Click here to close now.



Welcome!

Java IoT Authors: Bob Gourley, Dana Gardner, Scott Allen, Pat Romanski, AppDynamics Blog

Related Topics: Java IoT

Java IoT: Article

Parsing Command Line Arguments with Java

Parsing Command Line Arguments with Java

One of Java's great appeals is that the language provides out-of-the-box GUI development capabilities. Still, a lot of us use Java to write command line tools. Such tools are great to automate batch and offline processes. This article presents a framework that jump-starts the development of such tools.

Command line tools are usually invoked from a shell (e.g., DOS prompt, sh, ksh, etc.) and perform a certain task. The task can be customized based on the command line arguments. For instance:

telnet foo.bar.com

attempts to open a telnet connection to host foo.bar.com. It uses the default telnet port. The next example:

telnet -p 3434 foo.bar.com

attempts a similar connection using port 3434.

Command line tools can be as simple or as complicated as the developer desires. An example of a simple command line tool is the echo command found in most shells. On the other hand, the Java compiler and the Java Virtual Machine (JVM) are complex command line tools.

Java presents the command line arguments in an array of strings. This is already a huge improvement over C and C++, in which the arguments are presented as an array of C strings, i.e., an array of pointers to arrays of characters. Yet it comes short of the developer's desire to get the arguments parsed and ready to use.

Since I published my 1997 C++ command line parsing framework (see Reference), many readers have e-mailed me with requests and suggestions. The top two requests have been for a Java implementation and an improvement to handle arrays of arguments. In this article I present a total rewrite of the framework with improvements for Java programmers.

Using the Framework
Before moving to the implementation I'll demonstrate how to use the framework to write a command line utility. Let's say you want to write a utility called "mycat" - like the UNIX cat - which takes a number of files and concatenates them together into a larger file. A -v option turns verbose output on and off. A -l option allows the insertion of extra empty lines between the files. The command would look like:

&127;mycat [-l ] [-v] file1 file2 ... .

In your Main class you need to add a Token object for each argument. In this example we have three Tokens: the number of lines, the verbosity mode and the input files. In addition, you need to add an ApplicationSettings object. This object is used to contain all the arguments.

The source code for these settings is shown in Listing 1. I first declare the sm_main variable and then the three Token variables: sm_verbose, sm_files, sm_lines. The arguments in the constructor of each token object fully describe the expected usage of the Token:

  • Is it a switch or an argument?
  • What is the switch's name (e.g., -v)?
  • What is its type (integer, string, etc.)?
  • Can it appear multiple times (e.g., -l, 1, -l, 2)?
  • Is it a required argument?
  • If not, when the argument is missing:
    1. Is there an environment variable to provide the value?
    2. Is there a default value?

    A static initializer adds the Token variables to the ApplicationSettings variable. By the time the main() function of your application is reached, the ApplicationSettings object knows everything about the syntax of your command line utility.

    Listing 2 shows the main program of my example. The first line after the try statement calls the parseArgs() method of the ApplicationSettings object. The actual command line arguments are passed as an argument to the object. When the syntax is incorrect, a usage message is printed and an exception is thrown. Otherwise, the Token objects are set to contain appropriate values. For instance, when the -v option is present, the sm_verbose object will be set. Later, when its getValue() method is called, it will return true.

    In a similar fashion, if two files are passed as arguments, let's say foo.cc and bar.cc, the sm_files Token will be set appropriately. Its getValue(0) method will return foo.cc, its getValue(1) method will return bar.cc.

    Now compile the example with your favorite development environment and run the resulting code without passing any arguments. You should get the usage message in Listing 3. But wait a minute: you never wrote code to print usage messages; what's going on here? It's very simple. The framework uses the same code that defines the expected Tokens to generate usage statements. Kiss the ugly, always-out-of-date, static String statements that describe the usage of the utility goodbye.

    Now let's run the program again with some decent arguments. Let's say we run it with arguments "-v foo.cc bar.cc". The program prints the arguments correctly. Though we didn't pass any value for the -l switch, the Token returns 0. This is the expected behavior because the default value of the sm_lines Token is indeed 0.

