log4j2或者logback配置模版实现灵活输出服务名

介绍

在我们使用log4j2或者logback打印日志时，输出的内容中通常是一定要加上服务名的。以log4j2为例：

<Console name="Console" target="SYSTEM_OUT">
    
    <PatternLayout pattern="server-case %d{yyyy-MM-dd HH:mm:ss} %5p %c{1}:%L - %m%n"/>
Console>

服务名为server-case，输出的内容为

server-case 2023-09-15 17:44:38  INFO ServerCaseApplication:648 - No active profile set, falling back to default profiles: default
server-case 2023-09-15 17:44:39  INFO TomcatWebServer:108 - Tomcat initialized with port(s): 7081 (http)
server-case 2023-09-15 17:44:39  INFO Http11NioProtocol:173 - Initializing ProtocolHandler ["http-nio-7081"]
server-case 2023-09-15 17:44:39  INFO StandardService:173 - Starting service [Tomcat]
...

但是有种情况，有的项目要部署在甲方内网或者连接甲方的资源。项目是同一套代码，但要服务于不同的甲方，所以一个项目会有不同的服务名的情况。

这样的话，服务名就不能写死，要根据不同的服务名来输出。

问题

有的人可能会想到直接设置一个对象实现EnvironmentAware接口中的setEnvironment(Environment environment)，来获取environment来获取spring.application.name

但这样有问题，设置的这个对象是要在spring上下文中进行加载后才能获得environment，所以在这个对象加载之前的日志输出还是拿不到environment的

@Component
public class Test implements EnvironmentAware {
    
    private Environment environment;
    
    @Override
    public void setEnvironment(final Environment environment) {
        this.environment = environment;
        System.setProperty("applicationName", Objects.requireNonNull(environment.getProperty("spring.application.name")));
    }
}

<Console name="Console" target="SYSTEM_OUT">
    
    <PatternLayout pattern="${sys:applicationName} %d{yyyy-MM-dd HH:mm:ss} %5p %c{1}:%L - %m%n"/>
Console>

${sys:applicationName} 2023-09-18 10:18:34  INFO ServerCaseApplication:55 - Starting ServerCaseApplication on lukuan with PID 21472 (D:\idea_work_my\gitee\cook-frame\server\server-case\target\classes started by lukuan in D:\idea_work_my\gitee\cook-frame)
${sys:applicationName} 2023-09-18 10:18:34  INFO ServerCaseApplication:648 - No active profile set, falling back to default profiles: default
${sys:applicationName} 2023-09-18 10:18:34  INFO TomcatWebServer:108 - Tomcat initialized with port(s): 7081 (http)
${sys:applicationName} 2023-09-18 10:18:34  INFO Http11NioProtocol:173 - Initializing ProtocolHandler ["http-nio-7081"]
${sys:applicationName} 2023-09-18 10:18:34  INFO StandardService:173 - Starting service [Tomcat]
${sys:applicationName} 2023-09-18 10:18:34  INFO StandardEngine:173 - Starting Servlet engine: [Apache Tomcat/9.0.46]
${sys:applicationName} 2023-09-18 10:18:34  INFO [/]:173 - Initializing Spring embedded WebApplicationContext
${sys:applicationName} 2023-09-18 10:18:34  INFO ServletWebServerApplicationContext:285 - Root WebApplicationContext: initialization completed in 795 ms
 _ _   |_  _ _|_. ___ _ |    _ 
| | |\/|_)(_| | |_\  |_)||_|_\ 
     /               |         
                        3.5.1 
service-case 2023-09-18 10:18:35  INFO ThreadPoolTaskExecutor:181 - Initializing ExecutorService 'applicationTaskExecutor'
service-case 2023-09-18 10:18:35  INFO PropertySourcedRequestMappingHandlerMapping:69 - Mapped URL path [/v2/api-docs] onto method [springfox.documentation.swagger2.web.Swagger2Controller#getDocumentation(String, HttpServletRequest)]
service-case 2023-09-18 10:18:35  INFO Http11NioProtocol:173 - Starting ProtocolHandler ["http-nio-7081"]
service-case 2023-09-18 10:18:35  INFO TomcatWebServer:220 - Tomcat started on port(s): 7081 (http) with context path ''

