Slf4j+Logback配置文件变量使用小记

时间:2022-04-27
本文章向大家介绍Slf4j+Logback配置文件变量使用小记,主要内容包括测试准备、方式一:变量替换、测试二(多线程)、方式二:MDC、测试二(多线程)、总结、基本概念、基础应用、原理机制和需要注意的事项等,并结合实例形式分析了其使用技巧,希望通过本文能帮助到大家理解应用这部分内容。

项目中须要根据不同的模块,产生出不同的日志文件名,使用的是同一logback.xml配置文件,这里简单调研,说明两种实现方式,以及两种实现方式的区别。

测试准备

建立一个maven项目,并添加slf4j-api, logback-core, logback-classic 依赖。

    <dependencies>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.13</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-core</artifactId>
            <version>1.1.3</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.1.3</version>
        </dependency>
    </dependencies>

方式一:变量替换

详细信息参考:https://logback.qos.ch/manual/configuration.html#variableSubstitution

测试一(单线程)

logback.xml

<?xml version="1.0" encoding="UTF-8"?>
<configuration>

    <appender name="FILE"
              class="ch.qos.logback.core.FileAppender">
        <File>test-logger-${test-variable}.log</File>
        <Append>true</Append>
        <layout class="ch.qos.logback.classic.PatternLayout">
            <Pattern>%date %level [%thread] %logger{10} [%file:%line] %msg%n
            </Pattern>
        </layout>
    </appender>

    <root level="debug">
        <appender-ref ref="FILE" />
    </root>
</configuration>

测试代码

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class LoggerJVMParamTest {

    private static final Logger LOG = LoggerFactory.getLogger(LoggerJVMParamTest.class);

    public void printLog() {
        LOG.info("This is test log.");
    }

    public static void main(String[] args) {

        LoggerJVMParamTest test = new LoggerJVMParamTest();
        test.printLog();

        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

执行程序时加入jvm参数: -Dtest-variable="PROG"

执行结果及说明

生成了test-logger-PROG.log文件

2017-08-02 17:06:29,794 INFO [main] c.s.t.l.LoggerJVMParamTest [LoggerJVMParamTest.java:16] This is test log.

logback 中可以通过jvm参数传递变量来指定文件名, 当然变量的传递方式还有多种方式,这里不展开,可以参考https://logback.qos.ch/manual/configuration.html#variableSubstitution

测试二(多线程)

再看看在多线程环境中是否也都有效,logback.xml同测试一

测试代码

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.MDC;

public class LoggerJVMParamMultiThreadsTest {

    private static final Logger LOG = LoggerFactory.getLogger(LoggerJVMParamMultiThreadsTest.class);

    public void printLog() {
        LOG.info("This is test log.");
    }

    public static void main(String[] args) {

        LoggerJVMParamMultiThreadsTest test = new LoggerJVMParamMultiThreadsTest();


        Thread subThd1 = new Thread(new Runnable() {
            public void run() {
                LOG.info("This is subThd1 log");
            }
        });
        subThd1.start();

        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        test.printLog();

        Thread subThd2 = new Thread(new Runnable() {
            public void run() {
                LOG.info("This is subThd2 log");
            }
        });
        subThd2.start();

        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

执行程序时加入jvm参数: -Dtest-variable="PROG"

执行结果及说明

生成了test-logger-PROG.log文件

2017-08-02 17:26:01,786 INFO [Thread-0] c.s.t.l.LoggerJVMParamMultiThreadsTest [LoggerJVMParamMultiThreadsTest.java:27] This is subThd1 log
2017-08-02 17:26:06,791 INFO [main] c.s.t.l.LoggerJVMParamMultiThreadsTest [LoggerJVMParamMultiThreadsTest.java:17] This is test log.
2017-08-02 17:26:06,791 INFO [Thread-1] c.s.t.l.LoggerJVMParamMultiThreadsTest [LoggerJVMParamMultiThreadsTest.java:42] This is subThd2 log