    Why Use the Framework?
    By now some of the advantages of the framework should be obvious to you. The error-prone while and switch statements that usually parse the arguments have been replaced by a few very readable statements.

    These statements:

  • Document the usage of the command line utility
  • Encapsulate the settings so they can be used by the rest of the program
  • Automatically generate usage messages when the user enters incorrect syntax:
    1. Missing arguments
    2. Unexpected arguments
    3. Wrong types of arguments

    The stated advantages speed up the original development of any command line utility. They allow the developer to jump to the real code as soon as possible. At the same time, they provide immediate access to the command line settings and usage messages.

    Where the framework really shines is in the area where most of a developer's time is spent: software maintenance. If a command line utility is successful, users will ask for changes and improvements. Many of them will translate to more command line options or change the syntax of existing ones. The framework makes adding and modifying options trivial and safe. Compile-time messages will save the developer from runtime embarrassment.

    Finally, the framework is extensible. One can define new types of switches that accommodate new data types or anything else a developer desires.

    At this point you can go ahead, download the code and start using it in your own applications. The next few sections discuss the design of the framework.

    The StringArrayIterator Class
    The StringArrayIterator class is a utility class (see Listing 4). It encapsulates an array of strings and a position inside the array. The get() method returns the String at the current position. The moveNext() operation on the array allows the programmer to advance the current position to the next string. The EOF() operation determines when the end of the array has been reached.

    The ApplicationSettings object contains a StringArrayIterator object. It gets initialized from the command line arguments.

    The Token Class
    The Token class, shown in Listing 5, is an abstract class. Each Token object contains a description of an argument or a switch. After a successful parsing it also contains the value or values that were provided for the argument in the command line.

    During the parsing phase, the most important methods of the Token class are the parseSwitch() and parseArgument() methods. Both of them take the StringArrayIterator object with the command line arguments as input. If the current command line argument is recognized, three things occur: it's parsed, the pointer of the StringArrayIterator object is moved and a value of true is returned. If it's not recognized, a value of false is returned.

    The values that correspond to this switch or argument are stored in a Vector of objects. Subclasses determine their class. For instance, the StringToken subclass will have String objects, and the IntegerToken subclass will contain Integer objects.

    While the program is running, the values are accessible using the getValue(int) and getValue() operations.

    Token Subclasses
    A Token subclass encapsulates arguments of a specific type. For example, there's a StringToken, an IntegerToken, etc. Since most of its methods have a generic implementation, each Token subclass has very few methods to implement.

    Listing 6 presents the implementation for the class StringToken. A few more subclasses are provided in the downloaded code. You can extend the framework by implementing more subclasses.

    The ApplicationSettings Object
    The ApplicationSettings object puts everything I've discussed so far together (see Listing 7). It contains all the Token objects and initiates the parsing algorithm. The user triggers the parsing by calling the parseArgs() method.

    The command line arguments are assigned to the StringArrayIterator member of the class. Then, for every command line argument, each Token object is called and asked to parse it as either an option or an argument.

    If no Token object can parse the argument, a usage message is printed by iterating through the Tokens and calling their printUsage() and printUsageExtended() methods. Both methods take an OutputStream as an argument. They print their output to this stream.

    Pure Java and Impurities
    Almost all the code is pure Java. Since pure Java doesn't provide support for environment variables and assertions, I had to use the functions provided in my environment, the Win32 Virtual Machine.

    These few lines of code are carefully isolated in the util.java file shown in Listing 8. In a pure Java environment you can comment out three lines of code from this file. You don't get assertions and support for initialization of arguments from environment variables. Otherwise, everything else works as advertised.

    Limitations
    The framework doesn't provide support for complex scenarios. For instance, there's no support for switches that depend on each other. You can't dictate that the -t option can appear if and only if the -p option appears. You'd have to implement such checks yourself after the arguments were parsed.

    Conclusion
    In this article I presented an extensible Java framework. The framework simplifies the development and maintenance of code that parses the arguments of command line utilities and tools.

    The framework doesn't provide support for complex scenarios. Still, my experience is that the framework covers most common cases. I expect that it will be as useful for Java development as it has been for C++.

    Reference
    P. Kougiouris (1997). "Yet Another Command-Line Parser." C/C++ Users Journal, Vol. 15, No. 4, April.

