logback-android/src/main/java/ch/qos/logback/classic/util/LogbackMDCAdapter.java
public String get(String key) {
    final Map<String, String> map = copyOnThreadLocal.get();
    if ((map != null) && (key != null)) {
      return map.get(key);
    } else {
      return null;
    }
  }
public String get(String key) {
    final Map<String, String> map = copyOnThreadLocal.get();
    if ((map != null) && (key != null)) {
      return map.get(key);
    } else {
      return null;
    }
  }
Get the context identified by the <code>key</code> parameter.