如何将log4j2 FileAppender与SLF4J API一起使用

Question

我一直在尝试遵循这个网站和其他网站上的食谱，了解如何将log4j2 FileAppender实例添加到使用SLF4J API进行整体日志记录的类中，但我运气不佳。有人能告诉我下面的代码哪里出错了吗？

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.util.List;

import org.apache.commons.io.FileUtils;
import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.core.Layout;
import org.apache.logging.log4j.core.LoggerContext;
import org.apache.logging.log4j.core.appender.FileAppender;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.LoggerConfig;
import org.apache.logging.log4j.core.layout.PatternLayout;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class FileAppenderTest {

    private static final Logger log = LoggerFactory.getLogger(FileAppenderTest.class);

    private final Layout<?> taskLogLayout = PatternLayout.newBuilder()
        .withPattern("%d %-5p [%t:%C{1}.%M] %m%n")
        .build();

    @Test
    public void testFileAppender() throws IOException {

        File appenderFile = new File("build/test", "file-appender.log");

        FileAppender taskLog = FileAppender.newBuilder()
            .withFileName(appenderFile.getAbsolutePath())
            .setName("file-appender.log")
            .setLayout(taskLogLayout)
            .build();
        taskLog.start();

        LoggerContext ctx = (LoggerContext) LogManager.getContext(false);
        Configuration c = ctx.getConfiguration();
        LoggerConfig lc = c.getLoggerConfig("");
        lc.addAppender(taskLog, Level.ALL, null);

        log.info("Here is a test message with INFO level");
        log.warn("Here is a test message with WARN level");

        lc.removeAppender("file-appender.log");

        assertTrue(appenderFile.exists());

        List<String> logLines = FileUtils.readLines(appenderFile, (Charset) null);
        assertEquals(2, logLines.size());

    }

}

assertTrue语句通过，因此文件由FileAppender创建，但assertEquals失败，因为日志线的长度为零（即日志文件没有内容）。

有什么想法吗？

Answer 1

发现问题：

在上面的代码中，请注意，记录器是在应用任何日志配置设置之前从LoggerFactory获得的。这会导致记录器出现默认错误级别。因此，即使APPENDER具有一定级别的信息，记录器也具有一定级别的错误，并且在信息和警告消息到达APPENDER之前拒绝它们！

以下代码将通过所有测试。请注意，记录器不再是静态成员，配置设置为在获取记录器之前具有任何级别。

package gov.nasa.ziggy.worker;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;

import java.io.File;
import java.io.IOException;
import java.nio.charset.Charset;
import java.util.List;

import org.apache.commons.io.FileUtils;
import org.apache.logging.log4j.Level;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.core.Layout;
import org.apache.logging.log4j.core.LoggerContext;
import org.apache.logging.log4j.core.appender.FileAppender;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.LoggerConfig;
import org.apache.logging.log4j.core.layout.PatternLayout;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class FileAppenderTest {

    private final Layout<?> taskLogLayout = PatternLayout.newBuilder()
        .withPattern("%d %-5p [%t:%C{1}.%M] %m%n")
        .build();

    @Test
    public void testFileAppender() throws IOException {

        LoggerContext ctx = (LoggerContext) LogManager.getContext(false);
        Configuration c = ctx.getConfiguration();
        LoggerConfig lc = c.getLoggerConfig("");
        lc.setLevel(Level.ALL);

        Logger log = LoggerFactory.getLogger(FileAppenderTest.class);
        File appenderFile = new File("build/test", "file-appender.log");

        FileAppender taskLog = FileAppender.newBuilder()
            .withFileName(appenderFile.getAbsolutePath())
            .setName("file-appender.log")
            .setLayout(taskLogLayout)
            .build();
        taskLog.start();

        lc.addAppender(taskLog, Level.ALL, null);

        log.info("Here is a test message with INFO level");
        log.warn("Here is a test message with WARN level");

        lc.removeAppender("file-appender.log");

        assertTrue(appenderFile.exists());

        List<String> logLines = FileUtils.readLines(appenderFile, (Charset) null);
        assertEquals(2, logLines.size());

    }

}