Spring Boot 探索系列 - 自动化配置篇

26. Logging

Spring Boot uses Commons Logging for all internal logging, but leaves the underlying log implementation open. Default configurations are provided for Java Util Logging,Log4J, Log4J2 and Logback. In each case loggers are pre-configured to use console output with optional file output also available.

By default, If you use the ‘Starter POMs’, Logback will be used for logging. Appropriate Logback routing is also included to ensure that dependent libraries that use Java Util Logging, Commons Logging, Log4J or SLF4J will all work correctly.

	There are a lot of logging frameworks available for Java. Don’t worry if the above list seems confusing. Generally you won’t need to change your logging dependencies and the Spring Boot defaults will work just fine.

26.1 Log format

The default log output from Spring Boot looks like this:

2014-03-05 10:57:51.112  INFO 45469 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/7.0.52
2014-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2014-03-05 10:57:51.253  INFO 45469 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1358 ms
2014-03-05 10:57:51.698  INFO 45469 --- [ost-startStop-1] o.s.b.c.e.ServletRegistrationBean        : Mapping servlet: ‘dispatcherServlet‘ to [/]
2014-03-05 10:57:51.702  INFO 45469 --- [ost-startStop-1] o.s.b.c.embedded.FilterRegistrationBean  : Mapping filter: ‘hiddenHttpMethodFilter‘ to: [/*]

The following items are output:

• Date and Time — Millisecond precision and easily sortable.
• Log Level — ERROR, WARN, INFO, DEBUG or TRACE.
• Process ID.
• A --- separator to distinguish the start of actual log messages.
• Thread name — Enclosed in square brackets (may be truncated for console output).
• Logger name — This is usually the source class name (often abbreviated).
• The log message.

	Logback does not have a FATAL level (it is mapped to ERROR)

26.2 Console output

The default log configuration will echo messages to the console as they are written. By default ERROR, WARN and INFO level messages are logged. You can also enable a “debug” mode by starting your application with a --debug flag.

$ java -jar myapp.jar --debug

	you can also specify debug=true in your application.properties.

When the debug mode is enabled, a selection of core loggers (embedded container, Hibernate and Spring) are configured to output more information. Enabling the debug mode does not configure your application log all messages with DEBUG level.

26.2.1 Color-coded output

If your terminal supports ANSI, color output will be used to aid readability. You can set spring.output.ansi.enabled to a supported value to override the auto detection.

Color coding is configured using the %clr conversion word. In its simplest form the converter will color the output according to the log level, for example:

%clr(%5p)

The mapping of log level to a color is as follows:

Alternatively, you can specify the color or style that should be used by providing it as an option to the conversion. For example, to make the text yellow:

%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){yellow}

The following colors and styles are supported:

• blue
• cyan
• faint
• green
• magenta
• red
• yellow

26.3 File output

By default, Spring Boot will only log to the console and will not write log files. If you want to write log files in addition to the console output you need to set a logging.file orlogging.path property (for example in your application.properties).

The following table shows how the logging.* properties can be used together:

Table 26.1. Logging properties

Log files will rotate when they reach 10 Mb and as with console output, ERROR, WARN and INFO level messages are logged by default.

	The logging system is initialized early in the application lifecycle and as such logging properties will not be found in property files loaded via @PropertySourceannotations.

	Logging properties are independent of the actual logging infrastructure. As a result, specific configuration keys (such as logback.configurationFile for Logback) are not managed by spring Boot.

26.4 Log Levels

All the supported logging systems can have the logger levels set in the Spring Environment (so for example in application.properties) using ‘logging.level.*=LEVEL’ where ‘LEVEL’ is one of TRACE, DEBUG, INFO, WARN, ERROR, FATAL, OFF. The root logger can be configured using logging.level.root. Exampleapplication.properties:

logging.level.root=WARN
logging.level.org.springframework.web=DEBUG
logging.level.org.hibernate=ERROR

	By default Spring Boot remaps Thymeleaf INFO messages so that they are logged at DEBUG level. This helps to reduce noise in the standard log output. SeeLevelRemappingAppender for details of how you can apply remapping in your own configuration.

26.5 Custom log configuration

The various logging systems can be activated by including the appropriate libraries on the classpath, and further customized by providing a suitable configuration file in the root of the classpath, or in a location specified by the Spring Environment property logging.config.

