Debugging Applications

3 Debugging Applications

This chapter gives guidelines for debugging applications in the Oracle GlassFish Server.

The following topics are addressed here:

Enabling Debugging
JPDA Options
Generating a Stack Trace for Debugging
Application Client Debugging
Open Message Queue Debugging
Enabling Verbose Mode
Class Loader Debugging
GlassFish Server Logging
Profiling Tools

Enabling Debugging

When you enable debugging, you enable both local and remote debugging. To start the server in debug mode, use the --debug option as follows:

asadmin start-domain --debug [domain-name]

You can then attach to the server from the Java Debugger (jdb) at its default Java Platform Debugger Architecture (JPDA) port, which is 9009. For example, for UNIX systems:

jdb -attach 9009

For Windows:

jdb -connect com.sun.jdi.SocketAttach:port=9009

For more information about the jdb debugger, see the following links:

Java Platform Debugger Architecture - The Java Debugger: http://java.sun.com/javase/technologies/core/toolsapis/jpda/
Java Platform Debugger Architecture - Connecting with JDB: http://java.sun.com/javase/technologies/core/toolsapis/jpda/

GlassFish Server debugging is based on the JPDA. For more information, see JPDA Options.

You can attach to the GlassFish Server using any JPDA compliant debugger, including that of NetBeans (http://www.netbeans.org), Java Studio Enterprise, JBuilder, Eclipse, and so on.

You can enable debugging even when the GlassFish Server is started without the --debug option. This is useful if you start the GlassFish Server from the Windows Start Menu, or if you want to make sure that debugging is always turned on.

To Set the Server to Automatically Start Up in Debug Mode

Use the Administration Console. Select the JVM Settings component under the relevant configuration.
Check the Debug Enabled box.
To specify a different port (from 9009, the default) to use when attaching the JVM software to a debugger, specify address= port-number in the Debug Options field.
To add JPDA options, add any desired JPDA debugging options in Debug Options. See JPDA Options.

JPDA Options

The default JPDA options in GlassFish Server are as follows:

-Xdebug -agentlib:transport=dt_socket,server=y,suspend=n,address=9009

For Windows, you can change dt_socket to dt_shmem.

If you substitute suspend=y, the JVM software starts in suspended mode and stays suspended until a debugger attaches to it. This is helpful if you want to start debugging as soon as the JVM software starts.

To specify a different port (from 9009, the default) to use when attaching the JVM software to a debugger, specify `address=`port-number.

You can include additional options. A list of JPDA debugging options is available at http://java.sun.com/javase/technologies/core/toolsapis/jpda/.

Generating a Stack Trace for Debugging

To generate a Java stack trace for debugging, use the asadmin generate-jvm-report --type=thread command. The stack trace goes to the domain-dir`/logs/server.log` file and also appears on the command prompt screen. For more information about the asadmin generate-jvm-report command, see the GlassFish Server Open Source Edition Reference Manual.

Application Client Debugging

When the appclient script executes the java command to run the Application Client Container (ACC), which in turn runs the client, it includes on the command line the value of the VMARGS environment variable. You can set this variable to any suitable value. For example:

VMARGS=-agentlib:transport=dt_socket,server=y,suspend=y,address=8118

For debugging an application client, you should set suspend to y so you can connect the debugger to the client before any code has actually executed. Otherwise, the client may start running and execute past the point you want to examine.

You should use different ports for the server and client if you are debugging both concurrently. For details about setting the port, see JPDA Options.

You can also include JVM options in the appclient script directly. For information about the appclient script, see the GlassFish Server Open Source Edition Reference Manual.

Note	The Application Client Container is supported only in the full GlassFish Server, not in the Web Profile. See Developing Java Clients.

Open Message Queue Debugging

Open Message Queue has a broker logger, which can be useful for debugging Java Message Service (JMS) applications, including message-driven bean applications. You can adjust the logger’s verbosity, and you can send the logger output to the broker’s console using the broker’s -tty option. For more information, see the Open Message Queue Administration Guide.

Note	JMS resources are supported only in the full GlassFish Server, not in the Web Profile. See Using the Java Message Service.

Enabling Verbose Mode

To have the server logs and messages printed to System.out on your command prompt screen, you can start the server in verbose mode. This makes it easy to do simple debugging using print statements, without having to view the server.log file every time.

To start the server in verbose mode, use the --verbose option as follows:

asadmin start-domain --verbose [domain-name]

When the server is in verbose mode, messages are logged to the console or terminal window in addition to the log file. In addition, pressing Ctrl-C stops the server and pressing Ctrl-\ (on UNIX platforms) or Ctrl-Break (on Windows platforms) prints a thread dump. On UNIX platforms, you can also print a thread dump using the jstack command (see http://docs.oracle.com/javase/8/docs/technotes/tools/share/jstack.html) or the command kill -QUIT process_id.

Class Loader Debugging

To generate class loading messages, use the following asadmin create-jvm-options command:

asadmin create-jvm-options -verbose\:class

To send the JVM messages to a special JVM log file instead of stdout, use the following asadmin create-jvm-options commands:

asadmin create-jvm-options -XX\:+LogVMOutput
asadmin create-jvm-options -XX\:LogFile=${com.sun.aas.instanceRoot}/logs/jvm.log

Note	These `-XX` options are specific to the OpenJDK (or Hotspot) JVM and do not work with the JRockit JVM.

