JSwat is a graphical Java debugger front-end, written for the Java 2 platform, utilizing the Java Platform Debugger Architecture (JPDA). The source code is licensed under the GNU General Public License. This program is under constant development, though it can be considered stable and mostly feature complete.
JSwat requires the Java 2
Standard Edition, version 1.4 or higher. Compatible software from
other vendors may be used, if so desired. The Java Platform Debugger
Architecture (JPDA) software, which is included in most releases of
the J2SE, is utilized by JSwat to carry out its debugging activities.
The required classes are typically found in the
<jdk>\lib\tools.jar file, and begin with the
prefix com.sun.jdi (where JDI stands for Java Debug
Interface).
JSwat includes a couple of additional jar files. They are referenced by the manifest of JSwat jar file and must be kept in the same directory as the JSwat jar file. The jar files do not have to be in your classpath, though it would not hurt if they were.
JSwat, like most Java debuggers, requires that the classes to be debugged be compiled using the -g flag. In addition, do not compile the classes with the optimization flags, as that may hinder debugging.
There are several ways to start JSwat, but we will only cover the simplest of these for now.
java -Djava.ext.dirs=<JAVA_HOME>\lib -jar <JSWAT_HOME>\jswat.jar
Unix users must replace \ with / in the line above.
Mac OS X users can leave out the -D option entirely.
Note that JAVA_HOME is the path to the JDK, while
JSWAT_HOME is the path to the jswat.jar
file. The <JAVA_HOME>\lib directory must contain
the tools.jar file in order for JSwat to start. This
file contains the JPDA classes (com.sun.jdi) used by
JSwat. If the file containing these classes is located elsewhere in
your system, you must make the appropriate change to the command used
to invoke JSwat.
JSwat can accept a string of commands to be executed as soon as it has completed its startup. These commands are passed at the end of the command line used to start the program. Here are some examples:
Read the help section titled "Commands" to learn more about using JSwat commands. Note that the last example uses slashes to escape the quotes used on the command line. See the appropriate documentation for your command shell to learn more.
java -Xbootclasspath/a:<JAVA_HOME>\lib\tools.jar -jar <JSWAT_HOME>\jswat.jar
tools.jar file and the JSwat jar files in your
classpath and invoke the program with this simple command:
java com.bluemarsh.jswat.Main
tools.jar file to the
<JAVA_HOME>\jre\lib\ext directory, then
starting JSwat like so:
java -jar <JSWAT_HOME>\jswat.jar
Note that the -jar option causes the classpath
setting to be ignored. This includes the path following the
-cp or -classpath options, as well as the
CLASSPATH environment variable.
The JSwat documentation is made up primarily of the built-in help. Help on JSwat commands is accessed using the "help" command. General help topics are available from the "Help" menu in JSwat. Additionally, there are several "how to" documents and a tutorial on the web site.
The correct way to exit JSwat is with either the window close button, the exit command, or the Exit item in the File menu. Using Ctrl-c to exit JSwat will likely cause problems and should be avoided. It must only be used in cases where the JVM hosting JSwat has frozen.
Removing JSwat from your system is generally pretty simple. Find the files, wherever it is that you originally put them, and delete them. If, on the other hand, you used one of the packaged versions such as RPM or DEB, you will need to remove the package using the appropriate tool.
To remove all traces of JSwat from your system, you will need to
look in only one place. If you are using Windows, look in the Windows
registry under the
HKEY_CURRENT_USER\Software\JavaSoft\Prefs\com\bluemarsh\jswat
key. Users of Unix-like systems will find the JSwat settings stored
in the ~/.java/.userPrefs/com/bluemarsh/jswat/
directory. You may also have created a jswat.init file,
so be sure to look for that as well.
The latest source code can be found in the Subversion repository
at http://www.bluemarsh.com/repos/jswat/trunk using any
web browser, or a Subversion client. See the
contributing
page on the JSwat web page for more information about using
Subversion to access the repository.
Below are notes concerning particular platforms and what must be done to make JSwat work correctly on them.
I am using OS X 10.3 with JDK 1.4.1 and I have had no problems launching JSwat and using it to debug Java applications. However, other users have had different experiences, which might be of interest to you.
David Cok discovered that the font height is reported as being one pixel too short in JDK 1.3. This causes several problems with the JSwat source viewer. David has provided a patch against the JSwat 1.6 source code that addresses the problem. David also reports that on OS X 10.1.5 he was unable to launch the debuggee from JSwat, although he could remotely attach to a running debuggee. But as he points out, this is true for all of the Java debuggers he tested on this platform.
Marc Hadley, using OS X 10.1.5, says it was necessary for him to
add the hostname of his machine to the netinfo file.
Otherwise he got an error about gethostbyname when
launching the debuggee from within JSwat.
The JRE, often installed with the JDK, seems to cause more
problems than it solves. If JSwat tells you that the JPDA cannot be
found and you are certain you followed the instructions above
correctly, then chances are the JRE is getting in the way. I
recommend saving yourself time and trouble and remove the JRE from
your system. If you cannot do this, then at least delete or rename
the java.exe and javaw.exe files in the
Windows directory.
There seems to be a problem with using JDK 1.4 on Windows NT 4.0,
relating to the DirectX features. The errors occur in the method
sun.awt.windows.Win32DDRenderer.doFillRectDD. The
solution appears to be quite simple, just add the following option
after java when starting JSwat:
-Dsun.java2d.noddraw=true
There seems to be a problem with using JDK 1.4.1 on Windows 2000 and XP relating to certain video cards. Basically, when the Java application exits, the operating system hangs. The relevant bug report is on the developer services site, which you may want to read for further information. There is a work-around that seems to work for some users and is worth trying. Add the following option after java when starting JSwat: -Dsun.java2d.d3d=false
A problem related to the one described above is that the JSwat application seems to hang on startup. Try installing the DirectX support in your system to avoid the issue. If that does not work, try the option mentioned above, or replace your video card per the bug report mentioned above.
Below are problems you might run into while using JSwat. Each offers a solution for either resolving or working around the issue.
See instructions above and be sure to follow them carefully. Check for any relevant information in the "Platform Particulars" section.
See the "Preferences Do Not Persist" item.
See the "Preferences Do Not Persist" item.
If the preferences in JSwat are not persisting, you may see one of the following symptoms:
java.util.prefs.BackingStoreException occurs,
maybe mentioning something about an XML parser, such as
xerces.The cause of the problem seems to be that an alternate XML parser is in the classpath. This XML parser does not understand how to handle the JavaSoft Preferences DTD and thus fails to read or write the Preferences data.
The solution is to run JSwat using the -jar option to provide a clean environment in which to run JSwat.
Simon Hill pointed out that the 2.1 version of the xerces parser no longer has the problem described above. If you are using an older version of this parser, you may want to upgrade.