Java ZipInputStream

last modified July 15, 2022

Java ZipInputStream tutorial shows how to read ZIP files in Java with ZipInputStream.

Java ZipInputStream

ZipInputStream is a Java class that implements an input stream filter for reading files in the ZIP file format. It has support for both compressed and uncompressed entries.

ZIP

ZIP is an archive file format that supports lossless data compression. A ZIP file may contain one or more files or directories that may have been compressed. Java Archive (JAR) is built on the ZIP format.

ZipInputStream constructors

ZipInputStream has the following constructors:

ZipInputStream(InputStream in)
ZipInputStream(InputStream in, Charset charset)

ZipInputStream getNextEntry

The ZipInputStream's getNextEntry reads the next ZIP file entry and positions the stream at the beginning of the entry data.

Java read ZIP example

The following example reads the contents of a ZIP file.

package com.zetcode;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.IOException;
import java.time.LocalDate;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;

public class JavaReadZip {

    private final static Long MILLS_IN_DAY = 86400000L;

    public static void main(String[] args) throws IOException {

        String fileName = "src/resources/myfile.zip";

        try (FileInputStream fis = new FileInputStream(fileName);
                BufferedInputStream bis = new BufferedInputStream(fis);
                ZipInputStream zis = new ZipInputStream(bis)) {

            ZipEntry ze;

            while ((ze = zis.getNextEntry()) != null) {

                System.out.format("File: %s Size: %d last modified: %d",
                        ze.getName(), ze.getSize(),
                        LocalDate.ofEpochDay(ze.getTime() / MILLS_IN_DAY));
            }
        }
    }
}

The example reads the given ZIP file with ZipInputStream and prints its contents to the terminal. We print the file names, their size, and the last modification time.

String fileName = "src/resources/myfile.zip";

The ZIP file is located int src/resources/ directory.

try (FileInputStream fis = new FileInputStream(fileName);

We create a FileInputStream from the file. FileInputStream is used for reading streams of raw bytes.

BufferedInputStream bis = new BufferedInputStream(fis);

For better performance, we pass the FileInputStream into the BufferedInputStream.

ZipInputStream zis = new ZipInputStream(bis)) {

A ZipInputStream is created from the buffered FileInputStream. The try-with-resources closes the streams when they are not needed anymore.

while ((ze = zis.getNextEntry()) != null) {

In a while loop, we go through the entries of the ZIP file with getNextEntry method. It returns null if there are no more entries.

System.out.format("File: %s Size: %d last modified: %d",
    ze.getName(), ze.getSize(),
    LocalDate.ofEpochDay(ze.getTime() / MILLS_IN_DAY));

The getName returns the name of the entry, the getSize returns the uncompressed size of the entry, and the getTime returns the last modification time of the entry.

Java decompress ZIP example

In the next example, we decompress a ZIP file in Java.

package com.zetcode;

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;

public class JavaUnzip {

    public static void main(String args[]) throws Exception {

        byte[] buffer = new byte[2048];

        Path outDir = Paths.get("src/resources/output/");
        String zipFileName = "src/resources/myfile.zip";

        try (FileInputStream fis = new FileInputStream(zipFileName);
                BufferedInputStream bis = new BufferedInputStream(fis);
                ZipInputStream stream = new ZipInputStream(bis)) {

            ZipEntry entry;
            while ((entry = stream.getNextEntry()) != null) {

                Path filePath = outDir.resolve(entry.getName());

                try (FileOutputStream fos = new FileOutputStream(filePath.toFile());
                        BufferedOutputStream bos = new BufferedOutputStream(fos, buffer.length)) {

                    int len;
                    while ((len = stream.read(buffer)) > 0) {
                        bos.write(buffer, 0, len);
                    }
                }
            }
        }
    }
}

The example uses ZipInputStream to read the contents of the given ZIP file and FileOutputStream and BufferedOutputStream to write the contents into a directory.

Path outDir = Paths.get("src/resources/output/");

This is the directory where we extract the contents of the ZIP file.

while ((entry = stream.getNextEntry()) != null) {

In the first while loop, we go through the entries of the ZIP file.

while ((len  = stream.read(buffer)) > 0) {
    bos.write(buffer, 0, len);
}

In the second while loop, we read the entries and write them to the output stream.

Source

Java ZipInputStream - language reference

In this article we have presented the Java ZipInputStream class. We have created two examples to read a ZIP file and to decompress a ZIP file.

Author

My name is Jan Bodnar and I am a passionate programmer with many years of programming experience. I have been writing programming articles since 2007. So far, I have written over 1400 articles and 8 e-books. I have over eight years of experience in teaching programming.

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