Create Custom Filter for the AsyncAppender

application/build.gradle

@@ -47,8 +47,7 @@ dependencies {
 
     implementation 'net.dv8tion:JDA:4.4.0_351'
 
-    compileOnly 'org.apache.logging.log4j:log4j-api:2.16.0'
-    runtimeOnly 'org.apache.logging.log4j:log4j-core:2.16.0'
+    implementation 'org.apache.logging.log4j:log4j-core:2.16.0'
     runtimeOnly 'org.apache.logging.log4j:log4j-slf4j18-impl:2.16.0'
 
     implementation 'org.jooq:jooq:3.15.3'

application/src/main/java/org/togetherjava/tjbot/logging/FlaggedFilter.java

@@ -0,0 +1,68 @@
+package org.togetherjava.tjbot.logging;
+
+import org.apache.logging.log4j.core.Core;
+import org.apache.logging.log4j.core.Filter;
+import org.apache.logging.log4j.core.LogEvent;
+import org.apache.logging.log4j.core.config.plugins.Plugin;
+import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
+import org.apache.logging.log4j.core.config.plugins.PluginFactory;
+import org.apache.logging.log4j.core.filter.AbstractFilter;
+import org.jetbrains.annotations.NotNull;
+
+
+/**
+ * A custom Filter for Log4j2, which only lets an event pass through if a Logging Flag is set in the
+ * environment. Intended to be used for local development for devs do not want to also run the
+ * logviewer project. No errors in console or Log should appear, if the Flag is not set and the
+ * logviewer is not running.
+ */
+@Plugin(name = "FlaggedFilter", category = Core.CATEGORY_NAME, elementType = Filter.ELEMENT_TYPE)
+public class FlaggedFilter extends AbstractFilter {
+
+    /**
+     * The environment Variable that needs to bet set in order for this Filter to let events through
+     */
+    public static final String LOGGING_FLAG = "TJ_APPENDER";
+
+    /**
+     * Create a FlaggedFilter.
+     *
+     * @param onMatch The action to take on a match.
+     * @param onMismatch The action to take on a mismatch.
+     */
+    public FlaggedFilter(@NotNull Result onMatch, @NotNull Result onMismatch) {
+        super(onMatch, onMismatch);
+    }
+
+    /**
+     * The actual filtering occurs here. If the Flag {@link #LOGGING_FLAG} is not set returns
+     * {@link Result#DENY} so nothing goes through. If the Flag is set it returns
+     * {@link Result#NEUTRAL} so other configured Filter still work.
+     *
+     * @param event The Event to log.
+     * @return {@link Result#DENY} if the Flag is not set, else {@link Result#NEUTRAL}
+     */
+    @Override
+    public Result filter(LogEvent event) {
+        return isLoggingEnabled() ? Result.NEUTRAL : Result.DENY;
+    }
+
+    boolean isLoggingEnabled() {
+        return System.getenv().containsKey(LOGGING_FLAG);
+    }
+
+    /**
+     * Required by the Log4j2 - Plugin framework in order to create an instance of this Filter.
+     *
+     * @param onMatch The action to take on a match.
+     * @param onMismatch The action to take on a mismatch.
+     * @return The created FlaggedFilter.
+     */
+    @PluginFactory
+    public static FlaggedFilter createFilter(
+            @NotNull @PluginAttribute(value = "onMatch", defaultString = "NEUTRAL") Result onMatch,
+            @NotNull
+            @PluginAttribute(value = "onMismatch", defaultString = "DENY") Result onMismatch) {
+        return new FlaggedFilter(onMatch, onMismatch);
+    }
+}

application/src/main/java/org/togetherjava/tjbot/logging/package-info.java

@@ -0,0 +1,4 @@
+/**
+ * This package is for custom logging plugins of the bot.
+ */
+package org.togetherjava.tjbot.logging;

application/src/main/resources/log4j2.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<Configuration status="WARN" monitorInterval="30">
+<Configuration status="WARN" monitorInterval="30" packages="org.togetherjava.tjbot.logging">
     <Appenders>
         <Console name="Console" target="SYSTEM_OUT">
             <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
@@ -17,6 +17,7 @@
             <JsonLayout/>
         </Http>
         <Async name="AsyncHttp">
+            <FlaggedFilter/>
             <AppenderRef ref="Http"/>
         </Async>
     </Appenders>

application/src/test/java/org/togetherjava/tjbot/logging/FilterTest.java

@@ -0,0 +1,36 @@
+package org.togetherjava.tjbot.logging;
+
+import org.apache.logging.log4j.core.Filter;
+import org.apache.logging.log4j.core.LogEvent;
+import org.apache.logging.log4j.core.impl.Log4jLogEvent;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+
+class FilterTest {
+
+    FlaggedFilter filter;
+    LogEvent event;
+
+    @BeforeEach
+    void setUp() {
+        this.filter = FlaggedFilter.createFilter(Filter.Result.NEUTRAL, Filter.Result.DENY);
+        this.event = Log4jLogEvent.newBuilder().build();
+    }
+
+    @Test
+    void shouldPassFilter() {
+        FlaggedFilter spy = Mockito.spy(this.filter);
+        Mockito.when(spy.isLoggingEnabled()).thenReturn(true);
+        Assertions.assertEquals(Filter.Result.NEUTRAL, spy.filter(this.event));
+    }
+
+
+    @Test
+    void shouldNotPassFilter() {
+        FlaggedFilter spy = Mockito.spy(this.filter);
+        Mockito.when(spy.isLoggingEnabled()).thenReturn(false);
+        Assertions.assertEquals(Filter.Result.DENY, spy.filter(this.event));
+    }
+}