AutoMDC: manage the SLF4J mapped diagnostic context using try-with-resources

AutoMDC.java

// This code has been placed in the public domain by the author.
//
// You may use, modify, and redistribute without restriction.
//
// Use of this software is on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
// CONDITIONS OF ANY KIND, either express or implied.

package com.kdgregory.example;

import java.util.HashSet;
import java.util.Set;

import org.slf4j.MDC;


/**
 *  This class leverages the try-with-resources feature of Java 1.7 and later to
 *  manage the SLF4J mapped diagnostic context.
 */
public final class AutoMDC
implements AutoCloseable
{
    private Set<String> keys;
    
    
    /**
     *  Default constructor; call the {@link #put} method to add keys and values.
     */
    public AutoMDC()
    {
        keys = new HashSet<>();
    }
    
    
    /**
     *  Convenience constructor, for when you have a single key/value pair.
     */
    public AutoMDC(String key, Object value)
    {
        this();
        put(key, value);
    }
    
    
    /**
     *  Adds a key/value pair to the MDC.
     */
    public AutoMDC put(String key, Object value)
    {
        keys.add(key);
        MDC.put(key, String.valueOf(value));
        return this;
    }
    

    @Override
    public void close() throws Exception
    {
        for (String key : keys)
        {
            MDC.remove(key);
        }
    }

}

logback.xml

<configuration debug="false">

    <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{ISO8601} %-5level [%thread] %logger{24} - %mdc - %msg%n</pattern>
        </encoder>
    </appender>

    <root level="warn">
        <appender-ref ref="CONSOLE" />
    </root>

    <logger name="com.kdgregory" level="debug"/>

</configuration>

Main.java

// This code has been placed in the public domain by the author.
//
// You may use, modify, and redistribute without restriction.
//
// Use of this software is on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
// CONDITIONS OF ANY KIND, either express or implied.

package com.kdgregory.example;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStreamWriter;
import java.nio.charset.StandardCharsets;

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

/**
 *  Uses the AutoMDC class to update the MDC.
 */
public class Main
{
    private static Logger logger = LoggerFactory.getLogger(Main.class);
    
    
    public static void main(String[] argv)
    throws Exception
    {        
        logger.info("program starting");
        
        File file = new File(argv[0]);
        
        try (AutoMDC mdc = new AutoMDC("outputFile", file.getAbsolutePath());
            FileOutputStream fos = new FileOutputStream(file);
                OutputStreamWriter osr = new OutputStreamWriter(fos, StandardCharsets.UTF_8);
                BufferedWriter out = new BufferedWriter(osr))
        {
            logger.info("starting to write");
            out.write("hello, world");
            out.newLine();
            logger.info("finished writing");
        }
        
        logger.info("program finished");
    }
}

pom.xml

<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/maven-v4_0_0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.kdgregory.example</groupId>
    <artifactId>automdc</artifactId>
    <version>1.0.0</version>
    <packaging>jar</packaging>

    <name>AutoMDC</name>

    <description>
        Example of using AutoCloseable to manage the MDC
    </description>


    <properties>
        <jdk.version>1.8</jdk.version>

        <!-- build configuration props, because Maven can't pick a sensible default -->
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>

        <logback.version>1.2.3</logback.version>

        <plugin.compiler.version>3.1</plugin.compiler.version>
        <plugin.shade.version>3.1.1</plugin.shade.version>
    </properties>


    <dependencies>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>${logback.version}</version>
        </dependency>
    </dependencies>


    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>${plugin.compiler.version}</version>
                <configuration>
                    <source>${jdk.version}</source>
                    <target>${jdk.version}</target>
                    <debug>true</debug>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>${plugin.shade.version}</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <createDependencyReducedPom>false</createDependencyReducedPom>
                            <transformers>
                                <transformer
                                    implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <mainClass>com.kdgregory.example.Main</mainClass>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

</project>

TradMain.java

// This code has been placed in the public domain by the author.
//
// You may use, modify, and redistribute without restriction.
//
// Use of this software is on an "AS IS" BASIS, WITHOUT WARRANTIES OR 
// CONDITIONS OF ANY KIND, either express or implied.

package com.kdgregory.example;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStreamWriter;
import java.nio.charset.StandardCharsets;

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


/**
 *  Demonstrates "traditional" use of the MDC.
 */
public class TradMain
{
    private static Logger logger = LoggerFactory.getLogger(TradMain.class);
    
    
    public static void main(String[] argv)
    throws Exception
    {        
        logger.info("program starting");
        
        File file = new File(argv[0]);
        
        MDC.put("outputFile", file.getAbsolutePath());
        try (FileOutputStream fos = new FileOutputStream(file);
                OutputStreamWriter osr = new OutputStreamWriter(fos, StandardCharsets.UTF_8);
                BufferedWriter out = new BufferedWriter(osr))
        {
            logger.info("starting to write");
            out.write("hello, world");
            out.newLine();
            logger.info("finished writing");
        }
        
        MDC.remove("outputFile");
        logger.info("program finished");
    }
}