The Java Developer's Kit
Java has taken the Internet and programming communities by storm during the past year with its promise to enable the creation of software that can run on any platform from a single binary file and be used securely in a distributed network environment.
The Java concept is simple: a single source code file is compiled to a single pseudo-binary file containing Java byte codes. This binary file can be run on any platform for which a Java interpreter or other runtime engine exists.
In order to develop and test these Java applications, it is necessary to have access to several critical development tools, including a compiler, a debugger and a Java interpreter for testing applications. Numerous Java development environments already exist—primarily for MS-Windows systems. These full professional development tools are produced by the likes of Borland and Symantec. For Linux, and Unix in general, this type of commercial development tool hasn't become available.
Nonetheless, this doesn't mean that Linux users are unable to develop Java applets and applications. Sun Microsystems has developed a free Java Developer's Kit (JDK) which includes a compiler, a debugger, a runtime environment and an applet viewer for testing Java applets embedded in web pages.
The Java Developer's Kit was originally developed by Sun for SPARC, Solaris and Windows NT/95. These versions of the kit, along with more recent versions for x86 Solaris and MacOS, are available from the JavaSoft web site at http://www.javasoft.com/
Sun has also allowed other organizations to port the JDK to other platforms. The Blackdown Organization (Randy Chapman) has ported version 1.0.1 of the JDK to Linux and makes binaries available for x86 versions of Linux. The JDK distribution for Linux is available from ftp://ftp.blackdown.org/pub/Java/linux/. Blackdown also has a web page at www.blackdown.org/. On the web site you will find three files:
linux.jdk-1.0.1-try3.common.tar.gz linux.jdk-1.0.1-try3.static-motif-bin.tar.gz linux.jdk-1.0.1-try3.shared-motif-bin.tar.gz
It is necessary to download two of these three files:
The last file requires an ELF binary of version 2.0 of the Motif libraries (libXm.so.2). If you don't have Motif, download linux.jdk-1.0.1-try3.static-motif-bin.tar.gz instead—it is a larger file but will work regardless of whether you have the Motif libraries or not. Throughout this article we will be using linux.jdk-1.0.1-try3.static-motif-bin.tar.gz.
All versions of the Java Developer's Kit also require the following libraries, many of which may already be on your system:
If you are missing any of these libraries, the JDK will not work. These libraries are all freely available on the Internet.
Once the “common” tar file and one of the Motif tars have been downloaded, they need to be uncompressed. The documentation with the Linux JDK recommends installing the JDK in the /usr/local directory (although it can be installed elsewhere). To do this, copy the two compressed tar files to /usr/local with:
cp linux.jdk-1.0.1-try3.common.tar.gz /usr/local cp linux.jdk-1.0.1-try3.static-motif-bin.taR.GZ /usr/local
Then, the files can be uncompressed and untarred with:
tar xzvf linux.jdk-1.0.1-try3.common.tar.gz linux.jdk-1.0.1-try3.static-motif-bin.tar.gz
This will create a directory java/ under /usr/local which contains four subdirectories: bin, demo, include and lib. /usr/local/java will also contain a zip file with the source and various README and HOWTO files. The bin/ directory contains the scripts used to execute all the components of the JDK. The components are:
appletviewer: A viewer to test applets embedded in HTML documents.
javac: The Java compiler: compiles Java source code to Java byte code binary files (known as class files). The class files produced by javac can be run by a Java interpreter on any platform.
java: The Java interpreter: used to execute Java class files under Linux.
jdb: The Java Debugger: a command-line debugger which is in alpha development.
Each of these scripts in java/bin actually call executable files in java/bin/i586. These scripts expect certain tools to exist in fixed locations in your system. Specifically, the appletviewer script expects mkdir to be in /usr/bin and pwd to be in /bin. On some systems, this may not be true (for instance, in RedHat-derived systems, you may find mkdir in /bin). There are two solutions to this problem. One is to edit java/bin/appletviewer and replace the incorrect occurrences of /usr/bin/mkdir or /bin/pwd with the correct full paths of these programs.
The second solution is to create symbolic links in the directories expected by appletviewer. For instance, on RedHat systems where mkdir is in /bin, a symbolic link could be created in /usr/bin with the command:
ln -s /bin/mkdir /usr/bin/mkdir
If you expect to be using the JDK components frequently, you will probably want to add the java/bin directory to your path. Assuming you installed the JDK under /usr/local and you are running the bash shell (the default shell for many Linux distributions), you could add the following lines to the .bashrc file in your home directory:
PATH=/usr/local/java/bin:$PATH export PATH
If you are running C shell, the following line at the end of your .cshrc file in your home directory will do the job:
setenv PATH /usr/local/java/bin:$PATH
Practical Task Scheduling Deployment
July 20, 2016 12:00 pm CDT
One of the best things about the UNIX environment (aside from being stable and efficient) is the vast array of software tools available to help you do your job. Traditionally, a UNIX tool does only one thing, but does that one thing very well. For example, grep is very easy to use and can search vast amounts of data quickly. The find tool can find a particular file or files based on all kinds of criteria. It's pretty easy to string these tools together to build even more powerful tools, such as a tool that finds all of the .log files in the /home directory and searches each one for a particular entry. This erector-set mentality allows UNIX system administrators to seem to always have the right tool for the job.
Cron traditionally has been considered another such a tool for job scheduling, but is it enough? This webinar considers that very question. The first part builds on a previous Geek Guide, Beyond Cron, and briefly describes how to know when it might be time to consider upgrading your job scheduling infrastructure. The second part presents an actual planning and implementation framework.
Join Linux Journal's Mike Diehl and Pat Cameron of Help Systems.
Free to Linux Journal readers.Register Now!
- SUSE LLC's SUSE Manager
- Murat Yener and Onur Dundar's Expert Android Studio (Wrox)
- My +1 Sword of Productivity
- Managing Linux Using Puppet
- Non-Linux FOSS: Caffeine!
- SuperTuxKart 0.9.2 Released
- Doing for User Space What We Did for Kernel Space
- Google's SwiftShader Released
- Parsing an RSS News Feed with a Bash Script
- Rogue Wave Software's Zend Server
With all the industry talk about the benefits of Linux on Power and all the performance advantages offered by its open architecture, you may be considering a move in that direction. If you are thinking about analytics, big data and cloud computing, you would be right to evaluate Power. The idea of using commodity x86 hardware and replacing it every three years is an outdated cost model. It doesn’t consider the total cost of ownership, and it doesn’t consider the advantage of real processing power, high-availability and multithreading like a demon.
This ebook takes a look at some of the practical applications of the Linux on Power platform and ways you might bring all the performance power of this open architecture to bear for your organization. There are no smoke and mirrors here—just hard, cold, empirical evidence provided by independent sources. I also consider some innovative ways Linux on Power will be used in the future.Get the Guide