Displaying a Java Stack Trace

When debugging your Java applications, you may want to display a stack trace. If you launched your application from the command line, CTRL-\ generates a SIGQUIT signal and prints the current stack trace in your Terminal window. If you launch your Java application from the Finder, you just need to find its process ID (PID) and deliver a SIGQUIT signal to that process. You see the stack trace in the Console application. For example, first launch Applet Launcher, Terminal, and Console (all are in Applications/Utilities). If you want to generate a stack trace for Applet Launcher, in Terminal type:

ps -auxwww | grep "Applet Launcher"

You would see the results as something like:

bgerfen 1490   0.0  2.3   255700  17912  ??  S     2:39PM   0:05.76 /Applications/Utilities/Java/Applet Launcher.app/Contents/MacOS/Applet Launcher -psn_0_5898241

bgerfen 1507   0.0  0.0     1116      4 std  R+    2:41PM   0:00.00 grep -i Applet Launcher

Once you have the appropriate PID, kill it. For this example this looks like:

kill -QUIT 1490

Console displays the stack trace.

You may also want to include monitor status information in the stack trace. If you are running your application from the command line, just run your program with the -XX:+JavaMonitorsInStackTrace flag. You can also make a .hotspotrc file in your home directory with this line in it:

+JavaMonitorsInStackTrace

Since this file is parsed every time a Java VM starts up, it is in effect for applications run from the command line, double-clickable applications run from the Finder, and even Java applications embedded within other applications.

If you have a reproducible crash, you might also want to find the stack trace for the native code by running your application in gdb. After a crash use this command:

thread apply all bt

Project Builder

Project Builder is a complete integrated developmente environment (IDE) that allows you to edit, compile, debug, and package your Java applications. A tutorial of how to build a simple Java application is included in Project Builder Tutorial. Additional details of using Project Builder to build Java applications are included in the section on compiling Java files in Project Builder Help.

MRJAppBuilder

MRJAppBuilder is a utility for packaging already-compiled Java applications to run as Mac OS X applications. MRJAppBuilder constructs applications in the same application bundle format as other Mac OS X applications. It is very simple to use and allows you, with minimal work, to make your Java application launch like native Mac OS X applications. You can even easily set options like the Dock icon and the application name that appears in the menu bar without modifying your Java source code. Additionally you can use MRJAppBuilder to set runtime flags that you might want to use only in Mac OS X. In order to use MRJAppBuilder, you need only know the main class name of your application and have access to the .class files.

The interface to MRJAppBuilder is simple and readily apparent when you open the application. As illustrated in Figure 4-1, there are four tabbed panes in the MRJAppBuilder window.

The information in the Application pane is all that you need to make a Mac OS X application. All three fields are required. The “Main classname” field is where you enter the name of the class that contains main. This field represents the value of the property com.apple.mrj.application.main. Remember to include a full package name. For example, com.myCompany.myMainClass.

The Classpath field allows you to modify the classpath. This is automatically set to point to the JAR file that you’re bundling into your application. If you want to use JAR or .class files that will not be included in the resulting application bundle, add a classpath entry of this form:

$APP_PACKAGE/../MyJARFile.jar

$APP_PACKAGE is a special path string that represents the application bundle directory. The last required field is the “Output file” field. This is where the resulting application bundle will be built. An optional setting in this pane is the application icon. Click the icon in the “Output file” section to bring up a file chooser dialog for selecting an .icns file.

Settings in Mac OS X, Java Properties, and Merge Files panes are optional. The Mac OS X pane allows you to set values specific to the Mac OS X application bundle format. If you do not specify CFBundleExecutable or CFBundleName, they are set based on the name of the output file you choose.

The Java Properties pane lets you set specific runtime properties, which can include standard Java properties as well as the specific Mac OS X system properties discussed in Mac OS X Application Properties. See Setting Runtime Properties in MRJAppBuilder for more information on the Java Properties pane.

The Merge Files pane provides a means for adding files to the application bundle, such as .zip or JAR files. Each item added to the merge list is copied into the application’s Contents/Resources/Java directory. Each item you add to the merge list gets automatically added to the classpath.

When you have finished making settings, click Build Application. MRJAppBuilder does not provide an import mechanism. If you build an application and want to change certain settings, you need to make a new application with MRJAppBuilder or modify the Info.plist and MRJApp.properties files by hand. Information on these files can be found in Application Bundles.

Applet Launcher

Applet Launcher (in /Applications/Utilities/Java) allows you to run applets without the overhead of launching a Web browser. It provides a graphical interface to Sun’s Java Plug-in. If you want to test the performance of your applet with the sun.applet.AppletViewer class, you should use the appletviewer command-line tool (/usr/bin/). You can enter the path to an applet using its fully-qualified URL, and then press the Launch button. For example, entering the following URL launches the ArcTest applet:

file:///Developer/Examples/Java/Applets/ArcTest/example1.html

Performance and behavior settings for applets may be adjusted in the Java Plugin Settings application installed in /Applications/Utilities/Java.

Other Tools

The Mac OS X Developer Tools also provide many tools useful for any kind of development, not just Java. For example Package Maker, File Merge, and Icon Composer are just a few examples. Figure 4-2 shows all of the tools that get installed into /Developer/Applications.

In addition to the Apple-supplied tools, since you have both a UNIX foundation and a full implementation of Java 2 Standard Edition, you may use many third party tools in Mac OS X. IDEs like Borland’s JBuilder, Sun’s ONE Studio, and Metrowerks’ CodeWarrior are all available. There are many text editors, as well as other tools for specific functionality like ant, JUnit, and OptimizeIt. If you are interested in Java 2 Platform, Enterprise Edition (J2EE) development, Pramati and Jboss both offer J2EE development environments for Mac OS X. Some of the most important pieces of J2EE, like Enterprise Java Beans and Java Server Pages (JSP), are supported in Apple’s WebObjects product (http://www.apple.com/webobjects). Zentek’s iJADE product line is one solution for Java 2 Platform, Micro Edition (J2ME) development in Mac OS X.