Question

来自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，但仍然无效：

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

如果您想使用slf4j simple，则需要在类路径中使用这些jar个文件：

SLF4J-API-1.6.1.jar
slf4j-simple-1.6.1.jar

如果您想使用slf4j和log4j，则需要在类路径中使用这些jar个文件：

SLF4J-API-1.6.1.jar
slf4j-log4j12-1.6.1.jar
的log4j-1.2.16.jar

不多也不少。使用slf4j simple，您将获得INFO级或更高级别的基本日志记录。使用log4j，您必须configure it accordingly。

Answer 2

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

如果您正在使用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

Answer 4

我遇到了同样的问题。当直接使用log4j api时，我从log4j.properties文件中调用了我自己的自定义记录器。如果您正在使用slf4j api调用，那么您可能正在使用默认的根记录器，因此您必须将其配置为与log4j.properties中的appender关联：


    # Set root logger level to DEBUG and its only appender to A1.
    log4j.rootLogger=DEBUG, A1

    # A1 is set to be a ConsoleAppender.
    log4j.appender.A1=org.apache.log4j.ConsoleAppender

Answer 5

下面是一个使用slf4j作为幕墙，并在后端使用log4j的工作示例：

pom.xml

/products/${node.category_id}?diameter=15,25&length=100,200

src / main / resources / log4j.properties

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>xxx</groupId>
    <artifactId>xxx</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.30</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-log4j12 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.30</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-core -->
        <dependency>
            <groupId>org.apache.logging.log4j</groupId>
            <artifactId>log4j-core</artifactId>
            <version>2.13.3</version>
        </dependency>
    </dependencies>
</project>

src / main / java / Main.java

# Root logger option
log4j.rootLogger=DEBUG, stdout

# Direct log messages to 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

如何使用log4j获得SLF4J“Hello World”？

5 个答案: