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| |
| |
| <section> |
| <h2><a name="Log4j_2_API"></a>Log4j 2 API</h2> |
| <section> |
| <h3><a name="Messages"></a>Messages</h3> |
| <a name="Messages"></a> |
| |
| <p> |
| Although Log4j 2 provides Logger methods that accept Strings and Objects, all of these are ultimately |
| captured in Message objects that are then associated with the log event. Applications are free to |
| construct Messages of their own and pass them to the Logger. Although it may seem more expensive than |
| passing the message format and parameters directly to the event, testing has shown that with modern |
| JVMs the cost of creating and destroying events is minor, especially when complex tasks are encapsulated |
| in the Message instead of the application. In addition, when using the methods that accept Strings and |
| parameters, the underlying Message object will only be created if any configured global filters |
| or the Logger's log level allow the message to be processed. |
| </p> |
| |
| <p> |
| Consider an application that has a Map object containing {"Name" = "John Doe", "Address" = "123 Main |
| St.", |
| "Phone" = "(999) 555-1212"} and a User object that has a getId method that returns "jdoe". The developer |
| would like to add an informational message that returns "User John Doe has logged in using id jdoe". The |
| way this could be accomplished is by doing: |
| </p> |
| |
| <div> |
| <pre class="prettyprint">logger.info("User {} has logged in using id {}", map.get("Name"), user.getId());</pre></div> |
| |
| <p> |
| While there is nothing inherently wrong with this, as the complexity of the objects and desired output |
| increases this technique becomes harder to use. As an alternative, using Messages allows: |
| </p> |
| |
| <div> |
| <pre class="prettyprint">logger.info(new LoggedInMessage(map, user));</pre></div> |
| |
| <p> |
| In this alternative the formatting is delegated to the LoggedInMessage object's getFormattedMessage |
| method. |
| Although in this alternative a new object is created, none of the methods on the objects passed to the |
| LoggedInMessage are invoked until the LoggedInMessage is formatted. This is especially useful when an |
| Object's toString method does not produce the information you would like to appear in the log. |
| </p> |
| |
| <p> |
| Another advantage to Messages is that they simplify writing Layouts. In other logging frameworks the |
| Layout must loop through the parameters individually and determine what to do based on what objects |
| are encountered. With Messages the Layout has the option of delegating the formatting to the Message or |
| performing its formatting based on the type of Message encountered. |
| </p> |
| |
| <p> |
| Borrowing from the earlier example illustrating Markers to identify SQL statements being logged, Messages |
| can also be leveraged. First, the Message is defined. |
| </p> |
| |
| <div> |
| <pre class="prettyprint linenums"> |
| public class SQLMessage implements Message { |
| public enum SQLType { |
| UPDATE, |
| QUERY |
| }; |
| |
| private final SQLType type; |
| private final String table; |
| private final Map<String, String> cols; |
| |
| public SQLMessage(SQLType type, String table) { |
| this(type, table, null); |
| } |
| |
| public SQLMessage(SQLType type, String table, Map<String, String> cols) { |
| this.type = type; |
| this.table = table; |
| this.cols = cols; |
| } |
| |
| public String getFormattedMessage() { |
| switch (type) { |
| case UPDATE: |
| return createUpdateString(); |
| break; |
| case QUERY: |
| return createQueryString(); |
| break; |
| default; |
| } |
| } |
| |
| public String getMessageFormat() { |
| return type + " " + table; |
| } |
| |
| public Object getParameters() { |
| return cols; |
| } |
| |
| private String createUpdateString() { |
| } |
| |
| private String createQueryString() { |
| } |
| |
| 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> |
| Next we can use the message in our application. |
| </p> |
| |
| <div> |
| <pre class="prettyprint linenums"> |
| 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, new SQLMessage(SQLMessage.SQLType.QUERY, table)); |
| |
| return logger.exit(); |
| } |
| |
| public String doUpdate(String table, Map<String, String> params) { |
| logger.entry(param); |
| |
| logger.debug(UPDATE_MARKER, new SQLMessage(SQLMessage.SQLType.UPDATE, table, parmas); |
| |
| return logger.exit(); |
| } |
| }</pre></div> |
| |
| <p> |
| Notice that in contrast to the prior version of this example, the logger.debug in doUpdate no longer |
