Decode Base64 encoded ZIP archive (GZIP)

Question

I need to decode a Base64 encoded ZIP archive (GZIP) String in Java.

String = "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"

We don't do your job; we try to help if you've tried something and have a problem. — Abhijit Sarkar
Hint: decode the string with either DatatypeConverter.parseBase64Binary() or Base64.getDecoder().decode() (java 8), then use GZIPInputStream with ByteArrayInputStream... You've not said what underlying data is, and that string isn't valid base64 so can't help you any further... — Adam
Hey @Adam, What do you mean by the String is not a valid base64 String? Can you please explain me? — navrani
The standard Java Base64 decoding utilities reported an error when I tried to decode it... "Input byte array has wrong 4-byte ending unit" — Adam

navrani navrani · Accepted Answer · 2017-08-24T06:44:08

import com.sun.org.apache.xml.internal.security.exceptions.Base64DecodingException;
import com.sun.org.apache.xml.internal.security.utils.Base64;
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.util.zip.GZIPInputStream;

public class GzipUtil {
    public static void unzip() throws Base64DecodingException {
        String encoded = "PUT BASE 64ENCODED GZIPPED STRING HERE";
        byte[] compressed = Base64.decode(encoded);
        String data = new String(compressed);
        //System.out.println(data);AAAA";

        if ((compressed == null) || (compressed.length == 0)) {
            throw new IllegalArgumentException("Cannot unzip null or empty bytes");
        }
        if (!isZipped(compressed)) {
            System.out.println(compressed);
        }

        try (ByteArrayInputStream byteArrayInputStream = new ByteArrayInputStream(compressed)) {
            try (GZIPInputStream gzipInputStream = new GZIPInputStream(byteArrayInputStream)) {
                try (InputStreamReader inputStreamReader =
                             new InputStreamReader(gzipInputStream, StandardCharsets.UTF_8)) {
                    try (BufferedReader bufferedReader = new BufferedReader(inputStreamReader)) {
                        StringBuilder output = new StringBuilder();
                        String line;
                        while ((line = bufferedReader.readLine()) != null) {
                            output.append(line);
                            System.out.println(output.toString());
                        }
                    }
                }
            }
        } catch (IOException e) {
            throw new RuntimeException("Failed to unzip content", e);
        }
    }

    public static boolean isZipped(final byte[] compressed) {
        return (compressed[0] == (byte) (GZIPInputStream.GZIP_MAGIC))
                && (compressed[1] == (byte) (GZIPInputStream.GZIP_MAGIC >> 8));
    }
}

Decode Base64 encoded ZIP archive (GZIP)

1 Answers