Add source for blog

Author: rewolf

README.md

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+# Extending Log4j2 Demo 
+This project code accompanies a blog found at 
+
+https://andrew-flower.com/blog/Create_Custom_Log4j_Plugins
+
+It demos a method of extending Log4j2 using Converters as well as a 
+method for testing the converter
+
+## Running the test
+Type the following command to run the tests using Maven. 
+You will need Maven installed of course
+```
+mvn install
+```

pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+ xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+ xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+<modelVersion>4.0.0</modelVersion>
+
+<groupId>com.andrew_flower.demo</groupId>
+<artifactId>blog-extending-log4j2</artifactId>
+<version>1.0.0</version>
+
+<dependencies>
+<dependency>
+<groupId>org.apache.logging.log4j</groupId>
+<artifactId>log4j-api</artifactId>
+<version>2.1</version>
+</dependency>
+<dependency>
+<groupId>org.apache.logging.log4j</groupId>
+<artifactId>log4j-core</artifactId>
+<version>2.1</version>
+</dependency>
+<dependency>
+<groupId>junit</groupId>
+<artifactId>junit</artifactId>
+<version>4.9</version>
+<scope>test</scope>
+</dependency>
+</dependencies>
+
+<repositories>
+<repository>
+<id>central</id>
+<url>http://repo1.maven.org/maven2/</url>
+</repository>
+</repositories>
+</project>

src/main/java/com/andrew_flower/example/MythicalApplicationRequestHandler.java

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+package com.andrew_flower.example;
+
+/**
+ * Created on 15/2/20.
+ *
+ * @author rewolf
+ */
+public class MythicalApplicationRequestHandler {
+ private static MythicalApplicationRequestHandler instance = null;
+
+ public synchronized static MythicalApplicationRequestHandler getInstance() {
+ if (instance == null) {
+ instance = new MythicalApplicationRequestHandler();
+ }
+ return instance;
+ }
+
+ public synchronized static void setInstance(MythicalApplicationRequestHandler instance) {
+ MythicalApplicationRequestHandler.instance = instance;
+ }
+
+ public String getCurrentRequestId() {
+ return "abcd-efgh-1234-5678";
+ }
+}

src/main/java/com/andrew_flower/example/ReqIdConverter.java

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+package com.andrew_flower.example;
+
+import org.apache.logging.log4j.core.LogEvent;
+import org.apache.logging.log4j.core.config.plugins.Plugin;
+import org.apache.logging.log4j.core.pattern.*;
+
+/**
+ * @author rewolf
+ */
+@Plugin(name = "ReqIdConverter", category = "Converter")
+@ConverterKeys({"reqId"})
+public class ReqIdConverter extends LogEventPatternConverter {
+ protected ReqIdConverter(String name, String style) {
+ super(name, style);
+ }
+
+ public static ReqIdConverter newInstance(String[] options) {
+ return new ReqIdConverter("reqId", "reqId");
+ }
+
+ @Override
+ public void format(LogEvent event, StringBuilder toAppendTo) {
+ toAppendTo.append(getReqId());
+ }
+
+ protected String getReqId() {
+ String reqId = MythicalApplicationRequestHandler.getInstance().getCurrentRequestId();
+ if (reqId == null) {
+ reqId = "-";
+ }
+ return reqId;
+ }
+}

src/main/java/com/andrew_flower/example/StringAppender.java

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+package com.andrew_flower.example;
+
+import org.apache.logging.log4j.*;
+import org.apache.logging.log4j.core.*;
+import org.apache.logging.log4j.core.appender.*;
+import org.apache.logging.log4j.core.config.*;
+import org.apache.logging.log4j.core.layout.PatternLayout;
+
+import java.io.*;
+
+/**
+ * @author rewolf
+ */
+public class StringAppender extends AbstractOutputStreamAppender<StringAppender.StringOutputStreamManager> {
+ static LoggerContext context = (LoggerContext) LogManager.getContext(false);
+ static Configuration configuration = context.getConfiguration();
+ StringOutputStreamManager manager;
+
+ private StringAppender(String name, Layout<? extends Serializable> layout, Filter filter, StringOutputStreamManager manager, boolean ignoreExceptions, boolean immediateFlush) {
+ super(name, layout, filter, ignoreExceptions, immediateFlush, manager);
+ this.manager = manager;
+ }
+
+ public static StringAppender createStringAppender(String nullablePatternString) {
+ ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+ PatternLayout layout;
+ if (nullablePatternString == null) {
+ layout = PatternLayout.createDefaultLayout();
+ } else {
+ layout = PatternLayout.createLayout(nullablePatternString, configuration, null, null, true, false, null, null);
+ }
+
+ return new StringAppender(
+ "StringAppender",
+ layout,
+ null,
+ new StringOutputStreamManager(outputStream, "StringStream", layout),
+ false,
+ true);
+ }
+
+ public void addToLogger(String loggerName, Level level) {
+ LoggerConfig loggerConfig = configuration.getLoggerConfig(loggerName);
+ loggerConfig.addAppender(this, level, null);
+ context.updateLoggers();
+ }
+
+ public void removeFromLogger(String loggerName) {
+ LoggerConfig loggerConfig = configuration.getLoggerConfig(loggerName);
+ loggerConfig.removeAppender("StringAppender");
+ context.updateLoggers();
+ }
+
+ public String getOutput() {
+ manager.flush();
+ return new String(manager.getStream().toByteArray());
+ }
+
+ /**
+ * StringOutputStreamManager to manage an in memory byte-stream representing our stream
+ */
+ protected static class StringOutputStreamManager extends OutputStreamManager {
+ ByteArrayOutputStream stream;
+
+ protected StringOutputStreamManager(ByteArrayOutputStream os, String streamName, Layout<?> layout) {
+ super(os, streamName, layout);
+ stream = os;
+ }
+
+ public ByteArrayOutputStream getStream() {
+ return stream;
+ }
+ }
+}

src/test/java/com/andrew_flower/example/LogConverterTest.java

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+package com.andrew_flower.example;
+
+
+import org.apache.logging.log4j.Level;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * @author rewolf
+ */
+public class LogConverterTest {
+ private final static String STUB_REQ_ID = "Haro-I-Id";
+
+ @Before
+ public void setup() {
+ MythicalApplicationRequestHandler stub = new MythicalApplicationRequestHandler() {
+ @Override
+ public String getCurrentRequestId() {
+ return STUB_REQ_ID;
+ }
+ };
+ MythicalApplicationRequestHandler.setInstance(stub);
+ }
+
+ @Test
+ public void formatAppendsRequestId() throws Exception {
+ ReqIdConverter converter = ReqIdConverter.newInstance(new String[]{});
+ StringBuilder message = new StringBuilder().append("BEFORE_");
+
+ converter.format(null, message);
+
+ assertEquals("BEFORE_" + STUB_REQ_ID, message.toString());
+ }
+
+ @Test
+ public void logReplacesKeyWithReqId() throws Exception {
+ // Get the RootLogger which, if you don't have log4j2-test.xml defined, will only log ERRORs
+ Logger logger = LogManager.getRootLogger();
+ // Create a String Appender to capture log output
+ StringAppender appender = StringAppender.createStringAppender("[%reqId] %m");
+ appender.addToLogger(logger.getName(), Level.INFO);
+ appender.start();
+
+ // Log to the string appender
+ logger.error("Test");
+
+ assertEquals("[" + STUB_REQ_ID + "] Test", appender.getOutput());
+ appender.removeFromLogger(LogManager.getRootLogger().getName());
+ }
+}