| needs to be wrapped in an isDebugEnabled call as creation of the SQLMessage is on the same order of |
| magnitude of performing that check. Furthermore, all the formatting of the SQL columns is now hidden |
| in the SQLMessage instead of having to take place in the business logic. Finally, if desired, Filters |
| and/or Layouts can be written to take special action when an SQLMessage is encountered. |
| </p> |
| <section> |
| <h4><a name="FormattedMessage"></a>FormattedMessage</h4> |
| <a name="FormattedMessage"></a> |
| |
| <p> |
| The message pattern passed to a |
| <a href="../log4j-api/apidocs/org/apache/logging/log4j/message/FormattedMessage.html" class="javadoc">FormattedMessage</a> |
| is first checked to see if it is a valid java.text.MessageFormat pattern. If it is, a MessageFormatMessage is |
| used to format it. If not it is next checked to see if it contains any tokens that are valid format |
| specifiers for String.format(). If so, a StringFormattedMessage is used to format it. Finally, if the |
| pattern doesn't match either of those then a ParameterizedMessage is used to format it. |
| </p> |
| </section><section> |
| <h4><a name="LocalizedMessage"></a>LocalizedMessage</h4> |
| <a name="LocalizedMessage"></a> |
| |
| <p> |
| <a href="../log4j-api/apidocs/org/apache/logging/log4j/message/LocalizedMessage.html" class="javadoc">LocalizedMessage</a> |
| is provided primarily to provide compatibility with Log4j 1.x. Generally, |
| the best approach to localization is to have the client UI render the events in the client's locale. |
| </p> |
| |
| <p> |
| LocalizedMessage incorporates a ResourceBundle and allows the message pattern parameter to be the key to |
| the message pattern in the bundle. If no bundle is specified, |
| LocalizedMessage will attempt to locate a bundle with the name of the Logger used to log the event. The |
| message retrieved from the bundle will be formatted using a FormattedMessage. |
| </p> |
| </section><section> |
| <h4><a name="LoggerNameAwareMessage"></a>LoggerNameAwareMessage</h4> |
| <a name="LoggerNameAwareMessage"></a> |
| |
| <p> |
| LoggerNameAwareMessage is an interface with a setLoggerName method. This method will be called during |
| event construction so that the Message has the name of the Logger used to log the event when the |
| message is being formatted. |
| </p> |
| </section><section> |
| <h4><a name="MapMessage"></a>MapMessage</h4> |
| <a name="MapMessage"></a> |
| |
| <p> |
| A MapMessage contains a Map of String keys and values. MapMessage implements |
| FormattedMessage and accepts format specifiers of "XML", "JSON" or "JAVA", in which case the Map |
| will be formatted as XML, JSON or as documented by |
| <a class="javadoc" href="https://docs.oracle.com/javase/7/docs/api/java/util/AbstractMap.html#toString()">java.util.AbstractMap.toString()</a>. |
| Otherwise, the Map will be formatted as "key1=value1 key2=value2 ...". |
| </p> |
| |
| <p> |
| Some Appenders make special use of MapMessage objects: |
| </p> |
| |
| <ul> |
| |
| <li> |
| When a <a href="appenders.html#JMSAppender">JMS Appender</a> is configured with a MessageLayout, it converts a Log4j |
| MapMessage to a JMS javax.jms.MapMessage. |
| </li> |
| |
| <li> |
| When a <a href="appenders.html#JDBCAppender">JDBC Appender</a> is configured with a MessageLayout, it converts a Log4j |
| MapMessage to values in a SQL INSERT statement. |
| </li> |
| |
| <li> |
| When a <a href="appenders.html#NoSQLAppenderMongoDB2">MongoDB2 Appender</a> or |
| <a href="appenders.html#NoSQLAppenderMongoDB3">MongoDB3 Appender</a> is configured with a MessageLayout, it converts a Log4j |
| MapMessage to fields in a MongoDB object. |
| </li> |
| </ul> |
| |
| <p> |
| When an Appender is MessageLayout-aware, the object Log4j sends to target is not a Log4j Log |
| Event but a custom object. |
| </p> |
| </section><section> |
| <h4><a name="MessageFormatMessage"></a>MessageFormatMessage</h4> |
| <a name="MessageFormatMessage"></a> |
| |
| <p> |
| <a href="../log4j-api/apidocs/org/apache/logging/log4j/message/MessageFormatMessage.html" class="javadoc">MessageFormatMessage</a> |
| handles messages that use a <a class="externalLink" href="https://docs.oracle.com/javase/7/docs/api/java/text/MessageFormat.html">conversion format</a>. |
| While this Message has more flexibility than ParameterizedMessage, it is also about two times slower. |
| </p> |
| </section><section> |
| <h4><a name="MultiformatMessage"></a>MultiformatMessage</h4> |
| <a name="MultiformatMessage"></a> |
| |
| <p> |
| A MultiformatMessage will have a getFormats method and a getFormattedMessage method that accepts and array |
