避免此警告的一种简单方法是将以下运行时依赖项添加到项目的 POM
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.7.2</version>
<scope>runtime</scope>
</dependency>
这将提供一个简单的日志实现,它将打印您的 INFO 级别语句。您将很快超越此解决方案,但它允许您有时间研究您的代码最终将使用的日志记录框架。
SLF4J是一个框架,旨在隐藏日志记录的实际实现细节。例如,在运行时,您可以决定使用log4j、commons logging、Java logging或logback。
更新 1:如何重现问题
以下 Java 项目重现了您的问题:
|-- pom.xml
`-- src
`-- main
`-- java
`-- HelloWorld.java
从 Maven 运行程序如下:
$ mvn exec:java -Dexec.mainClass=HelloWorld
..
..
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
一旦将缺少的依赖项添加到 POM 中,您的程序就会有一个日志记录实现,它可以使用它来发出它的日志记录语句,如下所示:
$ mvn exec:java -Dexec.mainClass=HelloWorld
..
..
[HelloWorld.main()] INFO HelloWorld - Java says: Hello world
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
pom.xml
<project>
<modelVersion>4.0.0</modelVersion>
<groupId>com.myspotontheweb.demo</groupId>
<artifactId>my-project</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.2</version>
</dependency>
</dependencies>
</project>
HelloWorld.java
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class HelloWorld {
Logger log = LoggerFactory.getLogger(HelloWorld.class);
public String speak(String speech) {
log.info("Java says: {}", speech);
return speech;
}
public static void main(String[] args) {
HelloWorld hello = new HelloWorld();
hello.speak("Hello world");
}
}
更新 2:如何创建可执行 jar
如果您将 Maven 配置为创建可执行 jar,那么它将自动使用引用 POM 文件中列出的依赖项的类路径打包 jar。
$ mvn clean package
$ java -jar target/my-project-1.0-SNAPSHOT.jar
[main] INFO HelloWorld - Java says: Hello world
pom.xml
<project>
<modelVersion>4.0.0</modelVersion>
<groupId>com.myspotontheweb.demo</groupId>
<artifactId>my-project</artifactId>
<version>1.0-SNAPSHOT</version>
<dependencies>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.2</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.7.2</version>
<scope>runtime</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<classpathPrefix>lib/</classpathPrefix>
<mainClass>HelloWorld</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<executions>
<execution>
<id>copy</id>
<phase>package</phase>
<goals>
<goal>copy-dependencies</goal>
</goals>
<configuration>
<outputDirectory>${project.build.directory}/lib</outputDirectory>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>