覆盖运行时 SLF4J 绑定以进行测试

Question

我正在写一个包。我需要slf4j-log4j12用于运行时的特定附加程序。但是对于测试，我只需要一个slf4j-simple绑定。所以，我的pom.xml样子是这样的：

<?xml version="1.0" encoding="UTF-8"?>
<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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <properties>
        <maven.compiler.target>1.8</maven.compiler.target>
        <maven.compiler.source>1.8</maven.compiler.source>
    </properties>

    <groupId>com.bharani</groupId>
    <artifactId>LoggingDemo</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <!-- Direct dependencies -->
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.25</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-log4j12 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.25</version>
            <scope>runtime</scope>
        </dependency>

        <!-- Test dependencies -->
        <!-- https://mvnrepository.com/artifact/junit/junit -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.assertj/assertj-core -->
        <dependency>
            <groupId>org.assertj</groupId>
            <artifactId>assertj-core</artifactId>
            <version>3.8.0</version>
            <scope>test</scope>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-simple -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.25</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

</project>

当我运行我的程序时，我得到了预期的log4j日志。但是当我运行测试时，我得到：

SLF4J: Class path contains multiple SLF4J bindings.
SLF4J: Found binding in [jar:file:/Users/bharani/.m2/repository/org/slf4j/slf4j-log4j12/1.7.25/slf4j-log4j12-1.7.25.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: Found binding in [jar:file:/Users/bharani/.m2/repository/org/slf4j/slf4j-simple/1.7.25/slf4j-simple-1.7.25.jar!/org/slf4j/impl/StaticLoggerBinder.class]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual binding is of type [org.slf4j.impl.Log4jLoggerFactory]

...而且我没有在控制台中看到预期的未slf4j-simple绑定日志。

我该如何解决？如何让runtime依赖slf4j-log4j12远离测试？

谢谢。

Answer 1

问题是，范围的依赖runtime是还包括在测试classpath中SLF4J结束有两个绑定，并有选择其中之一（结合它选择可能是随机的，它发生在你的情况下拿起log4j的）。

一个简单的解决方案是从 Surefire 插件的类路径中删除 log4j 绑定：

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-surefire-plugin</artifactId>
      <version>2.20.1</version>
      <configuration>
        <classpathDependencyExcludes>
          <classpathDependencyExcludes>org.slf4j:slf4j-log4j12</classpathDependencyExcludes>
        </classpathDependencyExcludes>
      </configuration>
    </plugin>
  </plugins>
</build>

更多信息在http://maven.apache.org/surefire/maven-surefire-plugin/examples/configuring-classpath.html。