最近在写一个logback的kafka appender,无意中发现spring-boot在使用logback时的一个坑
用ConsoleAppender.java来举例,假设在logback.xml中使用了该appender,那么这个类的相关的初始化方法都会调两次,如start()方法
打断点进行debug,第一次进入start()方法如下:
可以看到所有的调用链(除了自己代码的方法)都是logback或者slf4j相关的比较正常
当跳过该断点时又会进入以此这个方法,看下调用链:
可以看到这次的初始化是由spring-boot发起的,所以这样logback初始化一次,然后spring-boot初始化一次,一共两次
我们现在可以将spring-boot的初始化去掉
debug代码可以发现LoggingApplicationListener.java这个监听器主要是用来初始化spring-boot的日志系统,现在目的将该listener在启动之前去掉
spring-boot的启动代码为:
new SpringApplicationBuilder(Launcher.class).application().run(args);
在SpringApplicationBuilder.java的构造方法打断点进行跟踪,
进入SpringAppication.java会发现该类中的代码:
private void initialize(Object[] sources) { if (sources != null && sources.length > 0) { this.sources.addAll(Arrays.asList(sources)); } this.webEnvironment = deduceWebEnvironment(); setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class)); setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); this.mainApplicationClass = deduceMainApplicationClass(); }
第八行应该就是注册监听器的地方了,继续往下跟踪,进入以下方法:
privateCollection extends T> getSpringFactoriesInstances(Class type, Class>[] parameterTypes, Object... args) { ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); // Use names and ensure unique to protect against duplicates Set names = new LinkedHashSet ( SpringFactoriesLoader.loadFactoryNames(type, classLoader)); List instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names); AnnotationAwareOrderComparator.sort(instances); return instances; }
继续进入loadFactoryNames()方法,核心就在这里了
public static ListloadFactoryNames(Class> factoryClass, ClassLoader classLoader) { String factoryClassName = factoryClass.getName(); try { Enumeration urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) : ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION)); List result = new ArrayList (); while (urls.hasMoreElements()) { URL url = urls.nextElement(); Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url)); String factoryClassNames = properties.getProperty(factoryClassName); result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames))); } return result; } catch (IOException ex) { throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() + "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex); } }
FACTORIES_RESOURCE_LOCATION这个常量的值为META-INF/spring.factories,
打开该文件可以发现:
# PropertySource Loaders org.springframework.boot.env.PropertySourceLoader=\ org.springframework.boot.env.PropertiesPropertySourceLoader,\ org.springframework.boot.env.YamlPropertySourceLoader # Run Listeners org.springframework.boot.SpringApplicationRunListener=\ org.springframework.boot.context.event.EventPublishingRunListener # Application Context Initializers org.springframework.context.ApplicationContextInitializer=\ org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\ org.springframework.boot.context.ContextIdApplicationContextInitializer,\ org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\ org.springframework.boot.context.web.ServerPortInfoApplicationContextInitializer # Application Listeners org.springframework.context.ApplicationListener=\ org.springframework.boot.ClearCachesApplicationListener,\ org.springframework.boot.builder.ParentContextCloserApplicationListener,\ org.springframework.boot.context.FileEncodingApplicationListener,\ org.springframework.boot.context.config.AnsiOutputApplicationListener,\ org.springframework.boot.context.config.ConfigFileApplicationListener,\ org.springframework.boot.context.config.DelegatingApplicationListener,\ org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener,\ org.springframework.boot.logging.ClasspathLoggingApplicationListener,\ org.springframework.boot.logging.LoggingApplicationListener # Environment Post Processors org.springframework.boot.env.EnvironmentPostProcessor=\ org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\ org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor # Failure Analyzers org.springframework.boot.diagnostics.FailureAnalyzer=\ org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.BindFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.NoUniqueBeanDefinitionFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.PortInUseFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.ValidationExceptionFailureAnalyzer # FailureAnalysisReporters org.springframework.boot.diagnostics.FailureAnalysisReporter=\ org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter
ApplicationListener应该就是我们需要修改的地方了,去掉org.springframework.boot.logging.LoggingApplicationListener就可以了,我们可以在代码里面覆盖一份这块代码从而实现去掉这行,但是实际得再跑一遍,发现还是一样初始化两次
问题出在
Enumerationurls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) : ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
这块代码是将所有的META-INF/spring.factories都读取过来了然后进行合并,所以说哦这个META-INF/spring.factories只能增加内容,但是不能去掉某些内容,没办法了只能在代码初始化了所有的listener之后再将listener去掉,
具体代码如下(启动spring-boot的main方法中):
SpringApplicationBuilder builder = new SpringApplicationBuilder(Launcher.class); Set> listeners = builder.application().getListeners(); for (Iterator > it = listeners.iterator(); it.hasNext();) { ApplicationListener> listener = it.next(); if (listener instanceof LoggingApplicationListener) { it.remove(); } } builder.application().setListeners(listeners); builder.run(args);
PS:其实log初始化两次并无伤大雅,关键是遇到了问题总是想解决下或者了解下原理
以上为个人经验,希望能给大家一个参考,也希望大家多多支持脚本之家。