摘要:

import org.apache.log4j.Logger;

public class MyClass {
  /*
   * Obtain a logger for a message category. In this case, the message category is
   * the fully qualified class name of MyClass.
   */
  private static final Logger logger = Logger.getLogger(MyClass.class.getName());
  ...
  public void myMethod() {
    ...
    if (logger.isDebugEnabled()) {
      logger.debug("Executing with parameters: " + param1 + ":" + param2);
    }
  }
}

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta./log4j/">
        
  <appender name="fileAppender" class="org.apache.log4j.FileAppender">
    <param name="File" value="log.txt"/>
    <param name="Append" value="true"/>
    <layout class="org.apache.log4j.PatternLayout">
      <param name="ConversionPattern" value="%d [%t] %p - %m%n"/>
    </layout>
  </appender>

  <category name="com.ambrosesoft.log.MyClass">
    <priority value="error"/>
    <appender-ref ref="fileAppender"/>
  </category>

  <root>
    <priority value="debug"/>
    <appender-ref ref="fileAppender"/>
  </root>

</log4j:configuration>

import org.apache.log4j.Logger;

public interface Loggers {
  Logger performance = Logger.getLogger("performance");
  Logger security = Logger.getLogger("security");
  Logger business = Logger.getLogger("business");
}
...
public class MyClass {
  ....
  if (Loggers.security.isWarnEnabled()) {
    Loggers.security.warn("Access denied: Username [" + userName + "] ...");
  }
  ...
}

import javax.servlet.Filter;
...
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import org.apache.log4j.MDC;

public class LoggerFilter implements Filter {
    
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        
        // Retrieves the session object from the current request.
        HttpSession session = ((HttpServletRequest)request).getSession();
        
        // Put the username into the diagnostic context.
        // Use %X{username} in the layout pattern to include this information.
        MDC.put("username", session.getAttribute("username"));
        
        // Continue processing the rest of the filter chain.
        chain.doFilter(request, response);
        
        // Remove the username from the diagnostic context.
        MDC.remove("username");
    }
    ...
}

import org.apache.log4j.Logger;
import java.lang.reflect.Field;

public aspect AutoTrace {

    private static final Logger logger = Logger.getLogger(AutoTrace.class);
    
    pointcut publicMethods() : execution(public * com.ambrosesoft..*(..));

    pointcut loggableCalls() : publicMethods();
    
    /**
     * Inspect the class and find its logger object. If none is found, use
     * the one defined here.
     */
    private Logger getLogger(org.aspectj.lang.JoinPoint joinPoint) {
        try {
            /*
             * Try to discover the logger object. 
             * The logger object must be a static field called logger.
             */
            Class declaringType = joinPoint.getSignature().getDeclaringType();
            Field loggerField = declaringType.getField("logger");
            loggerField.setAccessible(true);
            return (Logger)loggerField.get(null);
        } catch(NoSuchFieldException e) {
            /*
             * Cannot find a logger object, use the internal one.
             */
            return logger;
        } catch(Exception e) {
            throw new RuntimeException(e);
        }
    }
    
    /**
     * An aspect to log method entry.
     */
    before() : loggableCalls(){
        getLogger(thisJoinPoint).debug("Entering.." + thisJoinPoint.getSignature().toString());
    }
      
    /**
     * An aspect to log method exit.
     */
    after() : loggableCalls(){
        getLogger(thisJoinPoint).debug("Exiting.." + thisJoinPoint.getSignature().toString());
    }
} 

*
 * Configure Log4J library and periodically monitor log4j.xml for any update.
 */
DOMConfigurator.configureAndWatch("/apps/config/log4j.xml");

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">

<log4j:configuration xmlns:log4j="http://jakarta./log4j/">
        
  <appender name="fileAppender" class="org.apache.log4j.DailyRollingFileAppender">
    <param name="File" value="log.txt"/>
    <param name="Append" value="true"/>
    <param name="DatePattern" value="‘.‘yyyy-MM-dd"/>
    <layout class="org.apache.log4j.PatternLayout">
      <param name="ConversionPattern" value="%d [%t] %p - %m%n"/>
    </layout>
  </appender>
...
</log4j:configuration>