ReforgeHQ
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+# Reforge SDK Log4j2 Integration
+
+This module provides seamless integration between the Reforge SDK and Apache Log4j2, enabling dynamic log level management for your application.
+
+## Overview
+
+The Log4j2 integration uses an AbstractFilter to intercept logging calls and dynamically determine whether they should be logged based on log level configuration from Reforge. This allows you to:
+
+- **Centrally manage log levels** - Control logging across your entire application from the Reforge dashboard
+- **Real-time updates** - Change log levels without restarting your application
+- **Context-aware logging** - Different log levels for different loggers based on runtime context
+- **Performance** - Efficient filtering happens before log message construction
+
+## Installation
+
+Add the dependency to your `pom.xml`:
+
+```xml
+<dependency>
+    <groupId>com.reforge</groupId>
+    <artifactId>sdk-log4j2</artifactId>
+    <version>1.0.3</version>
+</dependency>
+```
+
+### Compatibility
+
+This module is compatible with:
+- **Log4j2 2.x** - The module uses only stable Log4j2 Core APIs (AbstractFilter, LoggerContext) that have been stable across Log4j2 2.x versions
+- **SLF4J 1.7.x and 2.0.x** (both work with Log4j2)
+
+**Note:** Log4j2 and SLF4J are marked as `provided` dependencies - your application's versions will be used automatically. We compile against Log4j2 2.19.0, but the APIs used are stable across the 2.x line. Log4j2 works with both SLF4J 1.7.x and 2.0.x.
+
+## Usage
+
+### Basic Setup (Programmatic)
+
+The simplest approach is to install the filter programmatically during application startup:
+
+```java
+import com.reforge.sdk.Sdk;
+import com.reforge.sdk.Options;
+import com.reforge.sdk.log4j2.ReforgeLog4j2Filter;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
+public class MyApplication {
+    private static final Logger log = LogManager.getLogger(MyApplication.class);
+
+    public static void main(String[] args) {
+        // Initialize the Reforge SDK
+        Sdk sdk = new Sdk(new Options());
+
+        // Install the Log4j2 filter
+        ReforgeLog4j2Filter.install(sdk.loggerClient());
+
+        // Now all your logging will respect Reforge log levels
+        log.info("Application started with dynamic log levels");
+    }
+}
+```
+
+**Important:**
+- Install the filter as early as possible in your application startup, ideally right after initializing the Reforge SDK
+- Install after Log4j2 is initialized
+- Any dynamic reconfiguration of Log4j2 (e.g., via JMX or programmatic changes) will remove the filter and it will need to be reinstalled
+
+### Configuration
+
+By default, the integration looks for a config key named `log-levels.default` of type `LOG_LEVEL_V2`. The configuration is evaluated with the following context:
+
+- `reforge-sdk-logging.lang`: `"java"`
+- `reforge-sdk-logging.logger-path`: The name of the logger (e.g., `"com.example.MyClass"`)
+
+You can customize the config key:
+
+```java
+Options options = new Options().setLoggerKey("my.custom.log.config");
+Sdk sdk = new Sdk(options);
+ReforgeLog4j2Filter.install(sdk.loggerClient());
+```
+
+### Example Reforge Configuration
+
+In your Reforge dashboard, create a `LOG_LEVEL_V2` config with key `log-levels.default`:
+
+```yaml
+# Default to INFO for all loggers
+default: INFO
+
+# Set specific packages to DEBUG
+rules:
+  - criteria:
+      logger-path:
+        starts-with: "com.example.services"
+    value: DEBUG
+
+  # Only log errors in noisy third-party library
+  - criteria:
+      logger-path:
+        starts-with: "com.thirdparty.noisy"
+    value: ERROR
+```
+
+## How It Works
+
+Once installed, the filter intercepts **all** logging calls across your entire application:
+
+- Works with **all loggers** (no need to configure individual loggers)
+- Works with **all appenders** (console, file, rolling, syslog, async, etc.)
