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| |
| <div class="section"><h2>Log4j 2 API<a name="Log4j_2_API"></a></h2> |
| <a name="Markers"></a> |
| <div class="section"><h3>Markers<a name="Markers"></a></h3> |
| <p> |
| One of the primary purpose of a logging framework is to provide the means to generate debugging and |
| diagnostic information only when it is needed, and to allow filtering of that information so that it |
| does not overwhelm the system or the individuals who need to make use of it. As an example, an |
| application desires to log its entry, exit and other operations separately from SQL statements |
| being executed, and wishes to be able to log queries separate from updates. One way to accomplish |
| this is shown below: |
| </p> |
| <div class="source"><pre class="prettyprint"> import org.apache.logging.log4j.Logger; |
| import org.apache.logging.log4j.LogManager; |
| import java.util.Map; |
| |
| public class MyApp { |
| |
| private Logger logger = LogManager.getLogger(MyApp.class.getName()); |
| private static final Marker SQL_MARKER = MarkerManager.getMarker("SQL"); |
| private static final Marker UPDATE_MARKER = MarkerManager.getMarker("SQL_UPDATE", SQL_MARKER); |
| private static final Marker QUERY_MARKER = MarkerManager.getMarker("SQL_QUERY", SQL_MARKER); |
| |
| public String doQuery(String table) { |
| logger.entry(param); |
| |
| logger.debug(QUERY_MARKER, "SELECT * FROM {}", table); |
| |
| return logger.exit(); |
| } |
| |
| public String doUpdate(String table, Map<String, String> params) { |
| logger.entry(param); |
| |
| if (logger.isDebugEnabled()) { |
| logger.debug(UPDATE_MARKER, "UPDATE {} SET {}", table, formatCols); |
| |
| return logger.exit(); |
| } |
| |
| private String formatCols(Map<String, String> cols) { |
| StringBuilder sb = new StringBuilder(); |
| boolean first = true; |
| for (Map.Entry<String, String> entry : cols.entrySet()) { |
| if (!first) { |
| sb.append(", "); |
| } |
| sb.append(entry.getKey()).append("=").append(entry.getValue()); |
| first = false; |
| } |
| return sb.toString(); |
| } |
| }</pre></div> |
| <p> |
| In the example above it is now possible to add MarkerFilters to only allow SQL update operations |
| to be logged, all SQL updates to be logged or to log everything in MyApp. |
| </p> |
| <p> |
| Some important rules about Markers must be considered when using them. |
| </p><ol style="list-style-type: decimal"> |
| <li>Markers must be unique. They are permanently registered by name so care should be taken |
| to insure that Markers used in your application are distinct from those in the application's |
| dependencies, unless that is what is desired.</li> |
| <li>Like many objects in Log4J2, Markers are immutable. If a marker has a parent, the parent |
| must be named when the Marker is created and the parent cannot be changed after creation.</li> |
| <li>Markers only have a single parent. Markers can, however, have many children that reference |
| them.</li> |
| </ol> |
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