Welcome!

Eclipse Authors: Pat Romanski, Elizabeth White, Liz McMillan, David H Deans, JP Morgenthal

Related Topics: IBM Cloud, Java IoT, Adobe Flex, Open Source Cloud, Eclipse, Machine Learning

IBM Cloud: Article

Reflections on Java Command Line Options

There are many different types of command line options that programs need to recognize

Abstract
There are many different types of command line options that programs need to recognize. Many languages (e.g.: bash and perl) has built-in processing of command line options; Java does not. The Java Command Line Options (JCLO) package performs this task for a variety of option styles. It also uses Java's reflection capability to automatically assign values to variables in a specified class.

Introduction
Even in these days of sophisticated graphical user interfaces, many programs have a wide variety of command line options that help specify their behavior. It is also the case that command line only programs continue to enjoy wide use. It is also the case the command line arguments can become quite complicated, e.g.: -Djava.util.logging.config.file=All.finest -1 --list --this=that Some languages have built-in parsers for command line options; perl and bash are two obvious examples of this. Java has no such parser built in. The JCLO package provides the capability to parse several different command line option formats, and uses Java's reflecion mechanizm to both drive the parsing and assign the values provided by command line options to the variable in a specified class.

Brief overview of command line option formats
UNIX command line options started with a simple "dash and letter" format. "ls -l" is a classic example. If the option specified an additional option, the dash and letter were followed by a space and the additional option. "sort -t separator" is and example. UNIX also allowed the use of numbers, "ls -1", as options. As the number of possible option proliferated, and newer "GNU" style was developed. These have a "double dash/long name" style: "sort --version" for example. When additional options are needed for this style, it is typically provided with a "equals value" style: "gcc --std=c89". Finally, Java has its own style of "single dash/name with dots/equals value" style: "-Djava.util.logging.config.file=logging.props".

Specifying non-Java variable name options
JCLO uses Java reflection to extract variable names as the basis for parsing command line options. Not all styles just described are valid Java variable names and therefore JCLO uses several conventions to allow them specified. Java variables must begin with an alphabetic character or an underscore, numbers are not allowed to start a variable name. Variable names cannot contain dashes, as dashes specify subtraction or negation. They cannot contain dots as dots specify class references or decimal literals. Therefore, JCLO uses the convention of prefixing number options with an underscore (_1). For dashes embedded in options (e.g.: "--font-size=10"), JCLO uses two underscores ("font__size") in the variable name. For the embedded dots, JCLO uses a convention of an underscore followed by a dollar sign "_$".

Brief review of Java reflection
Java, as with other object oriented languages, has the ability to query and modify an object's internal information. One can retrieve a Class's constructors, methods, fields, etc. JCLO uses the getDeclaredFields()" method on a class to find the names it will accept and set the value for. One can either have a single class devoted to command line options or specify a prefix for the variables JCLO's will examine.

From class variables to command line options
First let's look at an example to see how JCLO works in practice. We have the obligatory import:

import edu.mscd.cs.jclo.JCLO;

and then we create a class whose class varibles will become the command line options:

class ExampleArgs
{
    private int a;
    private boolean b;
    private float c;
    private String d;
    private String[] additional;
}

A simple main will be used to illustrate JCLO's operation:

public class Example
{
    public static void main (String args[])
    {
        ExampleArgs ea = new ExampleArgs();
        JCLO jclo = new JCLO (ea);
        jclo.parse (args);
	System.out.println ("a = " + ea.a);
	System.out.println ("b = " + ea.b);
	System.out.println ("c = " + ea.c);
	System.out.println ("d = " + ea.d);
	System.out.println ("additional = " + 
	    java.util.Arrays.toString (ea.additional));
    }
}

First, an object that contains the variables whose values will be assigned by the command line options is created. This object is then used to create a JCLO object. The parse method is then called with the command line options to do the actual work Running this simple program with the following command line options:

java -cp .:JCLO-1.3.4.jar Example -a 5 --b=true --c=9.0 -d Example one two three

produces:

a = 5
b = true
c = 9.0
d = Example
additional = [one, two, three]

Here, each of the class varibles where assigned values from the associated command line option. The additional String array is assigned any options beyond the last dash option. JCLO can also use only certain fields of an object by the programmer specifying a string prefix that those fields begin with.