+- Filters happen **before** log messages are formatted (performance benefit)
+- No modification of your existing Log4j2 configuration needed
+
+## Performance Considerations
+
+- **Efficient filtering**: Log level checks happen before expensive message construction
+- **Recursion protection**: Built-in guard prevents performance issues from recursive logging
+- **Caching**: The Reforge SDK caches configuration data to minimize network calls
+
+## Thread Safety
+
+The integration is fully thread-safe and uses Log4j2's built-in filter infrastructure, which is designed for concurrent access.
+
+## FAQ
+
+### Do I need to configure individual loggers?
+
+**No!** The filter works at the LoggerContext level and automatically intercepts all logging calls across your entire application without needing to configure individual loggers.
+
+### Do I need to modify my existing log4j2.xml?
+
+**No!** The filter works alongside your existing Log4j2 configuration. You don't need to change your appenders, layouts, or logger settings.
+
+### Does this work with all Log4j2 appenders?
+
+**Yes!** The filter intercepts logging decisions before they reach any appenders. It works with:
+- Console appenders
+- File appenders
+- Rolling file appenders
+- Syslog appenders
+- Async appenders
+- JDBC appenders
+- Custom appenders
+
+### What's the performance impact?
+
+Minimal! The filter:
+- Runs before log message formatting (avoiding expensive string operations for filtered logs)
+- Uses a ThreadLocal recursion guard to prevent infinite loops
+- Only makes one SDK call per log statement
+- The SDK caches configuration data to minimize network overhead
+
+### Can I use this in Spring Boot applications?
+
+**Yes!** Just install the filter in your main application class or a `@PostConstruct` method:
+
+```java
+@SpringBootApplication
+public class MyApplication {
+    @Autowired
+    private Sdk reforgeSDK;
+
+    @PostConstruct
+    public void setupLogging() {
+        ReforgeLog4j2Filter.install(reforgeSDK.loggerClient());
+    }
+
+    public static void main(String[] args) {
+        SpringApplication.run(MyApplication.class, args);
+    }
+}
+```
+
+### What happens if Log4j2 is reconfigured?
+
+If Log4j2 is dynamically reconfigured (via JMX, programmatic reconfiguration, or automatic file watching), the filter will be removed. You'll need to reinstall it after reconfiguration. Consider adding a reconfiguration listener if your application uses dynamic reconfiguration.
+
+## Troubleshooting
+
+### Filter not installing
+
+If you see errors during filter installation, ensure that:
+
+1. Log4j2 is actually on your classpath
+2. You're using Log4j2 (not Log4j 1.x or another logging implementation)
+3. The filter installation happens after Log4j2 initialization
+
+To verify Log4j2 is being used:
+```java
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.core.LoggerContext;
+
+try {
+    LoggerContext context = (LoggerContext) LogManager.getContext(false);
+    System.out.println("Using Log4j2: " + context.getClass().getName());
+} catch (ClassCastException e) {
+    System.out.println("NOT using Log4j2 Core");
+}
+```
+
+### Log levels not changing
+
+If log levels aren't being respected:
+
+1. Verify the config key exists in Reforge (default: `log-levels.default`)
+2. Check that it's of type `LOG_LEVEL_V2`
+3. Ensure the Reforge SDK is initialized and ready
+4. Check the SDK logs for any errors during config retrieval
+5. Verify the filter is still installed (it may have been removed by reconfiguration)
+
+### Existing Log4j2 configuration overriding dynamic levels
+
+The filter runs as part of Log4j2's filter chain. However, if you have:
+- Appender-level filters with thresholds
+- Very restrictive context-wide filters
+- Logger-level settings that are more restrictive
+
+These may still apply. The filter controls whether a log event is created at all, but downstream filters and appender settings can still block events.
