How to update a JAR file entry from https://subversivebytes.wordpress.com/2012/10/11/java-programmatically-update-jar-file/

gistfile1.txt

public void updateJarFile(File srcJarFile, String targetPackage, File ...filesToAdd) throws IOException {
    File tmpJarFile = File.createTempFile("tempJar", ".tmp");
    JarFile jarFile = new JarFile(srcJarFile);
    boolean jarUpdated = false;
 
    try {
        JarOutputStream tempJarOutputStream = new JarOutputStream(new FileOutputStream(tmpJarFile));
 
        try {
            //Added the new files to the jar.
            for(int i=0; i < filesToAdd.length; i++) {
                File file = filesToAdd[i];
                FileInputStream fis = new FileInputStream(file);
                try {
                    byte[] buffer = new byte[1024];
                    int bytesRead = 0;
                    JarEntry entry = new JarEntry(targetPackage+File.separator+file.getName());
                    tempJarOutputStream.putNextEntry(entry);
                    while((bytesRead = fis.read(buffer)) != -1) {
                        tempJarOutputStream.write(buffer, 0, bytesRead);
                    }
 
                    //System.out.println(entry.getName() + " added.");
                }
                finally {
                    fis.close();
                }
            }
 
            //Copy original jar file to the temporary one.
            Enumeration jarEntries = jarFile.entries();
            while(jarEntries.hasMoreElements()) {
                JarEntry entry = jarEntries.nextElement();
                InputStream entryInputStream = jarFile.getInputStream(entry);
                tempJarOutputStream.putNextEntry(entry);
                byte[] buffer = new byte[1024];
                int bytesRead = 0;
                while ((bytesRead = entryInputStream.read(buffer)) != -1) {
                    tempJarOutputStream.write(buffer, 0, bytesRead);
                }
            }
 
            jarUpdated = true;
        }
        catch(Exception ex) {
            ex.printStackTrace();
            tempJarOutputStream.putNextEntry(new JarEntry("stub"));
        }
        finally {
            tempJarOutputStream.close();
        }
 
    }
    finally {
        jarFile.close();
        //System.out.println(srcJarFile.getAbsolutePath() + " closed.");
 
        if (!jarUpdated) {
            tmpJarFile.delete();
        }
    }
 
    if (jarUpdated) {
        srcJarFile.delete();
        tmpJarFile.renameTo(srcJarFile);
        //System.out.println(srcJarFile.getAbsolutePath() + " updated.");
    }
}