Provide CustomFieldSupplier example in Sample

Add a message counter to Spring Boot sample app to show creation
of additional fields by custom code. It counts all messages generated
by the sample application. This is also helpful to detect missing messages
in downstream logging systems.

Signed-off-by: Karsten Schnitter <[email protected]>

Author: KarstenSchnitter

sample-spring-boot/src/main/java/com/sap/hcp/cf/logging/sample/springboot/statistics/StatisticsContextFieldSupplier.java

@@ -0,0 +1,25 @@
+package com.sap.hcp.cf.logging.sample.springboot.statistics;
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.atomic.AtomicLong;
+
+import com.sap.hcp.cf.logging.common.serialization.ContextFieldSupplier;
+
+public class StatisticsContextFieldSupplier implements ContextFieldSupplier {
+
+	private static final String KEY = "message_count";
+
+	private static AtomicLong count = new AtomicLong();
+
+	@SuppressWarnings("serial")
+	@Override
+	public Map<String, Object> get() {
+		return new HashMap<String, Object>() {
+			{
+				put(KEY, count.incrementAndGet());
+			}
+		};
+	}
+
+}

sample-spring-boot/src/main/resources/log4j2.xml

@@ -7,7 +7,11 @@
 
 	<Appenders>
 		<Console name="STDOUT-JSON" target="SYSTEM_OUT" follow="true">
-			<JsonPatternLayout charset="utf-8" />
+			<JsonPatternLayout charset="utf-8">
+				<contextFieldSupplier class="com.sap.hcp.cf.logging.sample.springboot.statistics.StatisticsContextFieldSupplier" />
+				<!-- Uncomment to send message count as nested custom field: -->
+				<!-- <customField mdcKeyName="message_count" /> -->
+			</JsonPatternLayout>
 		</Console>
 		<Console name="STDOUT" target="SYSTEM_OUT" follow="true">
 			<PatternLayout

sample-spring-boot/src/main/resources/logback.xml

@@ -1,22 +1,29 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE xml>
 <configuration debug="false" scan="false">
-    <turboFilter class="com.sap.hcp.cf.logback.filter.DynamicLevelPrefixLoggerTurboFilter" />
-    <!-- write logs to console -->
-    <appender name="STDOUT-JSON" class="ch.qos.logback.core.ConsoleAppender">
-        <!-- encode and enrich full message with the required fields/tags -->
-        <encoder class="com.sap.hcp.cf.logback.encoder.JsonEncoder" />
-    </appender>
-    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
-        <encoder>
-            <pattern>%d %-5level [%thread] %logger{0} [%mdc]>: %msg
-                %replace(%xEx){'\n', ' | '}%nopex%n</pattern>
-        </encoder>
-    </appender>
-    <!-- default log level for all loggers is INFO by default -->
-    <root level="${LOG_ROOT_LEVEL:-INFO}">
-        <appender-ref ref="STDOUT-JSON" />
-    </root>
+	<turboFilter
+		class="com.sap.hcp.cf.logback.filter.DynamicLevelPrefixLoggerTurboFilter" />
+	<!-- write logs to console -->
+	<appender name="STDOUT-JSON"
+		class="ch.qos.logback.core.ConsoleAppender">
+		<!-- encode and enrich full message with the required fields/tags -->
+		<encoder class="com.sap.hcp.cf.logback.encoder.JsonEncoder">
+			<contextFieldSupplier>com.sap.hcp.cf.logging.sample.springboot.statistics.StatisticsContextFieldSupplier</contextFieldSupplier>
+			<!-- Uncomment to send message count as nested custom field: -->
+			<!-- <customFieldMdcKeyName>message_count</customFieldMdcKeyName> -->
+		</encoder>
+	</appender>
+	<appender name="STDOUT"
+		class="ch.qos.logback.core.ConsoleAppender">
+		<encoder>
+			<pattern>%d %-5level [%thread] %logger{0} [%mdc]>: %msg
+				%replace(%xEx){'\n', ' | '}%nopex%n</pattern>
+		</encoder>
+	</appender>
+	<!-- default log level for all loggers is INFO by default -->
+	<root level="${LOG_ROOT_LEVEL:-INFO}">
+		<appender-ref ref="STDOUT-JSON" />
+	</root>
 
-    <logger name="com.sap.hcp.cf" level="${LOG_HCP_CF_LEVEL:-INFO}" />
+	<logger name="com.sap.hcp.cf" level="${LOG_HCP_CF_LEVEL:-INFO}" />
 </configuration>