如何使用log4j获得SLF4J"Hello World"？

Question

SLF4J的"Hello World"示例对我不起作用.我想这是因为我将slf4j-log4添加到了我的类路径中.我应该直接配置log4j以使hello world工作吗？

log4j:WARN No appenders could be found for logger (HelloWorld).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

更新:我添加了log4j初始化,它仍然无法正常工作:

public static void main(String[] params) {
        org.apache.log4j.Logger.getRootLogger().addAppender(new ConsoleAppender());
        Logger logger = org.slf4j.LoggerFactory.getLogger(TestBase.class);
        logger.info("Hello World");
    }

我得到了:

log4j:ERROR No output stream or file set for the appender named [null].

Answer 1

如果要使用slf4j simple,则需要jar在类路径中使用以下文件:

• SLF4J-API-1.6.1.jar
• SLF4J-简单1.6.1.jar

如果你想使用slf4j和log4j,你需要jar在类路径上这些文件:

• SLF4J-API-1.6.1.jar
• SLF4J-log4j12-1.6.1.jar
• log4j的-1.2.16.jar

不多也不少.使用slf4j simple,您将获得INFO级别或更高级别的基本日志记录.使用时log4j,必须相应地进行配置.

Answer 2

以下是一个例子.您可以在此处查看详细信息http://jkssweetlife.com/configure-slf4j-working-various-logging-frameworks/并下载完整代码.

• 如果您使用maven,请将以下依赖项添加到您的pom,否则,只需下载jar文件并放入类路径

  <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-api</artifactId>
      <version>1.7.7</version>
  </dependency>
  
  <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>slf4j-log4j12</artifactId>
      <version>1.7.7</version>
  </dependency>
  

• 配置log4j.properties

  log4j.rootLogger=TRACE, stdout
  log4j.appender.stdout=org.apache.log4j.ConsoleAppender
  log4j.appender.stdout.Target=System.out
  log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
  log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd'T'HH:mm:ss.SSS} %-5p [%c] - %m%n
  

• Java示例

  public class Slf4jExample {
      public static void main(String[] args) {
  
          Logger logger = LoggerFactory.getLogger(Slf4jExample.class);
  
          final String message = "Hello logging!";
          logger.trace(message);
          logger.debug(message);
          logger.info(message);
          logger.warn(message);
          logger.error(message);
      }
  }
  

Answer 3

you need to add 3 dependency ( API+ API implementation + log4j dependency) 
Add also this 
<dependency>
    <groupId>org.apache.logging.log4j</groupId>
    <artifactId>log4j-core</artifactId>
    <version>2.5</version>
</dependency>

# And to see log in command line , set log4j.properties 

# Root logger option
log4j.rootLogger=INFO, file, stdout
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target=System.out
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n

#And to see log in file  , set log4j.properties 
# Direct log messages to a log file
log4j.appender.file=org.apache.log4j.RollingFileAppender
log4j.appender.file.File=./logs/logging.log
log4j.appender.file.MaxFileSize=10MB
log4j.appender.file.MaxBackupIndex=10
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n