I. Introduction
Last article talked about SpingBoot the birth of the historical background and context of the evolution of technology, and through the source explained SpringBoot including how to configure web.xml eliminating the principle of how to achieve zero configuration. This article last article, by demo demonstrates how SpringBoot is built and implemented tomcat java-based Servlet initialization and configuration of SpringBoot startup process.
Second, based on the configuration web.xml java implementation
Configure content SpringMVC traditional framework of web.xml
. 1 < Web-App > 2 <-! Initialization Spring context -> . 3 < listener > . 4 < listener-class > org.springframework.web.context.ContextLoaderListener </ listener-class > . 5 </ listener > . 6 <! - Specifies Spring configuration file > - . 7 < context-param > . 8 < param-name > the contextConfigLocation </ param-name > . 9 < param-value >/WEB-INF/app-context.xml</param-value> 10 </context-param> 11 <!-- 初始化DispatcherServlet --> 12 <servlet> 13 <servlet-name>app</servlet-name> 14 <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> 15 <init-param> 16 <param-name>contextConfigLocation</param-name> 17 <param-value></param-value> 18 </init-param> 19 <load-on-startup>1</load-on-startup> 20 </servlet> 21 <servlet-mapping> 22 <servlet-name>app</servlet-name> 23 <url-pattern>/app/*</url-pattern> 24 </servlet-mapping> 25 </web-app>
View Spring official document https://docs.spring.io/spring/docs/5.0.14.RELEASE/spring-framework-reference/web.html#spring-web
Documents given example of how to use java code to achieve web.xml configuration
. 1 public class MyWebApplicationInitializer the implements WebApplicationInitializer { 2 . 3 @Override . 4 public void OnStartup (the ServletContext servletCxt) { . 5 . 6 // the Load Spring Web Configuration file application . 7 // by annotation initializes Spring context . 8 AnnotationConfigWebApplicationContext AC = new new AnnotationConfigWebApplicationContext (); . 9 // Register spring configuration type (xml replace the traditional items of configuration) 10 ac.register (AppConfig. class ); . 11 ac.refresh (); 12 13 // Create and register the DispatcherServlet 14 //基于java代码的方式初始化DispatcherServlet 15 DispatcherServlet servlet = new DispatcherServlet(ac); 16 ServletRegistration.Dynamic registration = servletCxt.addServlet("app", servlet); 17 registration.setLoadOnStartup(1); 18 registration.addMapping("/app/*"); 19 } 20 }
Achieve visible through the example of java-based web.xml
Third, the code that implements simple version SpringBoot
1, the project directory structure
2, pom.xml dependence
1 <?xml version="1.0" encoding="UTF-8"?> 2 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 3 xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> 4 <modelVersion>4.0.0</modelVersion> 5 <groupId>com.shf</groupId> 6 <artifactId>spring-tomcat</artifactId> 7 <version>0.0.1-SNAPSHOT</version> 8 <name>spring-tomcat</name> 9 <description>Demo project for Spring Boot</description> 10 11 <properties> 12 <java.version>1.8</java.version> 13 </properties> 14 15 <dependencies> 16 <dependency> 17 <groupId>org.springframework</groupId> 18 <artifactId>spring-web</artifactId> 19 <version>5.0.8.RELEASE</version> 20 </dependency> 21 <dependency> 22 <groupId>org.apache.tomcat.embed</groupId> 23 <artifactId>tomcat-embed-core</artifactId> 24 <version>8.5.32</version> 25 </dependency> 26 <dependency> 27 <groupId>org.springframework</groupId> 28 <artifactId>spring-context</artifactId> 29 <version>5.0.8.RELEASE</version> 30 </dependency> 31 <dependency> 32 <groupId>org.springframework</groupId> 33 <artifactId>spring-webmvc</artifactId> 34 <version>5.0.8.RELEASE</version> 35 </dependency> 36 </dependencies> 37 38 <build> 39 <plugins> 40 <plugin> 41 <groupId>org.springframework.boot</groupId> 42 <artifactId>spring-boot-maven-plugin</artifactId> 43 </plugin> 44 </plugins> 45 </build> 46 47 </project>
3, tomcat instance initialization
1 package com.shf.tomcat.application; 2 3 4 import org.apache.catalina.LifecycleException; 5 import org.apache.catalina.startup.Tomcat; 6 7 import javax.servlet.ServletException; 8 9 /** 10 * 描述：初始化tomcat 11 * 12 * @Author shf 13 * @Date 2019/5/26 14:58 14 * @Version V1.0 15 **/ 16 public class SpringApplication { 17 public static void run(){ 18 // create an instance of tomcat 19 Tomcat tomcat = new new Tomcat (); 20 // set tomcat port 21 tomcat.setPort (8000 ); 22 the try { 23 // here just specify what webapp, let tomcat know that this is a web project 24 tomcat.addWebapp ( "/", "D: \\" ); 25 // start Tomcat 26 is tomcat.start (); 27 tomcat.getServer () the await ();. 28 } the catch (LifecycleException E) { 29 E .printStackTrace (); 30 }catch (ServletException e) { 31 e.printStackTrace(); 32 } 33 } 34 }
4、AppConfig.java
This class is mainly to achieve the Spring configuration, based on java achieve spring xml configuration
