Question

How we check whether zip file corrupted or valid Zip file before going to extract it

my code`

import java.io.IOException;
import java.io.OutputStream;
import java.util.zip.ZipEntry;
import java.util.zip.ZipInputStream;

public void unzip() {
        FileInputStream fin = null;
        ZipInputStream zin = null;
        OutputStream fout = null;

    File outputDir = new File(_location);
    File tmp = null;

    try {
        fin = new FileInputStream(_zipFile);
        zin = new ZipInputStream(fin);
        ZipEntry ze = null;
        while ((ze = zin.getNextEntry()) != null) {
            Log.d("Decompress", "Unzipping " + ze.getName());

            if (ze.isDirectory()) {
                dirChecker(ze.getName());
            } else {
                tmp = File.createTempFile( "decomp", ".tmp", outputDir );
                fout = new BufferedOutputStream(new FileOutputStream(tmp));
                DownloadFile.copyStream( zin, fout, _buffer, BUFFER_SIZE );
                zin.closeEntry();
                fout.close();
                fout = null;
                tmp.renameTo( new File(_location + ze.getName()) );
                tmp = null; 
            }
        }
        zin.close();
        zin = null;
    } catch (IOException e) {
        throw new RuntimeException(e);
    } finally {
        if ( tmp != null  ) { try { tmp.delete();     } catch (Exception ignore) {;} }
        if ( fout != null ) { try { fout.close();     } catch (Exception ignore) {;} }
        if ( zin != null  ) { try { zin.closeEntry(); } catch (Exception ignore) {;} }
        if ( fin != null  ) { try { fin.close();      } catch (Exception ignore) {;} }
    }
}

`

this work fine with valid zipfile, but invalid zipfile it doesen’t throw any exception not produce anything, but i need to confirm the validity of zip file before going to unzip it

Answer 1

I think it’s pretty much useless for checking if the zip file is corrupted for two reasons:

1. Some zip files contain more bytes than just the zip part. For example, self-extracting archives have an executable part yet they’re still valid zip.
2. The file can be corrupted without changing its size.

So, I suggest calculating the CRC for a guaranteed method of checking for corruption.