  • More Stories By Panos Kougiouris

    Panos Kougiouris has ten years' experience in software development for high-tech companies. For the past three years he has been at Healtheon, a Silicon Valley startup, and he has held technical positions with Oracle and Sun Microsystems. Panos holds computer science degrees from the University of Illinois at Urbana-Champaign and the University of Patra, Greece.

    Comments (1) View Comments

    Share your thoughts on this story.

    Add your comment
    You must be signed in to add a comment. Sign-in | Register

    In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


    Most Recent Comments
    AST 12/04/04 10:52:06 AM EST

    Hi. Just wanted to point out another package for solving this problem. It supports popt-style autohelp as well as POSIX options, joined options (-Wall -Dfoo=bar), repeated options and of course GNU-style (--some-long-option) options.

    Where the library really differs is that it leverages the GoF Command Pattern to make the options "active" in a similar manner to the Swing Action objects. Another feature is the ability to specify which sets of options must be present or cannot be present without requiring coding this logic yourself. The parser does the work for you.

    An article discussing how this can be done at http://te-code.sourceforge.net/article-20041121-cli.html .

    Ok, and yes, I'm a bit biased because I wrote the library... ;)

    Hope this helps,

    ast

    @ThingsExpo Stories
    With an estimated 50 billion devices connected to the Internet by 2020, several industries will begin to expand their capabilities for retaining end point data at the edge to better utilize the range of data types and sheer volume of M2M data generated by the Internet of Things. In his session at @ThingsExpo, Don DeLoach, CEO and President of Infobright, will discuss the infrastructures businesses will need to implement to handle this explosion of data by providing specific use cases for filte...
    SYS-CON Events announced today that Fusion, a leading provider of cloud services, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Fusion, a leading provider of integrated cloud solutions to small, medium and large businesses, is the industry's single source for the cloud. Fusion's advanced, proprietary cloud service platform enables the integration of leading edge solutions in the cloud, including clou...
    SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management...
    SYS-CON Events announced today that Alert Logic, Inc., the leading provider of Security-as-a-Service solutions for the cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Alert Logic, Inc., provides Security-as-a-Service for on-premises, cloud, and hybrid infrastructures, delivering deep security insight and continuous protection for customers at a lower cost than traditional security solutions. Ful...
    The cloud promises new levels of agility and cost-savings for Big Data, data warehousing and analytics. But it’s challenging to understand all the options – from IaaS and PaaS to newer services like HaaS (Hadoop as a Service) and BDaaS (Big Data as a Service). In her session at @BigDataExpo at @ThingsExpo, Hannah Smalltree, a director at Cazena, will provide an educational overview of emerging “as-a-service” options for Big Data in the cloud. This is critical background for IT and data profes...
    SYS-CON Events announced today that VAI, a leading ERP software provider, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. VAI (Vormittag Associates, Inc.) is a leading independent mid-market ERP software developer renowned for its flexible solutions and ability to automate critical business functions for the distribution, manufacturing, specialty retail and service sectors. An IBM Premier Business Part...
    Fortunately, meaningful and tangible business cases for IoT are plentiful in a broad array of industries and vertical markets. These range from simple warranty cost reduction for capital intensive assets, to minimizing downtime for vital business tools, to creating feedback loops improving product design, to improving and enhancing enterprise customer experiences. All of these business cases, which will be briefly explored in this session, hinge on cost effectively extracting relevant data from ...
    As enterprises work to take advantage of Big Data technologies, they frequently become distracted by product-level decisions. In most new Big Data builds this approach is completely counter-productive: it presupposes tools that may not be a fit for development teams, forces IT to take on the burden of evaluating and maintaining unfamiliar technology, and represents a major up-front expense. In his session at @BigDataExpo at @ThingsExpo, Andrew Warfield, CTO and Co-Founder of Coho Data, will dis...
    With the Apple Watch making its way onto wrists all over the world, it’s only a matter of time before it becomes a staple in the workplace. In fact, Forrester reported that 68 percent of technology and business decision-makers characterize wearables as a top priority for 2015. Recognizing their business value early on, FinancialForce.com was the first to bring ERP to wearables, helping streamline communication across front and back office functions. In his session at @ThingsExpo, Kevin Roberts...