	Since logging is initialized before the ApplicationContext is created, it isn’t possible to control logging from @PropertySources in Spring@Configuration files. System properties and the conventional Spring Boot external configuration files work just fine.)

Depending on your logging system, the following files will be loaded:

	When possible we recommend that you use the -spring variants for your logging configuration (for example logback-spring.xml rather thanlogback.xml). If you use standard configuration locations, Spring cannot completely control log initialization.

	There are known classloading issues with Java Util Logging that cause problems when running from an ‘executable jar’. We recommend that you avoid it if at all possible.

To help with the customization some other properties are transferred from the Spring Environment to System properties:

All the logging systems supported can consult System properties when parsing their configuration files. See the default configurations in spring-boot.jar for examples.

	If you want to use a placeholder in a logging property, you should use Spring Boot’s syntax and not the syntax of the underlying framework. Notably, if you’re using Logback, you should use : as the delimiter between a property name and its default value and not :-.

You can add MDC and other ad-hoc content to log lines by overriding only the LOG_LEVEL_PATTERN (or logging.pattern.level with Logback). For example, if you use logging.pattern.level=user:%X{user} %5p then the default log format will contain an MDC entry for "user" if it exists, e.g. 2015-09-30 12:30:04.031 user:juergen INFO 22174 --- [ nio-8080-exec-0] demo.Controller Handling authenticated request

26.6 Logback extensions

Spring Boot includes a number of extensions to Logback which can help with advanced configuration. You can use these extensions in your logback-spring.xmlconfiguration file.

	You cannot use extensions in the standard logback.xml configuration file since it’s loaded too early. You need to either use logback-spring.xml or define a logging.config property.

26.6.1 Profile-specific configuration

The <springProfile> tag allows you to optionally include or exclude sections of configuration based on the active Spring profiles. Profile sections are supported anywhere within the <configuration> element. Use the name attribute to specify which profile accepts the configuration. Multiple profiles can be specified using a comma-separated list.

<springProfile name="staging">
    <!-- configuration to be enabled when the "staging" profile is active -->
</springProfile>

<springProfile name="dev, staging">
    <!-- configuration to be enabled when the "dev" or "staging" profiles are active -->
</springProfile>

<springProfile name="!production">
    <!-- configuration to be enabled when the "production" profile is not active -->
</springProfile>

26.6.2 Environment properties

The <springProperty> tag allows you to surface properties from the Spring Environment for use within Logback. This can be useful if you want to access values from your application.properties file in your logback configuration. The tag works in a similar way to Logback’s standard <property> tag, but rather than specifying a direct value you specify the source of the property (from the Environment). You can use the scope attribute if you need to store the property somewhere other than inlocal scope.

<springProperty scope="context" name="fluentHost" source="myapp.fluentd.host"/>
<appender name="FLUENT" class="ch.qos.logback.more.appenders.DataFluentAppender">
    <remoteHost>${fluentHost}</remoteHost>
    ...
</appender>

	The RelaxedPropertyResolver is used to access Environment properties. If specify the source in dashed notation (my-property-name) all the relaxed variations will be tried (myPropertyName, MY_PROPERTY_NAME etc).

http://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-logging.html

作者：孙立伟
链接：https://zhuanlan.zhihu.com/p/19958535
来源：知乎
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。

基于Spring Boot的应用，程序的入口是SpringApplication类。通过@EnableAutoConfiguration 开启Spring Boot的自动配置功能。这个是Spring Boot核心价值之一。我们首先要搞清楚的应该是Spring Boot如何自动的配置所有的特性以及如何定制自动化配置过程。这里列出几个在官方参考文档中和自动化配置相关的链接。

23. Externalized Configuration

36. Developing auto-configuration and using conditions

62.1. Troubleshoot auto-configuration

63. Properties & configuration

Appendix A. Common application properties

Appendix C. Auto-configuration classes

如何阅读自动化配置相关源代码

通过阅读以上参考资料，大致可以搞清楚Spring Boot自动化配置的过程需要遵循的方向。但是，阅读源代码是了解Spring Boot的自动配置机制的最佳选择。源代码链接：spring-projects/spring-boot · GitHub。整个项目使用Maven进行管理，直接导入即可。注意不要导入太多的Maven项目，我们的目的是通过阅读代码来加深Spring Boot的理解，只需要‘spring-boot‘, ‘spring-boot-actuator‘ 和 ‘spring-boot-autoconfigure‘。

