public Jar setJarPrefix(Path file) {
        verifyNotSealed();
        if (jos != null)
            throw new IllegalStateException("Really executable cannot be set after entries are added.");
        if (file != null && jarPrefixStr != null)
            throw new IllegalStateException("A prefix has already been set (" + jarPrefixStr + ")");
        this.jarPrefixFile = file;
        return this;
    }
public Jar setJarPrefix ( Path file ) { verifyNotSealed ( ) ; if ( jos != null ) throw new IllegalStateException ( "Really executable cannot be set after entries are added." ) ; if ( file != null && jarPrefixStr != null ) throw new IllegalStateException ( "A prefix has already been set (" + jarPrefixStr + ")" ) ; this . jarPrefixFile = file ; return this ; }
Sets a file whose contents will be prepended to the JAR file's data.

@param file the prefix file, or {@code null} for none.
@return {@code this}