方式二:MDC

详细信息参考:https://logback.qos.ch/manual/mdc.html

测试1(单线程)

logback.xml

<?xml version="1.0" encoding="UTF-8"?>
<configuration>

    <appender name="FILE_MDC" class="ch.qos.logback.classic.sift.SiftingAppender">
        <discriminator>
            <Key>test-variable</Key>
            <DefaultValue>default</DefaultValue>
        </discriminator>
        <sift>
            <appender name="FILE"
                      class="ch.qos.logback.core.FileAppender">
                <File>test-logger-${test-variable}.log</File>
                <Append>true</Append>
                <layout class="ch.qos.logback.classic.PatternLayout">
                    <Pattern>%date %level [%thread] %logger{10} [%file:%line] %msg%n</Pattern>
                </layout>
            </appender>
        </sift>
    </appender>

    <root level="debug">
        <appender-ref ref="FILE_MDC" />
    </root>

</configuration>

测试代码

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.MDC;

public class LoggerConfVariablesTest {

    private static final Logger LOG = LoggerFactory.getLogger(LoggerConfVariablesTest.class);

    public void printLog() {
        LOG.info("This is test log.");
    }

    public static void main(String[] args) {

        MDC.put("test-variable", "PROG");

        LoggerConfVariablesTest test = new LoggerConfVariablesTest();
        test.printLog();

        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

执行结果及说明

执行代码,生成日志文件:test-logger-PROG.log

内容:

2017-08-02 13:44:20,779 INFO [main] c.s.t.l.LoggerConfVariablesTest [LoggerConfVariablesTest.java:17] This is test log.

先看下ch.qos.logback.classic.sift.SiftingAppender类的说明:

This appender can contains other appenders which it can build dynamically depending on MDC values. The built appender is specified as part of a configuration file.

就是说SiftingAppender类可以根据MDC的值动态的构建其他的appender,由discriminator来指定MDC的Key和默认值。

根据https://logback.qos.ch/manual/mdc.html中的说明:

  MDC operations such as put() and get() affect only the MDC of the current thread, and the children of the current thread. The MDC in other threads remain unaffected.

MDC put(), get()会影响当前线程和子线程的MDC值,但是不会响应其他线程。再考虑上面的测试,那么其他线程应该是拿不到MDC test-variable的值的,打印的日志信息应该是不会输出到test-logger-PROG.log日志文件中去的,那它会输出到哪里呢? 接下来继续测试。

测试二(多线程)

logback.xml配置同测试一

测试代码

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.MDC;

public class LoggerConfVariablesTest {

    private static final Logger LOG = LoggerFactory.getLogger(LoggerConfVariablesTest.class);

    public void printLog() {
        LOG.info("This is test log.");
    }

    public static void main(String[] args) {



        LoggerConfVariablesTest test = new LoggerConfVariablesTest();


        Thread subThd1 = new Thread(new Runnable() {
            public void run() {
                MDC.put("test-variable", "PROG");
                LOG.info("This is subThd1 log");
            }
        });
        subThd1.start();

        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        test.printLog();

        Thread subThd2 = new Thread(new Runnable() {
            public void run() {
                LOG.info("This is subThd2 log");
            }
        });
        subThd2.start();

        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

执行结果及说明

生成了两个日志文件

test-logger-PROG.log

2017-08-02 16:45:22,798 INFO [Thread-0] c.s.t.l.LoggerConfVariablesTest [LoggerConfVariablesTest.java:30] This is subThd1 log

 test-logger-default.log

2017-08-02 16:45:27,790 INFO [main] c.s.t.l.LoggerConfVariablesTest [LoggerConfVariablesTest.java:17] This is test log.
2017-08-02 16:45:27,790 INFO [Thread-1] c.s.t.l.LoggerConfVariablesTest [LoggerConfVariablesTest.java:45] This is subThd2 log

可以知道

MDC.put("test-variable", "PROG"); 仅在subThd1中生效,其的父线程和兄弟线程取不到PROG这个值所以使用了默认值“default”。

总结

根据测试通过JVM变量方式来设置日志文件名,这个方式适用于单线程和多线程环境,但是MDC不适用多线程环境,特别是当MDC.put()方法的调用是非主线程的情况,比如javaEE项目就不适合这么做。根据对MDC的了解,MDC主要适用于须要在同一个进程中对不同的线程输出不同的日志格式,或输出到不同的文件这种场景,比如web项目,针对不同的用户请求,在日志中加入用户的信息,或者是不同的任务日志输出到不同的文件。

而对于须要将不同模块进程的日志输出到不同的文件,共用logback.xml, 则可以使用jvm参数传递变量的方式。