in src/main/java/org/apache/maven/plugins/jarsigner/JarsignerSignMojo.java [258:266]
protected void preProcessArchive(final File archive) throws MojoExecutionException {
if (removeExistingSignatures) {
try {
JarSignerUtil.unsignArchive(archive);
} catch (IOException e) {
throw new MojoExecutionException("Failed to unsign archive " + archive + ": " + e.getMessage(), e);
}
}
}