如果您看过之前的Spring Boot 1.x教程，或者自己原本就对Spring Boot有一些经验，或者对Spring MVC很熟悉。那么对于Spring构建的Web应用在启动的时候，都会输出当前应用创建的HTTP接口列表。
比如下面的这段日志：
2020-02-11 15:32:39.293 INFO 48395 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler] 2020-02-11 15:32:39.482 INFO 48395 --- [ main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@7ff95560: startup date [Tue Feb 11 15:32:37 CST 2020]; root of context hierarchy 2020-02-11 15:32:39.568 INFO 48395 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/users/{id}],methods=[GET]}" onto public com.didispace.chapter26.User com.didispace.chapter26.UserController.getUser(java.lang.Long) 2020-02-11 15:32:39.569 INFO 48395 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/users/{id}],methods=[PUT]}" onto public java.lang.String com.didispace.chapter26.UserController.putUser(java.lang.Long,com.didispace.chapter26.User) 2020-02-11 15:32:39.570 INFO 48395 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/users/],methods=[GET]}" onto public java.util.List<com.didispace.chapter26.User> com.didispace.chapter26.UserController.getUserList() 2020-02-11 15:32:39.570 INFO 48395 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/users/],methods=[POST]}" onto public java.lang.String com.didispace.chapter26.UserController.postUser(com.didispace.chapter26.User) 2020-02-11 15:32:39.570 INFO 48395 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/users/{id}],methods=[DELETE]}" onto public java.lang.String com.didispace.chapter26.UserController.deleteUser(java.lang.Long) 2020-02-11 15:32:39.573 INFO 48395 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest) 2020-02-11 15:32:39.573 INFO 48395 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse) 2020-02-11 15:32:39.590 INFO 48395 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler] 2020-02-11 15:32:39.590 INFO 48395 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
这些日志接口信息是由org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping类在启动的时候，通过扫描Spring MVC的@Controller、@RequestMapping等注解去发现应用提供的所有接口信息。然后在日志中打印，以方便开发者排查关于接口相关的启动是否正确。
但是，足够仔细的开发者可能已经发现，从Spring Boot 2.1.0版本开始，就不再打印这些信息了，完整的启动日志变的非常少，以Spring Boot 2.x基础教程：构建RESTful API与单元测试一文的例子为例，可以看到输入内容如下：
2020-02-11 15:34:15.280 INFO 48784 --- [main] c.d.chapter26.Chapter26Application : Starting Chapter26Application on zhaiyongchaodeMacBook-Pro.local with PID 48784 (/Users/zhaiyongchao/Documents/git/github/SpringBoot-Learning/2.1.x/chapter2-6/target/classes started by zhaiyongchao in /Users/zhaiyongchao/Documents/git/github/SpringBoot-Learning/2.1.x) 2020-02-11 15:34:15.283 INFO 48784 --- [main] c.d.chapter26.Chapter26Application : No active profile set, falling back to default profiles: default 2020-02-11 15:34:16.556 INFO 48784 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http) 2020-02-11 15:34:16.587 INFO 48784 --- [main] o.apache.catalina.core.StandardService : Starting service [Tomcat] 2020-02-11 15:34:16.588 INFO 48784 --- [main] org.apache.catalina.core.StandardEngine : Starting Servlet engine: [Apache Tomcat/9.0.16] 2020-02-11 15:34:16.596 INFO 48784 --- [main] o.a.catalina.core.AprLifecycleListener : The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: [/Users/zhaiyongchao/Library/Java/Extensions:/Library/Java/Extensions:/Network/Library/Java/Extensions:/System/Library/Java/Extensions:/usr/lib/java:.] 2020-02-11 15:34:16.702 INFO 48784 --- [main] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext 2020-02-11 15:34:16.702 INFO 48784 --- [main] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 1377 ms 2020-02-11 15:34:16.954 INFO 48784 --- [main] o.s.s.concurrent.ThreadPoolTaskExecutor : Initializing ExecutorService 'applicationTaskExecutor' 2020-02-11 15:34:17.187 INFO 48784 --- [main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path '' 2020-02-11 15:34:17.192 INFO 48784 --- [main] c.d.chapter26.Chapter26Application : Started Chapter26Application in 2.238 seconds (JVM running for 2.764)
找回日志中请求路径列表
为什么在Spring Boot 2.1.x版本中不再打印请求路径列表呢？
主要是由于从该版本开始，将这些日志的打印级别做了调整：从原来的INFO调整为TRACE。所以，当我们希望在应用启动的时候打印这些信息的话，只需要在配置文件增增加对RequestMappingHandlerMapping类的打印级别设置即可，比如在application.properties中增加下面这行配置：
logging.level.org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping=trace
在增加了上面的配置之后重启应用，便可以看到如下的日志打印：
2020-02-11 15:36:09.787 TRACE 49215 --- [main] s.w.s.m.m.a.RequestMappingHandlerMapping : c.d.c.UserController: {PUT /users/{id}}: putUser(Long,User) {GET /users/{id}}: getUser(Long) {POST /users/}: postUser(User) {GET /users/}: getUserList() {DELETE /users/{id}}: deleteUser(Long) 2020-02-11 15:36:09.791 TRACE 49215 --- [main] s.w.s.m.m.a.RequestMappingHandlerMapping : o.s.b.a.w.s.e.BasicErrorController: { /error}: error(HttpServletRequest) { /error, produces [text/html]}: errorHtml(HttpServletRequest,HttpServletResponse) 2020-02-11 15:36:09.793 DEBUG 49215 --- [main] s.w.s.m.m.a.RequestMappingHandlerMapping : 7 mappings in 'requestMappingHandlerMapping'
可以看到在2.1.x版本之后，除了调整了日志级别之外，对于打印内容也做了调整。现在的打印内容根据接口创建的Controller类做了分类打印，这样更有助于开发者根据自己编写的Controller来查找初始化了那些HTTP接口。
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代码示例
本文的完整工程可以查看下面仓库中的chapter2-6目录：