    SYS-CON Events announced today that Interoute, owner-operator of one of Europe's largest networks and a global cloud services platform, has been named “Bronze Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2015 at the Javits Center in New York, New York. Interoute is the owner-operator of one of Europe's largest networks and a global cloud services platform which encompasses 12 data centers, 14 virtual data centers and 31 colocation centers, with connections to 195 ad...
    Most people haven’t heard the word, “gamification,” even though they probably, and perhaps unwittingly, participate in it every day. Gamification is “the process of adding games or game-like elements to something (as a task) so as to encourage participation.” Further, gamification is about bringing game mechanics – rules, constructs, processes, and methods – into the real world in an effort to engage people. In his session at @ThingsExpo, Robert Endo, owner and engagement manager of Intrepid D...
    Eighty percent of a data scientist’s time is spent gathering and cleaning up data, and 80% of all data is unstructured and almost never analyzed. Cognitive computing, in combination with Big Data, is changing the equation by creating data reservoirs and using natural language processing to enable analysis of unstructured data sources. This is impacting every aspect of the analytics profession from how data is mined (and by whom) to how it is delivered. This is not some futuristic vision: it's ha...
    WebRTC has had a real tough three or four years, and so have those working with it. Only a few short years ago, the development world were excited about WebRTC and proclaiming how awesome it was. You might have played with the technology a couple of years ago, only to find the extra infrastructure requirements were painful to implement and poorly documented. This probably left a bitter taste in your mouth, especially when things went wrong.
    Learn how IoT, cloud, social networks and last but not least, humans, can be integrated into a seamless integration of cooperative organisms both cybernetic and biological. This has been enabled by recent advances in IoT device capabilities, messaging frameworks, presence and collaboration services, where devices can share information and make independent and human assisted decisions based upon social status from other entities. In his session at @ThingsExpo, Michael Heydt, founder of Seamless...
    The IoT's basic concept of collecting data from as many sources possible to drive better decision making, create process innovation and realize additional revenue has been in use at large enterprises with deep pockets for decades. So what has changed? In his session at @ThingsExpo, Prasanna Sivaramakrishnan, Solutions Architect at Red Hat, discussed the impact commodity hardware, ubiquitous connectivity, and innovations in open source software are having on the connected universe of people, thi...
    WebRTC: together these advances have created a perfect storm of technologies that are disrupting and transforming classic communications models and ecosystems. In his session at WebRTC Summit, Cary Bran, VP of Innovation and New Ventures at Plantronics and PLT Labs, provided an overview of this technological shift, including associated business and consumer communications impacts, and opportunities it may enable, complement or entirely transform.
    There are so many tools and techniques for data analytics that even for a data scientist the choices, possible systems, and even the types of data can be daunting. In his session at @ThingsExpo, Chris Harrold, Global CTO for Big Data Solutions for EMC Corporation, showed how to perform a simple, but meaningful analysis of social sentiment data using freely available tools that take only minutes to download and install. Participants received the download information, scripts, and complete end-t...
    For manufacturers, the Internet of Things (IoT) represents a jumping-off point for innovation, jobs, and revenue creation. But to adequately seize the opportunity, manufacturers must design devices that are interconnected, can continually sense their environment and process huge amounts of data. As a first step, manufacturers must embrace a new product development ecosystem in order to support these products.
    Manufacturing connected IoT versions of traditional products requires more than multiple deep technology skills. It also requires a shift in mindset, to realize that connected, sensor-enabled “things” act more like services than what we usually think of as products. In his session at @ThingsExpo, David Friedman, CEO and co-founder of Ayla Networks, discussed how when sensors start generating detailed real-world data about products and how they’re being used, smart manufacturers can use the dat...
    When it comes to IoT in the enterprise, namely the commercial building and hospitality markets, a benefit not getting the attention it deserves is energy efficiency, and IoT’s direct impact on a cleaner, greener environment when installed in smart buildings. Until now clean technology was offered piecemeal and led with point solutions that require significant systems integration to orchestrate and deploy. There didn't exist a 'top down' approach that can manage and monitor the way a Smart Buildi...