There are times when command line options have aliases; for example a long and short version. JCLO has the ability to deal with these directly. Adding

String aliases[][] ={{"boolean", "b"}};

and modifying

JCLO jclo = new JCLO (ea, aliases);

to the above example allows for --boolean to set the value for b

:

java -cp .:JCLO-1.3.4.jar Example --boolean
a = 0
b = true
c = 0.0
d = null
additional = null

JCLO also has a simple usage() method that returns a String of possible options and the type of values they require.

Conclusion
JCLO allows one to easily parse command line options and set the values inside a class based on those options. It is very flexible in its parsing, allowing intermixed single- and double-dashed options, along with aliases that allow long and short versions of an option. JCLO is available from http://jclo.sourceforge.net/.

More Stories By Steve Beaty

Steve has an extensive background in both the theoretic and pragmatic aspects of computer science. He wrote compilers at Cray Computer, and both managed a large group of developers and was a software test architect at HP. He has a number of active open-source projects and is a professor of computer science at the Metropolitan State College of Denver.

@ThingsExpo Stories
In a recent survey, Sumo Logic surveyed 1,500 customers who employ cloud services such as Amazon Web Services (AWS), Microsoft Azure, and Google Cloud Platform (GCP). According to the survey, a quarter of the respondents have already deployed Docker containers and nearly as many (23 percent) are employing the AWS Lambda serverless computing framework. It’s clear: serverless is here to stay. The adoption does come with some needed changes, within both application development and operations. Tha...
As hybrid cloud becomes the de-facto standard mode of operation for most enterprises, new challenges arise on how to efficiently and economically share data across environments. In his session at 21st Cloud Expo, Dr. Allon Cohen, VP of Product at Elastifile, will explore new techniques and best practices that help enterprise IT benefit from the advantages of hybrid cloud environments by enabling data availability for both legacy enterprise and cloud-native mission critical applications. By rev...
In his Opening Keynote at 21st Cloud Expo, John Considine, General Manager of IBM Cloud Infrastructure, will lead you through the exciting evolution of the cloud. He'll look at this major disruption from the perspective of technology, business models, and what this means for enterprises of all sizes. John Considine is General Manager of Cloud Infrastructure Services at IBM. In that role he is responsible for leading IBM’s public cloud infrastructure including strategy, development, and offering ...
SYS-CON Events announced today that Ryobi Systems will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Ryobi Systems Co., Ltd., as an information service company, specialized in business support for local governments and medical industry. We are challenging to achive the precision farming with AI. For more information, visit http:...
Amazon is pursuing new markets and disrupting industries at an incredible pace. Almost every industry seems to be in its crosshairs. Companies and industries that once thought they were safe are now worried about being “Amazoned.”. The new watch word should be “Be afraid. Be very afraid.” In his session 21st Cloud Expo, Chris Kocher, a co-founder of Grey Heron, will address questions such as: What new areas is Amazon disrupting? How are they doing this? Where are they likely to go? What are th...
High-velocity engineering teams are applying not only continuous delivery processes, but also lessons in experimentation from established leaders like Amazon, Netflix, and Facebook. These companies have made experimentation a foundation for their release processes, allowing them to try out major feature releases and redesigns within smaller groups before making them broadly available. In his session at 21st Cloud Expo, Brian Lucas, Senior Staff Engineer at Optimizely, will discuss how by using...
In this strange new world where more and more power is drawn from business technology, companies are effectively straddling two paths on the road to innovation and transformation into digital enterprises. The first path is the heritage trail – with “legacy” technology forming the background. Here, extant technologies are transformed by core IT teams to provide more API-driven approaches. Legacy systems can restrict companies that are transitioning into digital enterprises. To truly become a lead...
SYS-CON Events announced today that Daiya Industry will exhibit at the Japanese Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Ruby Development Inc. builds new services in short period of time and provides a continuous support of those services based on Ruby on Rails. For more information, please visit https://github.com/RubyDevInc.
