devtools模組，是為開發者服務的一個模組。主要的功能就是程式碼修改後一般在5秒之內就會自動重新載入至伺服器，相當於restart成功。

spring-boot提供的重新啟動技術使用兩個類載入器，一個類載入器用來載入那些不變的類（如第三方jar包提供的類），另外一個用來載入正在開發的程式碼類，你正在開發的類被載入進了一個重新啟動類載入器中，當應用程式 重新啟動時會拋棄掉之前的類載入器，然後重新建立一個重新啟動的類載入器，所以使用DevTools工具模組重新部署程式碼是很快的。

只要我們修改了classpath下任何檔案只要儲存Devtools模組都會重新啟動應用程式。

一、spring-boot-devtools模組是一個為開發者服務的模組，其中最重要的功能就是程式碼的熱部署，只需在pom檔案中加入如下依賴不需要任何其他的配置

<dependencies>
	<dependency>
		<groupId>org.springframework.boot</groupId>
		<artifactId>spring-boot-devtools</artifactId>
		<optional>true</optional>
	</dependency>
</dependencies>

2017-10-15 17:14:58.619  INFO 1519 --- [       Thread-6] ConfigServletWebServerApplicationContext : Closing org.springframework.boot.web.ser
 
[email protected]895709: startup date [Sun Oct 15 17:14:20 CST 2017]; root of context hierarchy
2017-10-15 17:14:58.624  WARN 1519 --- [       Thread-6] o.s.b.f.support.DisposableBeanAdapter    : Invocation of destroy method failed on bean with name 'classPathFileSystemWatcher': java.lang.NullPointerException
2017-10-15 17:14:58.625  INFO 1519 --- [       Thread-6] o.s.j.e.a.AnnotationMBeanExporter        : Unregistering JMX-exposed beans on shutdown

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::  (v2.0.0.BUILD-SNAPSHOT)

2017-10-15 17:14:58.876  INFO 1519 --- [  restartedMain] ggauthority.v1.GgauthorityApplication    : Starting GgauthorityApplication on yaomingyangdeMacBook-Pro.local with PID 1519 (/Users/yaomingyang/Documents/IDE/workplace/ggauthority/target/classes started by yaomingyang in /Users/yaomingyang/Documents/IDE/workplace/ggauthority)
2017-10-15 17:14:58.877  INFO 1519 --- [  restartedMain] ggauthority.v1.GgauthorityApplication    : No active profile set, falling back to default profiles: default
2017-10-15 17:14:58.880  INFO 1519 --- [  restartedMain] ConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.ser
 
[email protected]2fc9f5: startup date [Sun Oct 15 17:14:58 CST 2017]; root of context hierarchy
2017-10-15 17:14:59.401  INFO 1519 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8011 (http)
2017-10-15 17:14:59.402  INFO 1519 --- [  restartedMain] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2017-10-15 17:14:59.403  INFO 1519 --- [  restartedMain] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.23
2017-10-15 17:14:59.409  INFO 1519 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2017-10-15 17:14:59.410  INFO 1519 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 530 ms
2017-10-15 17:14:59.446  INFO 1519 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Mapping servlet: 'dispatcherServlet' to [/]
2017-10-15 17:14:59.447  INFO 1519 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2017-10-15 17:14:59.447  INFO 1519 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2017-10-15 17:14:59.447  INFO 1519 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2017-10-15 17:14:59.447  INFO 1519 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2017-10-15 17:14:59.480  INFO 1519 --- [  restartedMain] org.mongodb.driver.cluster               : Cluster created with settings {hosts=[127.0.0.1:27017], mode=SINGLE, requiredClusterType=UNKNOWN, serverSelectionTimeout='30000 ms', maxWaitQueueSize=500}
2017-10-15 17:14:59.547  INFO 1519 --- [127.0.0.1:27017] org.mongodb.driver.connection            : Opened connection [connectionId{localValue:2, serverValue:19}] to 127.0.0.1:27017
2017-10-15 17:14:59.548  INFO 1519 --- [127.0.0.1:27017] org.mongodb.driver.cluster               : Monitor thread successfully connected to server with description ServerDescription{address=127.0.0.1:27017, type=STANDALONE, state=CONNECTED, ok=true, version=ServerVersion{versionList=[3, 2, 11]}, minWireVersion=0, maxWireVersion=4, maxDocumentSize=16777216, roundTripTimeNanos=635614}
2017-10-15 17:14:59.678  INFO 1519 --- [  restartedMain] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.web.ser[email protected]2fc9f5: startup date [Sun Oct 15 17:14:58 CST 2017]; root of context hierarchy
2017-10-15 17:14:59.691  INFO 1519 --- [  restartedMain] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/users/list],methods=[GET || POST]}" onto public ggauthority.v1.user.entity.User ggauthority.v1.user.controller.UserController.list(java.lang.Long)
2017-10-15 17:14:59.691  INFO 1519 --- [  restartedMain] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/users/get_user/{user_id}],methods=[GET || POST]}" onto public java.util.Map<java.lang.String, java.lang.Object> ggauthority.v1.user.controller.UserController.get_user(java.lang.Long)
2017-10-15 17:14:59.696  INFO 1519 --- [  restartedMain] 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)
2017-10-15 17:14:59.696  INFO 1519 --- [  restartedMain] 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)
2017-10-15 17:14:59.708  INFO 1519 --- [  restartedMain] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-10-15 17:14:59.709  INFO 1519 --- [  restartedMain] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-10-15 17:14:59.727  INFO 1519 --- [  restartedMain] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-10-15 17:14:59.776  INFO 1519 --- [  restartedMain] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
2017-10-15 17:14:59.883  INFO 1519 --- [  restartedMain] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2017-10-15 17:14:59.904  INFO 1519 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8011 (http)
2017-10-15 17:14:59.907  INFO 1519 --- [  restartedMain] ggauthority.v1.GgauthorityApplication    : Started GgauthorityApplication in 1.07 seconds (JVM running for 40.767)

三、當你更改不在classpath下的檔案你可能想讓你的應用程式重新啟動或者只加載對應的檔案，你可以使用spring.devtools.restart.additional-paths屬性配置檔案將對應的檔案載入到devtools工具的檢測範圍之內，spring.devtools.restart.exclude排除那個目錄下不需要載入。

#新增那個目錄的檔案需要restart
spring.devtools.restart.additional-paths=src/main/java
#排除那個目錄的檔案不需要restart
spring.devtools.restart.exclude=static/**,public/**

四、可以通過設定spring.devtools.restart.enabled=false禁用devtools模組的功能。