可以看到比较靠前的日志输出中的applicationName变量是没有被替换成真正的服务名的。

那怎么办呢？

分析

所以我们要从SpringBoot的启动过程入手

SpringApplication#run(String… args)

public ConfigurableApplicationContext run(String... args) {
    StopWatch stopWatch = new StopWatch();
    stopWatch.start();
    ConfigurableApplicationContext context = null;
    configureHeadlessProperty();
    SpringApplicationRunListeners listeners = getRunListeners(args);
    listeners.starting();
    try {
        ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
        ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
        configureIgnoreBeanInfo(environment);
        Banner printedBanner = printBanner(environment);
        context = createApplicationContext();
        prepareContext(context, environment, listeners, applicationArguments, printedBanner);
        refreshContext(context);
        afterRefresh(context, applicationArguments);
        stopWatch.stop();
        if (this.logStartupInfo) {
            new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
        }
        listeners.started(context);
        callRunners(context, applicationArguments);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, listeners);
        throw new IllegalStateException(ex);
    }

    try {
        listeners.running(context);
    }
    catch (Throwable ex) {
        handleRunFailure(context, ex, null);
        throw new IllegalStateException(ex);
    }
    return context;
}

突破点在environment的创建这步骤，所以分析prepareEnvironment(listeners, applicationArguments)看能不能实现我们想要的需求

SpringApplication#prepareEnvironment

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
        ApplicationArguments applicationArguments) {
    // Create and configure the environment
    ConfigurableEnvironment environment = getOrCreateEnvironment();
    configureEnvironment(environment, applicationArguments.getSourceArgs());
    ConfigurationPropertySources.attach(environment);
    //经过debug发现当这步方法执行完后，environment.getProperty("spring.application.name")是可以获取值
    listeners.environmentPrepared(environment);
    bindToSpringApplication(environment);
    if (!this.isCustomEnvironment) {
        environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
                deduceEnvironmentClass());
    }
    ConfigurationPropertySources.attach(environment);
    return environment;
}

listeners.environmentPrepared(environment);为关键点，environment.getProperty("spring.application.name")就是在此进行完成的，所以我们要进入分析。

SpringApplicationRunListeners#environmentPrepared

void environmentPrepared(ConfigurableEnvironment environment) {
    for (SpringApplicationRunListener listener : this.listeners) {
        listener.environmentPrepared(environment);
    }
}

listeners有一个实现类EventPublishingRunListener

public void environmentPrepared(ConfigurableEnvironment environment) {
    this.initialMulticaster
            .multicastEvent(new ApplicationEnvironmentPreparedEvent(this.application, this.args, environment));
}

这里是发布了一个ApplicationEnvironmentPreparedEvent事件。

既然有发布，就有监听。我们接下来分析下监听事件的逻辑

ConfigFileApplicationListener#onApplicationEvent

public void onApplicationEvent(ApplicationEvent event) {
    if (event instanceof ApplicationEnvironmentPreparedEvent) {
        onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);
    }
    if (event instanceof ApplicationPreparedEvent) {
        onApplicationPreparedEvent(event);
    }
}

private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {
    List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
    postProcessors.add(this);
    AnnotationAwareOrderComparator.sort(postProcessors);
    for (EnvironmentPostProcessor postProcessor : postProcessors) {
        postProcessor.postProcessEnvironment(event.getEnvironment(), event.getSpringApplication());
    }
}

postProcessors有多个，其中ConfigFileApplicationListener就是设置spring.applicaton.name的值。至于怎么设置的，就不进去分析了，有兴趣的同学可以自行去仔细研究。

通常上述分析，我们知道了Environment设置spring.applicaton.name值的步骤，那么我们可不可以紧接着，这个设置步骤之后就进行自定义设值，然后让log4j2来取呢？

答案是当然可以！

让我们回到SpringApplicationRunListeners#environmentPrepared

SpringApplicationRunListeners#environmentPrepared

void environmentPrepared(ConfigurableEnvironment environment) {
    for (SpringApplicationRunListener listener : this.listeners) {
        listener.environmentPrepared(environment);
    }
}

默认listeners为一个，那我们只要自己实现一个，让listeners为2个，第一个默认执行完后，不就能紧接着执行我们的了吗，那我们分析下listeners是怎么来的

SpringApplication#getRunListeners

private SpringApplicationRunListeners getRunListeners(String[] args) {
    Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
    return new SpringApplicationRunListeners(logger,
            getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args));
}

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
    ClassLoader classLoader = getClassLoader();
    // Use names and ensure unique to protect against duplicates
    Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
    List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
    AnnotationAwareOrderComparator.sort(instances);
    return instances;
}

SpringFactoriesLoader.loadFactoryNames(type, classLoader)和自动装配的方法很像啊，那去看一眼

org.springframework.boot.SpringApplicationRunListener=\
org.springframework.boot.context.event.EventPublishingRunListener