To send the GlassFish Server messages to the Administration Console instead of stderr, start the domain in verbose mode as described in Enabling Verbose Mode.

GlassFish Server Logging

You can use the GlassFish Server’s log files to help debug your applications. Use the Administration Console. Select the Stand-Alone Instances component, select the instance from the table, then click the View Log Files button in the General Information page. Or select the Cluster component, select the cluster from the table, select the Instances tab, select the instance from the table, then click the View Log Files button in the General Information page.

To change logging settings, select Logger Settings under the relevant configuration.

For details about logging, click the Help button in the Administration Console.

Profiling Tools

You can use a profiler to perform remote profiling on the GlassFish Server to discover bottlenecks in server-side performance. This section describes how to configure profilers for use with GlassFish Server.

The following topics are addressed here:

The NetBeans Profiler
The HPROF Profiler
The JProbe Profiler

Information about comprehensive monitoring and management support in the Java 2 Platform, Standard Edition ( J2SE platform) is available at http://docs.oracle.com/javase/8/docs/technotes/guides/management/index.html.

The NetBeans Profiler

For information on how to use the NetBeans profiler, see http://profiler.netbeans.org/index.html.

The HPROF Profiler

The Heap and CPU Profiling Agent (HPROF) is a simple profiler agent shipped with the Java 2 SDK. It is a dynamically linked library that interacts with the Java Virtual Machine Profiler Interface (JVMPI) and writes out profiling information either to a file or to a socket in ASCII or binary format.

HPROF can monitor CPU usage, heap allocation statistics, and contention profiles. In addition, it can also report complete heap dumps and states of all the monitors and threads in the Java virtual machine. For more details on the HPROF profiler, see the technical article at http://java.sun.com/developer/technicalArticles/Programming/HPROF.html.

After HPROF is enabled using the following instructions, its libraries are loaded into the server process.

To Use HPROF Profiling on UNIX

Use the Administration Console. Select the JVM Settings component under the relevant configuration. Then select the Profiler tab.
Edit the following fields:
- Profiler Name - hprof
- Profiler Enabled - true
- Classpath - (leave blank)
- Native Library Path - (leave blank)
- JVM Option - Select Add, type the HPROF JVM option in the Value field, then check its box. The syntax of the HPROF JVM option is as follows:

-Xrunhprof[:help]|[:param=value,param2=value2, ...]

Here is an example of params you can use:

-Xrunhprof:file=log.txt,thread=y,depth=3

The file parameter determines where the stack dump is written.
Using help lists parameters that can be passed to HPROF. The output is as follows:

Hprof usage: -Xrunhprof[:help]|[:<option>=<value>, ...]

Option Name and Value   Description             Default
---------------------   -----------             -------
heap=dump|sites|all     heap profiling          all
cpu=samples|old         CPU usage               off
format=a|b              ascii or binary output  a
file=<file>             write data to file      java.hprof
                               (.txt for ascii)
net=<host>:<port>       send data over a socket write to file
depth=<size>            stack trace depth       4
cutoff=<value>          output cutoff point     0.0001
lineno=y|n              line number in traces?  y
thread=y|n              thread in traces?       n
doe=y|n                 dump on exit?           y

Note	Do not use help in the JVM Option field. This parameter prints text to the standard output and then exits. The help output refers to the parameters as options, but they are not the same thing as JVM options.

Restart the GlassFish Server.
This writes an HPROF stack dump to the file you specified using the file HPROF parameter.

The JProbe Profiler

Information about JProbe from Sitraka is available at http://www.quest.com/jprobe/.

After JProbe is installed using the following instructions, its libraries are loaded into the server process.

To Enable Remote Profiling With JProbe

Install JProbe 3.0.1.1.
For details, see the JProbe documentation.
Configure GlassFish Server using the Administration Console:
Select the JVM Settings component under the relevant configuration. Then select the Profiler tab.
Edit the following fields before selecting Save and restarting the server:
Profiler Name - jprobe
Profiler Enabled - true
Classpath - (leave blank)
Native Library Path - JProbe-dir`/profiler`
JVM Option - For each of these options, select Add, type the option in the Value field, then check its box:

    -Xbootclasspath/p:JProbe-dir/profiler/jpagent.jar
    -Xrunjprobeagent
    -Xnoclassgc

Note	If any of the configuration options are missing or incorrect, the profiler might experience problems that affect the performance of the GlassFish Server.

When the server starts up with this configuration, you can attach the profiler. 3. Set the following environment variable:

JPROBE_ARGS_0=-jp_input=JPL-file-path

See Step 6 for instructions on how to create the JPL file. 4. Start the server instance. 5. Launch the jpprofiler and attach to Remote Session. The default port is 4444. 6.
Create the JPL file using the JProbe Launch Pad. Here are the required settings: 1. Select Server Side for the type of application. 2. On the Program tab, provide the following details:
Target Server - other-server
Server home Directory - as-install
Server class File - com.sun.enterprise.server.J2EERunner
Working Directory - as-install
Classpath - as-install`/lib/appserv-rt.jar`
Source File Path - source-code-dir (in case you want to get the line level details)
Server class arguments - (optional)
Main Package - com.sun.enterprise.server
You must also set VM, Attach, and Coverage tabs appropriately. For further details, see the JProbe documentation. After you have created the JPL file, use this an input to JPROBE_ARGS_0.