Chapter 4. Debugging your Spring Boot-based application

Procedure

1. In a console, navigate to the directory with your application.

2. Launch your application and specify the necessary JVM arguments and the debug port using the following syntax:

   $ mvn spring-boot:run -Drun.jvmArguments="-Xdebug -Xrunjdwp:transport=dt_socket,server=y,suspend=n,address=$PORT_NUMBER"

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   $PORT_NUMBER is an unused port number of your choice. Remember this number for the remote debugger configuration.

   If you want the JVM to pause and wait for remote debugger connection before it starts the application, change suspend to y.

Procedure

1. In a console, navigate to the directory with the uberjar.

2. Execute the uberjar with the following parameters. Ensure that all the parameters are specified before the name of the uberjar on the line.

   $ java -agentlib:jdwp=transport=dt_socket,server=y,suspend=n,address=$PORT_NUMBER -jar $UBERJAR_FILENAME

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   $PORT_NUMBER is an unused port number of your choice. Remember this number for the remote debugger configuration.

   If you want the JVM to pause and wait for remote debugger connection before it starts the application, change suspend to y.

Procedure

1. Using the oc command, list the available deployment configurations:

   $ oc get dc

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2. Set the JAVA_DEBUG environment variable in the deployment configuration of your application to true, which configures the JVM to open the port number 5005 for debugging. For example:

   $ oc set env dc/MY_APP_NAME JAVA_DEBUG=true

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3. Redeploy the application if it is not set to redeploy automatically on configuration change. For example:

   $ oc rollout latest dc/MY_APP_NAME

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4. Configure port forwarding from your local machine to the application pod:

   1. List the currently running pods and find one containing your application:

      $ oc get pod
      NAME                            READY     STATUS      RESTARTS   AGE
      MY_APP_NAME-3-1xrsp          0/1       Running     0          6s
      ...

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   2. Configure port forwarding:

      $ oc port-forward MY_APP_NAME-3-1xrsp $LOCAL_PORT_NUMBER:5005

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      Here, $LOCAL_PORT_NUMBER is an unused port number of your choice on your local machine. Remember this number for the remote debugger configuration.

5. When you are done debugging, unset the JAVA_DEBUG environment variable in your application pod. For example:

   $ oc set env dc/MY_APP_NAME JAVA_DEBUG-

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Procedure

1. Start Red Hat CodeReady Studio.

2. Create a new debug configuration for your application:

   1. Click Run→Debug Configurations.
   2. In the list of configurations, double-click Remote Java application. This creates a new remote debugging configuration.
   3. Enter a suitable name for the configuration in the Name field.
   4. Enter the path to the directory with your application into the Project field. You can use the Browse…​ button for convenience.
   5. Set the Connection Type field to Standard (Socket Attach) if it is not already.
   6. Set the Port field to the port number that your application is listening on for debugging.
   7. Click Apply.

3. Start debugging by clicking the Debug button in the Debug Configurations window.

   To quickly launch your debug configuration after the first time, click Run→Debug History and select the configuration from the list.

Procedure

1. Declare a org.apache.commons.logging.Log object using the org.apache.commons.logging.LogFactory for the class you want to add logging.

   import org.apache.commons.logging.Log;
   import org.apache.commons.logging.LogFactory;
   ...
   private static Log logger = LogFactory.getLog(TheClass.class);

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2. Add debugging statements using logger.debug("my logging message").

   Example logging statement

   @GET
   @Path("/greeting")
   @Produces("application/json")
   public Greeting greeting(@QueryParam("name") @DefaultValue("World") String name) {
       String message = String.format(properties.getMessage(), name);
   
       logger.debug("Message: " + message);
   
       return new Greeting(message);
   }

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3. Add a logging.level.fully.qualified.name.of.TheClass=DEBUG in src/main/resources/application.properties.

   For example, if you added a logging statement to dev.snowdrop.example.service.GreetingEndpoint you would use:

   logging.level.dev.snowdrop.example.service.GreetingEndpoint=DEBUG

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   This enables log messages at the DEBUG level and above to be shown in the logs for your class.

Procedure

1. Start your application.

   $ mvn spring-boot:run

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2. Test your application to invoke debug logging.

   $ curl http://localhost:8080/api/greeting?name=Sarah

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3. View your application logs to see your debug messages.

   dev.snowdrop.example.service.GreetingEndpoint     : Message: Hello, Sarah!

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Procedure

1. Deploy your application to OpenShift:

   $ mvn clean package -Popenshift -Ddekorate.deploy=true

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2. View the logs:

   1. Get the name of the pod with your application:

      $ oc get pods

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   2. Start watching the log output:

      $ oc logs -f pod/MY_APP_NAME-2-aaaaa

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      Keep the terminal window displaying the log output open so that you can watch the log output.

3. Interact with your application:

   1. Get the route of your application:

      $ oc get routes

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   2. Make an HTTP request on the /api/greeting endpoint of your application:

      $ curl $APPLICATION_ROUTE/api/greeting?name=Sarah

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4. Return to the window with your pod logs and inspect debug logging messages in the logs.

   dev.snowdrop.example.service.GreetingEndpoint     : Message: Hello, Sarah!

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5. To disable debug logging, remove logging.level.fully.qualified.name.of.TheClass=DEBUG from src/main/resources/application.properties and redeploy your application.