Spring Boot 自动化配置相关源代码阅读起来并不困难，在官方文档中也有一些提示。在读完官方文档的基础上，才能开始阅读源码。我把目前了解到的关键类列一下。

另外，补充说明一点，本系列文章均基于 Spring Boot 1.2.1.RELEASE 版本。

1. SpringApplication (Spring Boot Docs 1.2.1.RELEASE API)
2. ConfigFileApplicationListener (Spring Boot Docs 1.2.1.RELEASE API)

Spring Boot通过实现各种ApplicationListener进行实际的配置工作，配置框架是使用Environment 和 PropertySource相关的类。几点注意事项：

• Spring Boot支持从多个地方加载配置，比如命令行、系统环境变量、JNDI等，因此配置项的语法支持所谓的RelaxedEnvironment。在源码中，通过查找 Relaxed开头的类，比如RelaxedPropertyResolver，可以了解到相关的使用情况
• SpringBoot同时支持YAML和Properties格式的配置文件，虽然并不禁止混合使用，但是加载顺序是不确定的。

日志框架配置文件位置‘logging.config‘的一个坑

在Spring Boot 1.2.1中，对于日志框架本身的配置文件位置是通过‘logging.config‘进行设置的。下面是LoggingApplicationListener的代码片段：

private void initializeSystem(ConfigurableEnvironment environment,
      LoggingSystem system) {
   LogFile logFile = LogFile.get(environment);
   String logConfig = environment.getProperty(CONFIG_PROPERTY);
   if (StringUtils.hasLength(logConfig)) {
try {
         //码农公社：校验logConfig是否可访问
         ResourceUtils.getURL(logConfig).openStream().close();
         system.initialize(logConfig, logFile);
      }
catch (Exception ex) {
this.logger.warn("Logging environment value ‘" + logConfig
               + "‘ cannot be opened and will be ignored "
               + "(using default location instead)");
         system.initialize(null, logFile);
      }
   }
else {
      system.initialize(null, logFile);
   }
}

(知乎专栏不支持对代码加行号，很不方便啊！）

关键是这一行代码：

ResourceUtils.getURL(logConfig).openStream().close();

得到‘logging.config‘（即常量 CONFIG_PROPERTY)所配置的值后，LoggingApplicationListener先调用ResourceUtils.geURL().openStream() 校验指定的位置是否可读。下面是 ResourceUtils.getURL的源码：

public static URL getURL(String resourceLocation) throws FileNotFoundException {
   Assert.notNull(resourceLocation, "Resource location must not be null");
   if (resourceLocation.startsWith(CLASSPATH_URL_PREFIX)) {
      String path = resourceLocation.substring(CLASSPATH_URL_PREFIX.length());
      ClassLoader cl = ClassUtils.getDefaultClassLoader();
      URL url = (cl != null ? cl.getResource(path) : ClassLoader.getSystemResource(path));
      if (url == null) {
         String description = "class path resource [" + path + "]";
         throw new FileNotFoundException(description +
" cannot be resolved to URL because it does not exist");
      }
return url;
   }
try {
// try URL
      // 码农笔记：logging.config必须使用真实的文件路径，不能是合法的URL语法
      return new URL(resourceLocation);
   }
catch (MalformedURLException ex) {
// no URL -> treat as file path
      try {
return new File(resourceLocation).toURI().toURL();
      }
catch (MalformedURLException ex2) {
throw new FileNotFoundException("Resource location [" + resourceLocation +
"] is neither a URL not a well-formed file path");
      }
   }
}

从上面的代码可得知，‘logging.config‘如果指定的是文件系统位置，必须直接写文件路径，不能加"file:/"前缀。 从而让 "new URL"抛出MalformedURLException，ResourceUtils.getURL才能返回一个正确的文件URL。

‘logging.config‘的写法文档中没有明确的说明，因此我一开始误以为都必须加前缀如classpath: 或者 file:。

https://zhuanlan.zhihu.com/p/19958535