1 package com.shf.tomcat.web; 2 3 import org.springframework.context.annotation.Bean; 4 import org.springframework.context.annotation.ComponentScan; 5 import org.springframework.context.annotation.Configuration; 6 7 import javax.servlet.http.HttpServlet; 8 9 /** 10 * 描述：java代码实现类似于spring-context.xml的配置 11 * 12 * @Author shf 13 * @Date 2019/5/22 21:28 14 * @Version V1.0 15 **/ 16 @Configuration 17 @ComponentScan("com.shf.tomcat") 18 public class AppConfig extends HttpServlet { 19 @Bean 20 public String string(){ 21 return new String("hello"); 22 } 23 }
5、MyWebApplicationInitializer.java
It is worth saying, this class is java based web.xml configuration
1 package com.shf.tomcat.web; 2 3 import org.springframework.web.WebApplicationInitializer; 4 import org.springframework.web.context.support.AnnotationConfigWebApplicationContext; 5 import org.springframework.web.servlet.DispatcherServlet; 6 7 import javax.servlet.ServletContext; 8 import javax.servlet.ServletException; 9 import javax.servlet.ServletRegistration; 10 11 /** 12 * 描述：WebApplicationInitializer实现web.xml的配置 13 * 14 * @Author shf 15 * @date 2019/5/22 21:25 16 * @Version V1.0 . 17 * * / 18 is public class MyWebApplicationInitializer the implements WebApplicationInitializer { . 19 public void OnStartup (where servletContext the ServletContext) throws ServletException { 20 is System.out.println ( "Initialization MyWebApplicationInitializer " ); 21 is // by way annotation context initialization Spring 22 is AnnotationConfigWebApplicationContext AC = new new AnnotationConfigWebApplicationContext (); 23 is // register class spring configuration (conventional configuration replace the item xml) 24 ac.register(AppConfig.class); 25 // ac.refresh(); 26 27 // Create and register the DispatcherServlet 28 //基于java代码的方式初始化DispatcherServlet 29 DispatcherServlet servlet = new DispatcherServlet(ac); 30 ServletRegistration.Dynamic registration = servletContext.addServlet("/", servlet); 31 registration.setLoadOnStartup(1); 32 registration.addMapping("/*"); 33 } 34 }
6、MySpringServletContainerInitializer.java
This class last article has been said very clearly
1 package com.shf.tomcat.web; 2 3 import org.springframework.core.annotation.AnnotationAwareOrderComparator; 4 import org.springframework.util.ReflectionUtils; 5 import org.springframework.web.WebApplicationInitializer; 6 7 import javax.servlet.ServletContainerInitializer; 8 import javax.servlet.ServletContext; 9 import javax.servlet.ServletException; 10 import javax.servlet.annotation.HandlesTypes; 11 import java.lang.reflect.Modifier; 12 import java.util.LinkedList; 13 import java.util.List; 14 import java.util.Set; 15 16 @HandlesTypes(MyWebApplicationInitializer.class) 17 public class MySpringServletContainerInitializer implements ServletContainerInitializer { 18 public void onStartup(Set<Class<?>> webAppInitializerClasses, ServletContext servletContext) throws ServletException { 19 List<WebApplicationInitializer> initializers = new LinkedList<WebApplicationInitializer>(); 20 21 if (webAppInitializerClasses != null) { 22 for (Class<?> waiClass : webAppInitializerClasses) { 23 if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) && 24 WebApplicationInitializer.class.isAssignableFrom(waiClass)) { 25 try { 26 initializers.add((WebApplicationInitializer) 27 ReflectionUtils.accessibleConstructor(waiClass).newInstance()); 28 } 29 catch (Throwable ex) { 30 throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex); 31 } 32 } 33 } 34 } 35 36 if (initializers.isEmpty()) { 37 servletContext.log("No Spring WebApplicationInitializer types detected on classpath"); 38 return; 39 } 40 41 servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath"); 42 AnnotationAwareOrderComparator.sort(initializers); 43 for (WebApplicationInitializer initializer : initializers) { 44 initializer.onStartup(servletContext); 45 } 46 } 47 }
7、META-INF/services/javax.servlet.ServletContainerInitializer
ServletContainerInitializer implementation class configured in the file
8, the test class
Write a test class
1 package com.shf.tomcat.controller; 2 3 import org.springframework.web.bind.annotation.RequestMapping; 4 import org.springframework.web.bind.annotation.RestController; 5 6 @RestController 7 public class TestController { 8 @RequestMapping("/app/test") 9 public String test(){ 10 System.out.println("--- hello ---"); 11 return "hello"; 12 } 13 }
9, the main class
1 package com.shf.tomcat; 2 3 4 import com.shf.tomcat.application.SpringApplication; 5 6 public class Main { 7 8 public static void main(String[] args) { 9 SpringApplication.run(); 10 } 11 12 }
10, the test
Start the Main method
Browser access: HTTP: // localhost: 8080 / App / the Test
IV Summary
The article describes how to configure web.xml java-based SpringBoot is achieved. In this article we come to know SpringBoot through a demo that is built tomcat and how to achieve zero configuration. In fact, this demo is like SpringBoot framework of a simple version of the basic analog SpringBoot start the process, but the most important difference between the ability SpringBoot --- automatic assembly.
这两篇文章严格来说不应该算是SpringBoot的源码篇，但是笔者认为关于SpringBoot的发展历史、技术演进路线、及SpringBoot的嵌入式tomcat和code-based web.xml配置也是认识SpringBoot重要的一部分。
下一篇文章正式开始SpringBoot的源码阅读之旅。