private String extractPackageName(FileDescriptorProto proto) {
        FileOptions options = proto.getOptions();
        if (options != null) {
            String javaPackage = options.getJavaPackage();
            if (!Strings.isNullOrEmpty(javaPackage)) {
                return javaPackage;
            }
        }

        return Strings.nullToEmpty(proto.getPackage());
    }
fetch the package name

@param proto
@return
compiler/src/main/java/com/alipay/sofa/gen/base/AbstractGenerator.java