Append a file into existing ZIP using Java

 

The following code reads a input file 'in.zip' appends 'abc.txt' with some String content into it and creates output zip file 'out.zip' using Java.

import java.io.ByteArrayOutputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;
import java.time.LocalDateTime;
import java.util.zip.ZipOutputStream;

public class ZipTests {

    public static void main(String[] args) throws Exception {
        var zipFile = new java.util.zip.ZipFile("in.zip");
        final var zos = new ZipOutputStream(new FileOutputStream("out.zip"));
        for (var e = zipFile.entries(); e.hasMoreElements(); ) {
            var entryIn = e.nextElement();
            System.out.println("Processing entry " + entryIn.getName());

            //need to set next entry before modifying /adding content
            zos.putNextEntry(entryIn);

            if (entryIn.getName().equalsIgnoreCase("abc.txt")) {
                //modify content and save to output zip stream

                String content = isToString(zipFile.getInputStream(entryIn));
                content = content.replaceAll("key1=value1", "key1=val2");
                content += LocalDateTime.now() + "\r\n";

                byte[] buf = content.getBytes();
                zos.write(buf, 0, buf.length);
            } else {
                //copy the content
                var inputStream = zipFile.getInputStream(entryIn);
                byte[] buf = new byte[9096];
                int len;
                while ((len = inputStream.read(buf)) > 0) {
                    zos.write(buf, 0, len);
                }

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

    static String isToString(InputStream stringStream) throws Exception {
        var result = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024];
        for (int length; (length = stringStream.read(buffer)) != -1; ) {
            result.write(buffer, 0, length);
        }
        return result.toString(StandardCharsets.UTF_8);
    }

}