How do I read a zip file checksum value?

package org.kodejava.example.util;

import java.io.*;
import java.util.zip.ZipInputStream;
import java.util.zip.ZipEntry;
import java.util.zip.CheckedInputStream;
import java.util.zip.Adler32;

public class UnzipWithChecksum {
    public static void main(String[] args) {
        String zipname = "data-1.zip";

        try {
            FileInputStream fis = new FileInputStream(zipname);

            //
            // Creating input stream that also maintains the checksum of the
            // data which later can be used to validate data integrity.
            //
            CheckedInputStream checksum = new CheckedInputStream(fis, new Adler32());
            ZipInputStream zis = new ZipInputStream(new BufferedInputStream(checksum));
            ZipEntry entry;

            //
            // Read each entry from the ZipInputStream until no more entry found
            // indicated by a null return value of the getNextEntry() method.
            //
            while ((entry = zis.getNextEntry()) != null) {
                System.out.println("Unzipping: " + entry.getName());

                int size;
                byte[] buffer = new byte[2048];

                FileOutputStream fos = new FileOutputStream(entry.getName());
                BufferedOutputStream bos = new BufferedOutputStream(fos, buffer.length);

                while ((size = zis.read(buffer, 0, buffer.length)) != -1) {
                    bos.write(buffer, 0, size);
                }
                bos.flush();
                bos.close();
            }

            zis.close();
            fis.close();

            //
            // Print out the checksum value
            //
            System.out.println("Checksum = " + checksum.getChecksum().getValue());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I create checksum for a zip file?

This example demonstrate how to use CheckedOutputStream for creating a checksum of a zip file. Checksum can be used to detect whether a data was corrupted during a transmission process to a remote machine.

package org.kodejava.example.util;

import java.io.*;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;
import java.util.zip.CheckedOutputStream;
import java.util.zip.Adler32;

public class ZipWithChecksum {
    public static void main(String[] args) {
        try {
            String target = "data-1.zip";

            FileOutputStream fos = new FileOutputStream(target);

            //
            // An output stream that also maintains a checksum of the data being
            // written. The checksum can then be used to verify the integrity of
            // the output data.
            //
            CheckedOutputStream checksum = new CheckedOutputStream(fos, new Adler32());
            ZipOutputStream zos = new ZipOutputStream(new BufferedOutputStream(checksum));

            int size = 0;
            byte[] buffer = new byte[1024];

            //
            // Get all text files on the working folder.
            //
            File dir = new File(".");
            String[] files = dir.list(new FilenameFilter() {
                public boolean accept(File dir, String name) {
                    if (name.endsWith(".txt")) {
                        return true;
                    } else {
                        return false;
                    }
                }
            });

            for (int i = 0; i < files.length; i++) {
                System.out.println("Compressing: " + files[i]);

                FileInputStream fis = new FileInputStream(files[i]);
                BufferedInputStream bis = new BufferedInputStream(fis, buffer.length);

                // put a new ZipEntry in the ZipOutputStream
                ZipEntry zipEntry = new ZipEntry(files[i]);
                zos.putNextEntry(zipEntry);

                // read data to the end of the source file and write it to the zip
                // output stream.
                while ((size = fis.read(buffer, 0, buffer.length)) > 0) {
                    zos.write(buffer, 0, size);
                }

                zos.closeEntry();
                fis.close();
            }

            // Finish zip process
            zos.close();

            //
            // Print out checksum value
            //
            System.out.println("Checksum   : " + checksum.getChecksum().getValue());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I decompress a zip file using ZipFile?

In this example we use the java.util.zip.ZipFile class to decompress and extract a zip file.

package org.kodejava.example.util.zip;

import java.util.zip.ZipFile;
import java.util.zip.ZipEntry;
import java.util.Enumeration;
import java.io.*;

public class ZipFileUnzipDemo {
    public static void main(String[] args) {
        String zipname = "data.zip";

        try {
            ZipFile zipFile = new ZipFile(zipname);
            Enumeration enumeration = zipFile.entries();

            while (enumeration.hasMoreElements()) {
                ZipEntry zipEntry = (ZipEntry) enumeration.nextElement();
                System.out.println("Unzipping: " + zipEntry.getName());

                BufferedInputStream bis = new BufferedInputStream(zipFile.getInputStream(zipEntry));

                int size;
                byte[] buffer = new byte[2048];

                FileOutputStream fos = new FileOutputStream(zipEntry.getName());
                BufferedOutputStream bos = new BufferedOutputStream(fos, buffer.length);

                while ((size = bis.read(buffer, 0, buffer.length)) != -1) {
                    bos.write(buffer, 0, size);
                }

                bos.flush();
                bos.close();
                fos.close();

                bis.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I decompress a zip file using ZipInputStream?

The code below shows how to decompress and extract files from a zip archive. In the example we use the java.util.zip.ZipInputStream class.

package org.kodejava.example.util.zip;

import java.io.*;
import java.util.zip.ZipInputStream;
import java.util.zip.ZipEntry;

public class UnzipDemo {
    public static void main(String[] args) {
        String zipName = "data.zip";

        try {
            FileInputStream fis = new FileInputStream(zipName);
            ZipInputStream zis = new ZipInputStream(
                    new BufferedInputStream(fis));
            ZipEntry entry;

            //
            // Read each entry from the ZipInputStream until no
            // more entry found indicated by a null return value
            // of the getNextEntry() method.
            //
            while ((entry = zis.getNextEntry()) != null) {
                System.out.println("Unzipping: " + entry.getName());

                int size;
                byte[] buffer = new byte[2048];

                FileOutputStream fos =
                        new FileOutputStream(entry.getName());
                BufferedOutputStream bos =
                        new BufferedOutputStream(fos, buffer.length);

                while ((size = zis.read(buffer, 0, buffer.length)) != -1) {
                    bos.write(buffer, 0, size);
                }
                bos.flush();
                bos.close();
            }

            zis.close();
            fis.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

How do I create a zip file?

package org.kodejava.example.util.zip;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;

public class ZippingFileExample {
    public static void main(String[] args) {
        String source = "data.txt";
        String target = "data.zip";

        try {
            ZipOutputStream zos = new ZipOutputStream(
                    new FileOutputStream(target));

            // Create input stream to read file from resource folder.
            Class clazz = ZippingFileExample.class;
            InputStream is = clazz.getResourceAsStream("/" + source);

            // Put a new ZipEntry in the ZipOutputStream
            zos.putNextEntry(new ZipEntry(source));

            int size;
            byte[] buffer = new byte[1024];

            // Read data to the end of the source file and write it
            // to the zip output stream.
            while ((size = is.read(buffer, 0, buffer.length)) > 0) {
                zos.write(buffer, 0, size);
            }

            zos.closeEntry();
            is.close();

            // Finish zip process
            zos.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}