[BAEL-1300] Custom Logback Appender (#3193)

* BAEL-1300 Custom logback appender

* BAEL-1300 fix to logback module

* relativePath

logging-modules/logback/src/test/java/com/baeldung/logback/MapAppenderIntegrationTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.logback;
+
+import ch.qos.logback.classic.Logger;
+import org.junit.Before;
+import org.junit.Test;
+import org.slf4j.LoggerFactory;
+
+import static org.junit.Assert.assertEquals;
+
+public class MapAppenderIntegrationTest {
+
+    private Logger rootLogger;
+
+    @Before
+    public void setUp() throws Exception {
+        rootLogger = (Logger) LoggerFactory.getLogger("ROOT");
+    }
+
+    @Test
+    public void whenLoggerEmitsLoggingEvent_thenAppenderReceivesEvent() throws Exception {
+        rootLogger.info("Test from {}", this.getClass().getSimpleName());
+        MapAppender appender = (MapAppender) rootLogger.getAppender("map");
+        assertEquals(appender.getEventMap().size(), 1);
+    }
+
+    @Test
+    public void givenNoPrefixSet_whenLoggerEmitsEvent_thenAppenderReceivesNoEvent() throws Exception {
+        rootLogger.info("Test from {}", this.getClass().getSimpleName());
+        MapAppender appender = (MapAppender) rootLogger.getAppender("badMap");
+        assertEquals(appender.getEventMap().size(), 0);
+    }
+
+}

logging-modules/logback/src/test/java/com/baeldung/logback/MapAppenderTest.java

@@ -0,0 +1,60 @@
+package com.baeldung.logback;
+
+import ch.qos.logback.classic.Level;
+import ch.qos.logback.classic.LoggerContext;
+import ch.qos.logback.classic.spi.LoggingEvent;
+import ch.qos.logback.core.BasicStatusManager;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+public class MapAppenderTest {
+
+    private LoggerContext ctx;
+
+    private MapAppender mapAppender = new MapAppender();
+
+    private LoggingEvent event;
+
+    @Before
+    public void setUp() throws Exception {
+        ctx = new LoggerContext();
+        ctx.setName("test context");
+        ctx.setStatusManager(new BasicStatusManager());
+        mapAppender.setContext(ctx);
+        mapAppender.setPrefix("prefix");
+        event = new LoggingEvent("fqcn", ctx.getLogger("logger"), Level.INFO, "Test message for logback appender", null, new Object[0]);
+        ctx.start();
+    }
+
+    @After
+    public void tearDown() throws Exception {
+        ctx.stop();
+        mapAppender.stop();
+    }
+
+    @Test
+    public void whenPrefixIsNull_thenMapAppenderDoesNotLog() throws Exception {
+        mapAppender.setPrefix(null);
+        mapAppender.append(event);
+        assertTrue(mapAppender.getEventMap().isEmpty());
+    }
+
+    @Test
+    public void whenPrefixIsEmpty_thenMapAppenderDoesNotLog() throws Exception {
+        mapAppender.setPrefix("");
+        mapAppender.append(event);
+        assertTrue(mapAppender.getEventMap().isEmpty());
+    }
+
+    @Test
+    public void whenLogMessageIsEmitted_thenMapAppenderReceivesMessage() throws Exception {
+        mapAppender.append(event);
+        assertEquals(mapAppender.getEventMap().size(), 1);
+        mapAppender.getEventMap().forEach((k, v) -> assertTrue(k.startsWith("prefix")));
+    }
+
+}

logging-modules/logback/src/test/resources/logback-test.xml

@@ -0,0 +1,14 @@
+<configuration debug="true">
+
+    <appender name="map" class="com.baeldung.logback.MapAppender">
+        <prefix>test</prefix>
+    </appender>
+
+    <appender name="badMap" class="com.baeldung.logback.MapAppender"/>
+
+    <root level="debug">
+        <appender-ref ref="map"/>
+        <appender-ref ref="badMap"/>
+    </root>
+
+</configuration>