4_9.springboot2.x之使用外置servlet容器原理解析

ゝ一纸荒年。 2023-08-17 16:26 136阅读 0赞

***问题概述***  
嵌入式Servlet容器： 应用打成可执行的jar  
**优点**：简单、便携；  
\*\*缺点：\*\*默认不支持JSP、优化定制比较复杂（使用定制器【ServerProperties、自定义WebServerFactoryCustomizer】，自己编写嵌入式Servlet容器的创建工厂【ServletWebServerFactory】）；

如使用jsp：  
*要配置外置的Servlet容器：外面安装Tomcat—应用war包的方式打包；*

**新建项目**  
![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2phdHBlbg_size_16_color_FFFFFF_t_70][]  
**IDEA中配置Webapp文件**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2phdHBlbg_size_16_color_FFFFFF_t_70 1]  
配置web.xml文件

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2phdHBlbg_size_16_color_FFFFFF_t_70 2]  
**配置tomcat**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2phdHBlbg_size_16_color_FFFFFF_t_70 3]  
**测试**  
目录结构  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2phdHBlbg_size_16_color_FFFFFF_t_70 4]  
在application.properties文件中配置springmvc的视图解析：

spring.mvc.view.prefix=/WEB-INF/
    spring.mvc.view.suffix=.jsp

测试：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2phdHBlbg_size_16_color_FFFFFF_t_70 5]

### 步骤 ###

1）、必须创建一个war项目；（利用idea创建好目录结构）

2）、将嵌入式的Tomcat指定为provided；

<dependency>
       <groupId>org.springframework.boot</groupId>
       <artifactId>spring-boot-starter-tomcat</artifactId>
       <scope>provided</scope>
    </dependency>

3）、必须编写一个**SpringBootServletInitializer**的子类，并调用configure方法

public class ServletInitializer extends SpringBootServletInitializer { 
    
       @Override
       protected SpringApplicationBuilder configure(SpringApplicationBuilder application) { 
           //传入SpringBoot应用的主程序
          return application.sources(SpringBoot04WebJspApplication.class);
       }
    
    }

4）、启动服务器就可以使用；

### 原理 ###

\*\*jar包：\*\*执行SpringBoot主类的main方法，启动ioc容器，创建嵌入式的Servlet容器；

\*\*war包：\*\*启动服务器，**服务器启动SpringBoot应用**【SpringBootServletInitializer】，启动ioc容器；

**servlet3.0规范：**（8.2.4 Shared libraries / runtimes pluggability：）  
规则：

1）、服务器启动（web应用启动）会创建当前web应用里面每一个jar包里面ServletContainerInitializer实例：

2）、ServletContainerInitializer的实现放在jar包的META-INF/services文件夹下，有一个名为javax.servlet.ServletContainerInitializer的文件，内容就是ServletContainerInitializer的实现类的全类名

3）、还可以使用@HandlesTypes，在应用启动的时候加载我们感兴趣的类；

### 流程 ###

\*\***1）、启动Tomcat  
2）、\\org\\springframework\\spring-web\\5.1.9.RELEASE\\spring-web-5.1.9.RELEASE.jar!\\META-INF\\services\\javax.servlet.ServletContainerInitializer  
Spring的web模块里面有这个文件：org.springframework.web.SpringServletContainerInitializer  
3）、SpringServletContainerInitializer将@HandlesTypes(WebApplicationInitializer.class)标注的所有这个类型的类都传入到onStartup方法的Set<Class<?>>；为这些WebApplicationInitializer类型的类创建实例；  
4）、每一个WebApplicationInitializer都调用自己的onStartup；**  
点进**WebApplicationInitializer**查看：  
![20190928182657302.png][]  
5）、相当于我们的SpringBootServletInitializer的类会被创建对象，并执行onStartup方法  
6）、SpringBootServletInitializer实例执行onStartup的时候会createRootApplicationContext；创建容器  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2phdHBlbg_size_16_color_FFFFFF_t_70 6]

protected WebApplicationContext createRootApplicationContext(ServletContext servletContext) { 
     //1、创建SpringApplicationBuilder
    		SpringApplicationBuilder builder = createSpringApplicationBuilder();
    		builder.main(getClass());
    		ApplicationContext parent = getExistingRootWebApplicationContext(servletContext);
    		if (parent != null) { 
    			this.logger.info("Root context already created (using as parent).");
    			servletContext.setAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE, null);
    			builder.initializers(new ParentContextApplicationContextInitializer(parent));
    		}
    		builder.initializers(new ServletContextApplicationContextInitializer(servletContext));
    		builder.contextClass(AnnotationConfigServletWebServerApplicationContext.class);
    		 //调用configure方法，子类重写了这个方法，将SpringBoot的主程序类传入了进来
    		builder = configure(builder);
    		builder.listeners(new WebEnvironmentPropertySourceInitializer(servletContext));
    		//使用builder创建一个Spring应用
    		SpringApplication application = builder.build();
    		if (application.getAllSources().isEmpty()
    				&& AnnotationUtils.findAnnotation(getClass(), Configuration.class) != null) { 
    			application.addPrimarySources(Collections.singleton(getClass()));
    		}
    		Assert.state(!application.getAllSources().isEmpty(),
    				"No SpringApplication sources have been defined. Either override the "
    						+ "configure method or add an @Configuration annotation");
    		// Ensure error pages are registered
    		if (this.registerErrorPageFilter) { 
    			application.addPrimarySources(Collections.singleton(ErrorPageFilterConfiguration.class));
    		}
    		//启动Spring应用
    		return run(application);
    	}

7）、Spring的应用就启动并且创建IOC容器

public ConfigurableApplicationContext run(String... args) { 
       StopWatch stopWatch = new StopWatch();
       stopWatch.start();
       ConfigurableApplicationContext context = null;
       FailureAnalyzers analyzers = null;
       configureHeadlessProperty();
       SpringApplicationRunListeners listeners = getRunListeners(args);
       listeners.starting();
       try { 
          ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                args);
          ConfigurableEnvironment environment = prepareEnvironment(listeners,
                applicationArguments);
          Banner printedBanner = printBanner(environment);
          context = createApplicationContext();
          analyzers = new FailureAnalyzers(context);
          prepareContext(context, environment, listeners, applicationArguments,
                printedBanner);
           
           //刷新IOC容器
          refreshContext(context);
          afterRefresh(context, applicationArguments);
          listeners.finished(context, null);
          stopWatch.stop();
          if (this.logStartupInfo) { 
             new StartupInfoLogger(this.mainApplicationClass)
                   .logStarted(getApplicationLog(), stopWatch);
          }
          return context;
       }
       catch (Throwable ex) { 
          handleRunFailure(context, listeners, analyzers, ex);
          throw new IllegalStateException(ex);
       }
    }

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