+
+### Filter removed after reconfiguration
+
+If your application uses Log4j2's configuration file watching or programmatic reconfiguration, the filter will be removed. Options:
+
+1. **Disable automatic reconfiguration** if not needed
+2. **Add a reconfiguration listener** that reinstalls the filter
+3. **Install via configuration** (though this requires static SDK access)
+
+## Example Application
+
+```java
+package com.example;
+
+import com.reforge.sdk.Sdk;
+import com.reforge.sdk.Options;
+import com.reforge.sdk.log4j2.ReforgeLog4j2Filter;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+
+public class MyApplication {
+    private static final Logger log = LogManager.getLogger(MyApplication.class);
+
+    public static void main(String[] args) {
+        // Initialize Reforge SDK
+        Sdk sdk = new Sdk(new Options());
+
+        // Install Log4j2 integration
+        ReforgeLog4j2Filter.install(sdk.loggerClient());
+
+        log.trace("This is a trace message");  // Filtered if level > TRACE
+        log.debug("This is a debug message");  // Filtered if level > DEBUG
+        log.info("This is an info message");   // Filtered if level > INFO
+        log.warn("This is a warning");         // Filtered if level > WARN
+        log.error("This is an error");         // Filtered if level > ERROR
+        log.fatal("This is fatal");            // Filtered if level > FATAL
+    }
+}
+```
+
+## Differences from Logback Integration
+
+The Log4j2 integration differs from Logback in a few ways:
+
+| Feature | Log4j2 | Logback |
+|---------|--------|---------|
+| Filter type | AbstractFilter | TurboFilter |
+| Filter scope | LoggerContext-wide | Framework-wide |
+| Reconfiguration | Filter removed on reconfig | Filter persists |
+| FATAL level | Native support | Maps to ERROR |
+
+Both integrations provide the same dynamic log level functionality with similar performance characteristics.
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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>
+
+  <parent>
+    <groupId>com.reforge</groupId>
+    <artifactId>sdk-parent</artifactId>
+    <version>1.1.0</version>
+  </parent>
+
+  <artifactId>sdk-log4j2</artifactId>
+  <packaging>jar</packaging>
+  <name>Reforge SDK Log4j2 Integration</name>
+  <description>Log4j2 integration for Reforge SDK dynamic log level management</description>
+
+  <dependencies>
+    <!-- Reforge SDK -->
+    <dependency>
+      <groupId>com.reforge</groupId>
+      <artifactId>sdk</artifactId>
+      <version>${project.version}</version>
+    </dependency>
+
+    <!-- Log4j2 (provided scope - use customer's version) -->
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-api</artifactId>
+      <scope>provided</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>org.apache.logging.log4j</groupId>
+      <artifactId>log4j-core</artifactId>
+      <scope>provided</scope>
+    </dependency>
+
+    <!-- SLF4J API (provided scope - use customer's version) -->
+    <dependency>
+      <groupId>org.slf4j</groupId>
+      <artifactId>slf4j-api</artifactId>
+      <scope>provided</scope>
+    </dependency>
+
+    <!-- Test dependencies -->
+    <dependency>
+      <groupId>org.assertj</groupId>
+      <artifactId>assertj-core</artifactId>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter</artifactId>
+      <scope>test</scope>
+    </dependency>
+
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-core</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>
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+package com.reforge.sdk.log4j2;
+
+import com.reforge.sdk.LogLevel;
+import org.apache.logging.log4j.Level;
+
+class Log4jLevelMapper {
+
+  static Level toLog4jLevel(LogLevel reforgeLevel) {
+    switch (reforgeLevel) {
+      case FATAL:
+        return Level.FATAL;
+      case ERROR:
+        return Level.ERROR;
+      case WARN:
+        return Level.WARN;
+      case INFO:
+        return Level.INFO;
+      case DEBUG:
+        return Level.DEBUG;
+      case TRACE:
+        return Level.TRACE;
+      default:
+        return Level.DEBUG;
+    }
+  }
+}