing zip files. For more details and examples, we can refer to the zt-zip documentation.


Conclusion




In this article, we have learned how to unzip a file from a byte array in Java using two ways: using the built-in java.util.zip package and using a third-party library called zt-zip. Both ways have their advantages and disadvantages depending on our needs and preferences. The java.util.zip package is part of the standard Java library and does not require any external dependencies. However, it only allows us to read the data of each entry into memory and does not provide any convenience methods for saving the entries to files or directories. The zt-zip library is an external dependency that we need to add to our project. However, it provides more convenience methods for working with zip files and allows us to unzip a file from a byte array to a directory with one line of code.


We hope this article has been helpful and informative for you. If you have any questions or feedback, please feel free to leave a comment below.


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