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Explain how to perform debugging when something doesn't work in Cargo

. Indeed it can happen that the container does not start or stop as expected. Or that some deployable does not deploy fine. Or whatever else! Here is a short list of things you can do to try debugging the problem.

Enabling the Java debugger

Most Java Virtual Machine implementations support remote debugging. Once started in debug mode, you can then remotely connect to your container using any IDE and debug your container and/or application.

In order to do so, add the following arguments to the JVM arguments configuration:

Code Block


  • suspend is whether the launch of the container should first wait for a remote debugger to connect. If y, the container will wait for you to connect with your remote debugger before starting; if n the container will start immediately and at the same time listen on the remote debugging port.
  • port is the port number to use for remote debugging.

Here is an example for starting a JOnAS 5.x container in Remote Debug on port 8000 without suspend mode using the Maven2 plugin:

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Once the server is started, follow these steps to remotely debug your server and/or application:

  1. Click Debug - Attach Debugger...
  2. In the window that appears, type in the remote host name and the port number then click OK

Steps for achieving the same in Eclipse IDE are similar.

Redirecting container output to a file

The Container.setOutput(File) API allows you to redirect the container console (stdout) to a file. This is the first file you should check in case of problem.

Example using the Java API

Starting Tomcat 4.x specifying an output console log file:

Code Block
LocalContainer container = new Tomcat4xLocalContainer(
    new CatalinaStandaloneLocalConfiguration("target/tomcat4x"));



Use the container.setAppend(true|false) method to decide whether the log file is recreated or whether it is appended to, keeping the previous execution logs (by default, the file is recreated at every container start or stop).

Example using the Ant API

Starting Tomcat 4.x specifying an output console log file:

Code Block
<cargo containerId="tomcat4x" home="c:/apps/jakarta-tomcat-4.1.30" 

Use the append="true|false" attribute for controlling the log file creation behavior.

Generating Cargo logs

Some Cargo classes support generation of logs. This is implemented through the notion of Logger.

For example to turn on logging monitoring on a Container class, you can use:

Code Block
Logger fileLogger = new FileLogger(new File("c:/tmp/cargo.log"), true); 

There are several Loggers that are readily available in the Cargo distribution:

Turning on container logs

Cargo is able to configure containers to generate various levels logs. There are 3 levels defined in LoggingLevel.LOW, LoggingLevel.MEDIUM and LoggingLevel.HIGH (LoggingLevel.MEDIUM is the default value). They represent the quantity of information you wish to have in the generated log file. You can tune container logging by using the following API:

Code Block
configuration.setProperty(GeneralPropertySet.LOGGING, LoggingLevel.HIGH.getLevel());

The class has been introduced in CARGO 1.1.0. In previous versions of CARGO, use the string constants low, medium and high.

The generated log files will then be found in the working directory you have specified on the container (through the container.setWorkingDir() call).

When using the Ant tasks, you can specify the log file by using the log attribute. For example:

Code Block
<cargo containerId="resin3x" [...] log="target/cargo.log"/>