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tessl/maven-org-slf4j--log4j-over-slf4j

Log4j 1.x API compatibility layer that implements Apache Log4j API over SLF4J for seamless migration

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tessl
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mavenpkg:maven/org.slf4j/log4j-over-slf4j@2.0.x

To install, run

npx @tessl/cli install tessl/maven-org-slf4j--log4j-over-slf4j@2.0.0

index.mddocs/

Log4j-over-SLF4J

Log4j-over-SLF4J is a compatibility layer that implements the Apache Log4j 1.x API over SLF4J (Simple Logging Facade for Java). It allows applications originally written to use Log4j 1.x to seamlessly work with SLF4J-based logging implementations without requiring code changes. The library provides drop-in replacement classes for all major Log4j components, delegating their functionality to corresponding SLF4J components.

Package Information

  • Package Name: log4j-over-slf4j
  • Package Type: maven
  • Language: Java
  • Group ID: org.slf4j
  • Artifact ID: log4j-over-slf4j
  • Installation: Add to Maven dependencies: 
    <dependency>
  <groupId>org.slf4j</groupId>
  <artifactId>log4j-over-slf4j</artifactId>
  <version>2.0.17</version>
</dependency>

Core Imports

import org.apache.log4j.Logger;
import org.apache.log4j.LogManager;
import org.apache.log4j.Level;

For diagnostic contexts:

import org.apache.log4j.MDC;
import org.apache.log4j.NDC;

Basic Usage

import org.apache.log4j.Logger;
import org.apache.log4j.Level;

// Get a logger instance
Logger logger = Logger.getLogger(MyClass.class);

// Or get by name
Logger namedLogger = Logger.getLogger("com.example.MyLogger");

// Log at different levels
logger.debug("Debug message");
logger.info("Info message"); 
logger.warn("Warning message");
logger.error("Error message");
logger.fatal("Fatal message");

// Log with exceptions
try {
    // some operation
} catch (Exception e) {
    logger.error("Operation failed", e);
}

// Check if level is enabled
if (logger.isDebugEnabled()) {
    logger.debug("Expensive debug operation: " + computeExpensiveData());
}

Architecture

Log4j-over-SLF4J is designed as a bridge between Log4j 1.x API and SLF4J implementations:

  • API Compatibility: Provides complete Log4j 1.x API compatibility without changing application code
  • SLF4J Delegation: All logging operations delegate to underlying SLF4J logger instances
  • Configuration Passthrough: Configuration is handled by the SLF4J implementation (e.g., Logback)
  • No-op Implementations: Configuration classes like PropertyConfigurator are no-op since configuration is handled by SLF4J
  • Context Bridging: MDC and NDC implementations use SLF4J's MDC mechanism

Capabilities

Core Logging

Primary logging functionality including logger creation, level checking, and message logging at all standard Log4j levels (TRACE, DEBUG, INFO, WARN, ERROR, FATAL).

// Logger creation
public static Logger getLogger(String name);
public static Logger getLogger(Class<?> clazz);
public static Logger getRootLogger();

// Level checking
public boolean isDebugEnabled();
public boolean isInfoEnabled();
public boolean isWarnEnabled();
public boolean isErrorEnabled();

// Basic logging methods
public void debug(Object message);
public void info(Object message);
public void warn(Object message);
public void error(Object message);
public void fatal(Object message);

Core Logging

Level Management

Level and priority system providing standard Log4j levels (OFF, FATAL, ERROR, WARN, INFO, DEBUG, TRACE, ALL) with conversion utilities and level comparison methods.

// Standard levels
public static final Level OFF;
public static final Level FATAL;
public static final Level ERROR;
public static final Level WARN;
public static final Level INFO;
public static final Level DEBUG;
public static final Level TRACE;
public static final Level ALL;

// Level conversion
public static Level toLevel(String sArg);
public static Level toLevel(int val);
public static Level toLevel(String sArg, Level defaultLevel);

Level Management

Diagnostic Contexts

Mapped Diagnostic Context (MDC) and Nested Diagnostic Context (NDC) for adding contextual information to log messages across thread boundaries.

// MDC operations
public static void put(String key, String value);
public static Object get(String key);
public static void remove(String key);
public static void clear();

// NDC operations  
public static void push(String message);
public static String pop();
public static String peek();
public static void clear();
public static int getDepth();

Diagnostic Contexts

Configuration

Configuration utilities providing Log4j 1.x API compatibility for basic and property-based configuration (implemented as no-op since configuration is handled by SLF4J).

// Basic configuration
public static void configure();
public static void configure(Appender appender);

// Property configuration
public static void configure(Properties properties);
public static void configure(String configFilename);
public static void configureAndWatch(String configFilename);

Configuration

Appenders and Layouts

Appender interfaces and skeleton implementations for output destinations, plus layout classes for message formatting (mostly no-op implementations since output handling is managed by SLF4J).

// Appender interface
public interface Appender {
    void doAppend(LoggingEvent event);
    String getName();
    void setName(String name);
    boolean requiresLayout();
    void close();
}

// Common appenders
public class ConsoleAppender extends WriterAppender;
public class FileAppender extends WriterAppender;
public class RollingFileAppender extends FileAppender;

Appenders and Layouts

Types

// Core logger hierarchy
public class Logger extends Category {
    protected Logger(String name);
}

public class Category {
    protected final String name;
    protected org.slf4j.Logger slf4jLogger;
}

// Level and Priority
public class Level extends Priority implements Serializable {
    protected Level(int level, String levelStr, int syslogEquivalent);
}

public class Priority {
    transient int level;
    transient String levelStr;
    transient int syslogEquivalent;
}

// Service Provider Interfaces
public interface LoggerFactory {
    public Logger makeNewLoggerInstance(String name);
}

public interface Appender {
    void doAppend(LoggingEvent event);
    String getName();
    void setName(String name);
    Layout getLayout();
    void setLayout(Layout layout);
    boolean requiresLayout();
    void close();
}