As businesses evolve, they need technology that is simple to help them succeed today and flexible enough to help them build for tomorrow. Chrome is fit for the workplace of the future — providing a secure, consistent user experience across a range of devices that can be used anywhere. In her session at 21st Cloud Expo, Vidya Nagarajan, a Senior Product Manager at Google, will take a look at various options as to how ChromeOS can be leveraged to interact with people on the devices, and formats th...
SYS-CON Events announced today that Yuasa System will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Yuasa System is introducing a multi-purpose endurance testing system for flexible displays, OLED devices, flexible substrates, flat cables, and films in smartphones, wearables, automobiles, and healthcare.
SYS-CON Events announced today that Taica will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Taica manufacturers Alpha-GEL brand silicone components and materials, which maintain outstanding performance over a wide temperature range -40C to +200C. For more information, visit http://www.taica.co.jp/english/.
Organizations do not need a Big Data strategy; they need a business strategy that incorporates Big Data. Most organizations lack a road map for using Big Data to optimize key business processes, deliver a differentiated customer experience, or uncover new business opportunities. They do not understand what’s possible with respect to integrating Big Data into the business model.
Recently, REAN Cloud built a digital concierge for a North Carolina hospital that had observed that most patient call button questions were repetitive. In addition, the paper-based process used to measure patient health metrics was laborious, not in real-time and sometimes error-prone. In their session at 21st Cloud Expo, Sean Finnerty, Executive Director, Practice Lead, Health Care & Life Science at REAN Cloud, and Dr. S.P.T. Krishnan, Principal Architect at REAN Cloud, will discuss how they b...
Enterprises have taken advantage of IoT to achieve important revenue and cost advantages. What is less apparent is how incumbent enterprises operating at scale have, following success with IoT, built analytic, operations management and software development capabilities – ranging from autonomous vehicles to manageable robotics installations. They have embraced these capabilities as if they were Silicon Valley startups. As a result, many firms employ new business models that place enormous impor...
SYS-CON Events announced today that Dasher Technologies will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Dasher Technologies, Inc. ® is a premier IT solution provider that delivers expert technical resources along with trusted account executives to architect and deliver complete IT solutions and services to help our clients execute their goals, plans and objectives. Since 1999, we'v...
SYS-CON Events announced today that MIRAI Inc. will exhibit at the Japan External Trade Organization (JETRO) Pavilion at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. MIRAI Inc. are IT consultants from the public sector whose mission is to solve social issues by technology and innovation and to create a meaningful future for people.
SYS-CON Events announced today that TidalScale, a leading provider of systems and services, will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 - Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. TidalScale has been involved in shaping the computing landscape. They've designed, developed and deployed some of the most important and successful systems and services in the history of the computing industry - internet, Ethernet, operating s...
SYS-CON Events announced today that TidalScale will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. TidalScale is the leading provider of Software-Defined Servers that bring flexibility to modern data centers by right-sizing servers on the fly to fit any data set or workload. TidalScale’s award-winning inverse hypervisor technology combines multiple commodity servers (including their ass...
SYS-CON Events announced today that IBM has been named “Diamond Sponsor” of SYS-CON's 21st Cloud Expo, which will take place on October 31 through November 2nd 2017 at the Santa Clara Convention Center in Santa Clara, California.
Infoblox delivers Actionable Network Intelligence to enterprise, government, and service provider customers around the world. They are the industry leader in DNS, DHCP, and IP address management, the category known as DDI. We empower thousands of organizations to control and secure their networks from the core-enabling them to increase efficiency and visibility, improve customer service, and meet compliance requirements.