| of format Strings. The getFormats method may be called by a Layout to provide it information on what |
| formatting options the Message supports. The Layout may then call getFormattedMessage with one or more |
| for the formats. If the Message doesn't recognize the format name it will simply format the data using its |
| default format. An example of this is the StructuredDataMessage which accepts a format String of "XML" |
| which will cause it to format the event data as XML instead of the RFC 5424 format. |
| </p> |
| </section><section> |
| <h4><a name="ObjectMessage"></a>ObjectMessage</h4> |
| <a name="ObjectMessage"></a> |
| |
| <p> |
| Formats an Object by calling its toString method. Since Log4j 2.6, Layouts trying to be low-garbage or |
| garbage-free will call the formatTo(StringBuilder) method instead. |
| </p> |
| </section><section> |
| <h4><a name="ParameterizedMessage"></a>ParameterizedMessage</h4> |
| <a name="ParameterizedMessage"></a> |
| |
| <p> |
| <a href="../log4j-api/apidocs/org/apache/logging/log4j/message/ParameterizedMessage.html" class="javadoc">ParameterizedMessage</a> |
| handles messages that contain "{}" in the format to represent replaceable tokens and the replacement |
| parameters. |
| </p> |
| </section><section> |
| <h4><a name="ReusableObjectMessage"></a>ReusableObjectMessage</h4> |
| <a name="ReusableObjectMessage"></a> |
| |
| <p> |
| In garbage-free mode, this message is used to pass logged Objects to the Layout and Appenders. |
| Functionally equivalent to <a href="#ObjectMessage">ObjectMessage</a>. |
| </p> |
| </section><section> |
| <h4><a name="ReusableParameterizedMessage"></a>ReusableParameterizedMessage</h4> |
| <a name="ReusableParameterizedMessage"></a> |
| |
| <p> |
| In garbage-free mode, this message is used to handle messages that contain "{}" in the format to |
| represent replaceable tokens and the replacement parameters. |
| Functionally equivalent to <a href="#ParameterizedMessage">ParameterizedMessage</a>. |
| </p> |
| </section><section> |
| <h4><a name="ReusableSimpleMessage"></a>ReusableSimpleMessage</h4> |
| <a name="ReusableSimpleMessage"></a> |
| |
| <p> |
| In garbage-free mode, this message is used to pass logged Strings and CharSequences to the Layout and Appenders. |
| Functionally equivalent to <a href="#SimpleMessage">SimpleMessage</a>. |
| </p> |
| </section><section> |
| <h4><a name="SimpleMessage"></a>SimpleMessage</h4> |
| <a name="SimpleMessage"></a> |
| |
| <p> |
| SimpleMessage contains a String or CharSequence that requires no formatting. |
| </p> |
| </section><section> |
| <h4><a name="StringFormattedMessage"></a>StringFormattedMessage</h4> |
| <a name="StringFormattedMessage"></a> |
| |
| <p> |
| <a href="../log4j-api/apidocs/org/apache/logging/log4j/message/StringFormattedMessage.html" class="javadoc">StringFormattedMessage</a> |
| handles messages that use a <a class="externalLink" href="https://docs.oracle.com/javase/7/docs/api/java/util/Formatter.html#syntax">conversion format</a> |
| that is compliant with <a class="javadoc" href="https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#format(java.lang.String, java.lang.Object...)">java.lang.String.format()</a>. |
| While this Message has more flexibility than ParameterizedMessage, it is also 5 to 10 times slower. |
| </p> |
| </section><section> |
| <h4><a name="StructuredDataMessage"></a>StructuredDataMessage</h4> |
| <a name="StructuredDataMessage"></a> |
| |
| <p> |
| <a href="../log4j-api/apidocs/org/apache/logging/log4j/message/StructuredDataMessage.html" class="javadoc">StructuredDataMessage</a> |
| allows applications to add items to a Map as well as set the id to allow a message to be formatted as a |
| Structured Data element in accordance with <a class="externalLink" href="http://tools.ietf.org/html/rfc5424">RFC 5424</a>. |
| </p> |
| </section><section> |
| <h4><a name="ThreadDumpMessage"></a>ThreadDumpMessage</h4> |
| <a name="ThreadDumpMessage"></a> |
| |
| <p> |
| A ThreadDumpMessage, if logged, will generate stack traces for all threads. |
| The stack traces will include any locks that are held. |
| </p> |
| </section><section> |
| <h4><a name="TimestampMessage"></a>TimestampMessage</h4> |
| <a name="TimestampMessage"></a> |
| |
| <p> |
| A TimestampMessage will provide a getTimestamp method that is called during event construction. The |
| timestamp in the Message will be used in lieu of the current timestamp. |
| </p> |
| </section></section> |
| </section> |
| |
| |
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