logback 之 创建 RollingFileAppender

最近有需求要将context信息写入文件，以备后续数据分析。本想直接同步写入文件了事，但是logback针对日志的输出性能尤佳，且为异步写入。既然logback封装如此完美，何不直接使用？

动态创建Logger及其appender。代码如下：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import ch.qos.logback.classic.Level;
import ch.qos.logback.classic.LoggerContext;
import ch.qos.logback.classic.encoder.PatternLayoutEncoder;
import ch.qos.logback.classic.spi.ILoggingEvent;
import ch.qos.logback.core.rolling.RollingFileAppender;
import ch.qos.logback.core.rolling.TimeBasedRollingPolicy;
 
        Logger logger = LoggerFactory.getLogger(loggerName);
        LoggerContext loggerContext = (LoggerContext) LoggerFactory.getILoggerFactory();
        
        ch.qos.logback.classic.Logger newLogger = (ch.qos.logback.classic.Logger)logger;
        //Remove all previously added appenders from this logger instance.
        newLogger.detachAndStopAllAppenders();
        
        //define appender
        RollingFileAppender<ILoggingEvent> appender = new RollingFileAppender<ILoggingEvent>();
        
        //policy
        TimeBasedRollingPolicy<ILoggingEvent> policy = new TimeBasedRollingPolicy<ILoggingEvent>();
        policy.setContext(loggerContext);
        policy.setMaxHistory(5);
        policy.setFileNamePattern("/home/lionbule/%d{yyyy-MM-dd}.log");
        policy.setParent(appender);
        policy.start();
        
        //encoder
        PatternLayoutEncoder encoder = new PatternLayoutEncoder();
        encoder.setContext(loggerContext);
        encoder.setPattern("%message%n");
        encoder.start();
        
        //start appender
        appender.setRollingPolicy(policy);
        appender.setContext(loggerContext);
        appender.setEncoder(encoder);
        appender.setPrudent(true); //support that multiple JVMs can safely write to the same file.
        appender.start();
        
        newLogger.addAppender(appender);
        
        //setup level
        newLogger.setLevel(Level.WARN);
        //remove the appenders that inherited 'ROOT'.
        newLogger.setAdditive(false);

上述代码为草稿，具体使用细节，则根据自己的需求调整。 

要点总结：

1. 成功创建appender的关键在于，要实例化一个appender，然后set policy/encoder/&others...

    最后再start appender。

    并且在创建policy时，一定要记住set当前实例化的appender。

    具体步骤看上述demo。