Advanced Usage

By default all ThreadContext parameters are stored under the “Context Data” tab in sentry.io.

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import org.apache.logging.log4j.ThreadContext;

void logWithExtras() {
  // ThreadContext ("MDC") extras
  ThreadContext.put("Environment", "Development");
  ThreadContext.put("OS", "Linux");

  // This sends an event where the Environment and OS ThreadContext values are set as Context Data entries
  logger.error("This is a test");
}

Note that ThreadContext manages data on a per-thread basis, and that a child thread does not automatically inherit ThreadContext properties from its parent.

In Practice

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import io.sentry.core.Sentry;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.ThreadContext;

public class MyClass {
  private static final Logger logger = LogManager.getLogger(MyClass.class);

  void logSimpleMessage() {
    // This sends a simple event to Sentry
    logger.error("This is a test");
  }

  void logWithBreadcrumbs() {
    // Record a breadcrumb that will be sent with the next event(s),
    // by default the last 100 breadcrumbs are kept.
    Sentry.addBreadcrumb("User made an action");

    // Log entries below `minimumEventLevel` and above or equal to `minimumBreadcrumbLevel`
    // are recorded as breadcrumbs
    logger.info("User made another action");

    // This sends a simple event to Sentry
    logger.error("This is a test");
  }

  void logWithExtras() {
    // MDC extras
    ThreadContext.put("extra_key", "extra_value");
    // NDC extras are sent under 'log4j2-NDC'
    ThreadContext.push("Extra_details");
    // This sends an event with extra data to Sentry
    logger.error("This is a test");
  }

  void logException() {
    try {
      unsafeMethod();
    } catch (Exception e) {
      // This sends an exception event to Sentry
      logger.error("Exception caught", e);
    }
  }

  void unsafeMethod() {
    throw new UnsupportedOperationException("You shouldn't call this!");
  }
}

Context Tags

Since Sentry 6.0.0, it is possible to define a list of MDC tags that will show up as Tags in the Sentry UI. MDC Tags not in this list are shown as Context Data in the UI, just like before. To define such tags add a context-tags attribute to the <Sentry> tag in your log4j2.xml with the tags as comma seperated items.

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<Sentry name="Sentry"
  dsn="https://examplePublicKey@o0.ingest.sentry.io/0"
  contextTags="userId,requestId"
/>

When calling ThreadContext.push("userId", "myUserId") with above Appender configuration in place, the userId will show up as a Tag on the event in the Sentry UI.

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