---
title: "Advanced Usage"
description: "Learn about adding extra data using the MDC system provided by Logback."
url: https://docs.sentry.io/platforms/java/guides/logback/usage/advanced-usage/
---

# Advanced Usage | Sentry for Logback

It’s possible to add extra data to events thanks to [the MDC system provided by Logback](https://logback.qos.ch/manual/mdc.html).

#### [Mapped Tags](https://docs.sentry.io/platforms/java/guides/logback/usage/advanced-usage.md#mapped-tags)

By default all MDC parameters are stored under the “MDC” tab in Sentry.

```java
import org.slf4j.MDC;

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

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

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

### [In Practice](https://docs.sentry.io/platforms/java/guides/logback/usage/advanced-usage.md#in-practice)

```java
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.MDC;

public class MyClass {
  private static final Logger logger = LoggerFactory.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
    MDC.put("extra_key", "extra_value");
    // 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](https://docs.sentry.io/platforms/java/guides/logback/usage/advanced-usage.md#context-tags)

Starting with Sentry version 6.0.0 and up, you can define a list of `MDC tags` that will be viewable as `Tags` in the Sentry UI. `MDC Tags` not in this list will be viewable as `Context Data`.

As of Sentry Java SDK version 8.24.0, `contextTags` also applies to [structured logs](https://docs.sentry.io/product/explore/logs.md). MDC properties matching the configured `contextTags` will be attached to log entries as attributes, prefixed with "mdc.".

To define a tag that shall be sent with events and logs, add a `<contextTag>` entry inside the `<options>` of the Sentry appender configuration in `logback.xml`.

```xml
<appender name="sentry" class="io.sentry.logback.SentryAppender">
    <options>
      <!-- NOTE: Replace the test DSN below with YOUR OWN DSN to see the events from this app in your Sentry project/dashboard -->
      <dsn>___PUBLIC_DSN___</dsn>
      <contextTag>userId</contextTag>
      <contextTag>requestId</contextTag>
    </options>
  </appender>
```

When you call `MDC.put("userId", "myUserId")` with the above configuration in place, the `userId` will show up as a `tag` on the event in the Sentry UI.