1. 简介

        在Logback中，推荐使用配置文件（如logback.xml或logback-spring.xml）来设置日志记录的行为。但在实际应用中，会有动态配置logback的需求。此时可通过编程的方式直接操作LoggerContext以及相关的Logger、Appender、Encoder等组件来实现。

2. 代码示例

// step1: 获取LoggerContext的实例,要求其具体实现为logback（通过SPI指定）
LoggerContext context = (LoggerContext) LoggerFactory.getILoggerFactory();// step2: 进行设置
try {// step2.1: 创建RollingFileAppender并进行配置RollingFileAppender<ILoggingEvent> fileAppender = new RollingFileAppender<>();fileAppender.setContext(context);fileAppender.setFile("/logs/service.log");// step2.2: 创建滚动策略TimeBasedRollingPolicy<ILoggingEvent> rollingPolicy = new TimeBasedRollingPolicy<>();rollingPolicy.setContext(context);rollingPolicy.setFileNamePattern("/logs/service.%d{yyyy-MM-dd}.log");rollingPolicy.setMaxHistory(30);fileAppender.setRollingPolicy(rollingPolicy);rollingPolicy.setParent(fileAppender);  // 该条语句非常关键rollingPolicy.start();// step2.3: 创建EncoderPatternLayoutEncoder encoder = new PatternLayoutEncoder();encoder.setContext(context);encoder.setPattern("%d{yyyy-MM-dd HH:mm:ss} [%thread] %-5level %logger{36} - %msg%n");encoder.start();fileAppender.setEncoder(encoder);// step2.4: 创建Filter，设定只输出INFO和ERROR级别LevelFilter infoFilter = new LevelFilter();infoFilter.setContext(context);infoFilter.setLevel(Level.INFO);infoFilter.setOnMatch(FilterReply.ACCEPT);infoFilter.setOnMismatch(FilterReply.NEUTRAL);infoFilter.start();LevelFilter errorFilter = new LevelFilter();errorFilter.setContext(context);errorFilter.setLevel(Level.ERROR);errorFilter.setOnMatch(FilterReply.ACCEPT);errorFilter.setOnMismatch(FilterReply.DENY);errorFilter.start();fileAppender.addFilter(infoFilter);fileAppender.addFilter(errorFilter);// step2.5: 启动FileAppenderfileAppender.start();// step2.6: 配置ROOT的日志级别以及Appendercontext.getLogger(Logger.ROOT_LOGGER_NAME).addAppender(fileAppender);context.getLogger(Logger.ROOT_LOGGER_NAME).setLevel(Level.INFO);
} catch (Exception e) {throw new RuntimeException(e);
}