果然在文件中指定了org.springframework.boot.context.event.EventPublishingRunListener，也就是默认的SpringApplicationRunListener实现类。

然后在分析createSpringFactoriesInstances看看是如何加载的

private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes,
        ClassLoader classLoader, Object[] args, Set<String> names) {
    List<T> instances = new ArrayList<>(names.size());
    for (String name : names) {
        try {
            Class<?> instanceClass = ClassUtils.forName(name, classLoader);
            Assert.isAssignable(type, instanceClass);
            Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
            T instance = (T) BeanUtils.instantiateClass(constructor, args);
            instances.add(instance);
        }
        catch (Throwable ex) {
            throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, ex);
        }
    }
    return instances;
}

这里就是创建对象的过程了，用的是有参构造方法需要两个参数constructor, args，所以我们参考EventPublishingRunListener的结构来实现即可

实现

自定义SpringApplicationRunListener的实现类CustomEventPublishingRunListener

CustomEventPublishingRunListener

public class CustomEventPublishingRunListener implements SpringApplicationRunListener, Ordered {
    
    private static final String SPRING_APPLICATION_NAME = "spring.application.name";
    
    private final SpringApplication application;
    
    private final String[] args;
    
    public CustomEventPublishingRunListener(SpringApplication application, String[] args){
        this.application = application;
        this.args = args;
    }
    @Override
    public int getOrder() {
        return 1;
    }
    
    @Override
    public void environmentPrepared(ConfigurableEnvironment environment) {
        String applicationName = environment.getProperty(SPRING_APPLICATION_NAME);
        if (StringUtil.isNotEmpty(applicationName)) {
            System.setProperty("applicationName", applicationName);
        }
    }
}

• 有参构造方法中的SpringApplication application, String[] args参数为固定的
• getOrder返回的值要为1，因为EventPublishingRunListener中的getOrder返回值为0

在自动装配文件spring.factories指定位置

org.springframework.boot.SpringApplicationRunListener=\
  com.example.runlistener.CustomEventPublishingRunListener

在log4j2的xml文件中进行取值

<Console name="Console" target="SYSTEM_OUT">
    
    <PatternLayout pattern="${sys:applicationName} %d{yyyy-MM-dd HH:mm:ss} %5p %c{1}:%L - %m%n"/>
Console>

输出结果

service-case 2023-09-18 14:57:25  INFO ServerCaseApplication:55 - Starting ServerCaseApplication on lukuan with PID 20004 (D:\idea_work_my\gitee\cook-frame\server\server-case\target\classes started by lukuan in D:\idea_work_my\gitee\cook-frame)
service-case 2023-09-18 14:57:25  INFO ServerCaseApplication:648 - No active profile set, falling back to default profiles: default
service-case 2023-09-18 14:57:25  INFO TomcatWebServer:108 - Tomcat initialized with port(s): 7081 (http)
service-case 2023-09-18 14:57:25  INFO Http11NioProtocol:173 - Initializing ProtocolHandler ["http-nio-7081"]
service-case 2023-09-18 14:57:25  INFO StandardService:173 - Starting service [Tomcat]
service-case 2023-09-18 14:57:25  INFO StandardEngine:173 - Starting Servlet engine: [Apache Tomcat/9.0.46]
service-case 2023-09-18 14:57:25  INFO [/]:173 - Initializing Spring embedded WebApplicationContext
service-case 2023-09-18 14:57:25  INFO ServletWebServerApplicationContext:285 - Root WebApplicationContext: initialization completed in 716 ms
 _ _   |_  _ _|_. ___ _ |    _ 
| | |\/|_)(_| | |_\  |_)||_|_\ 
     /               |         
                        3.5.1 
service-case 2023-09-18 14:57:26  INFO ThreadPoolTaskExecutor:181 - Initializing ExecutorService 'applicationTaskExecutor'
service-case 2023-09-18 14:57:26  INFO PropertySourcedRequestMappingHandlerMapping:69 - Mapped URL path [/v2/api-docs] onto method [springfox.documentation.swagger2.web.Swagger2Controller#getDocumentation(String, HttpServletRequest)]
service-case 2023-09-18 14:57:26  INFO Http11NioProtocol:173 - Starting ProtocolHandler ["http-nio-7081"]
service-case 2023-09-18 14:57:26  INFO TomcatWebServer:220 - Tomcat started on port(s): 7081 (http) with context path ''
....

可以看到实现了我们想要的功能