【SpringMVC源码解析】 ServletContainerInitializer && SpringMVC源码入口解析

淩亂°似流年 2023-07-11 14:00 66阅读 0赞

# 1 ServletContainerInitializer #

在web容器启动时为提供给第三方组件机会做一些初始化的工作，servlet规范(JSR356)中通过ServletContainerInitializer实现此功能。每个框架要使用ServletContainerInitializer就必须在对应的jar包的META-INF/services 目录创建一个名为javax.servlet.ServletContainerInitializer的文件，文件内容指定具体的ServletContainerInitializer实现类，那么，当web容器启动时就会运行这个初始化器做一些组件内的初始化工作。

(1) 创建JAVA-WEB项目  
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(2) 创建接口及接口相关类

public interface ZrsService { 
    
    }
    
    public interface ZrsServiceExtend extends ZrsService { 
    
    }
    
    public abstract class AbstractZrsService implements ZrsService { 
    
    }
    
    public class ZrsServicImpl implements ZrsService { 
    
    }

(3) 创建ServletContainerInitializer接口实现类

/** * @Description: HandlesTypes，获取当前接口所有相关的类 * @Auther: zhurongsheng * @Date: 2020/3/5 15:14 */
    @HandlesTypes(value = { ZrsService.class})
    public class ZrsServletContainerInitializer implements ServletContainerInitializer { 
        @Override
        public void onStartup(Set<Class<?>> classs, ServletContext servletContext) throws ServletException { 
            System.out.println("################################");
            for (Class clazz:classs){ 
                System.out.println(clazz);
            }
        }
    }

(4) 在META-INF/services 下创建 javax.servlet.ServletContainerInitializer

com.servlet.ZrsServletContainerInitializer

(5) 工程结构  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 1]  
(6) 启动tomcat，发现调用了ZrsServletContainerInitializer onStartup方法  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 2]

# 2 SpringMVC环境准备 #

(1) 创建maven 工程  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 3]

(2) 删除webapp下所有\*.xml文件  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 4]  
(3) 引入依赖

<dependencies>
      <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>5.0.6.RELEASE</version>
      </dependency>
      
      <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
        <scope>provided</scope>
      </dependency>
      <dependency>
        <groupId>org.projectlombok</groupId>
        <artifactId>lombok</artifactId>
        <version>1.18.6</version>
      </dependency>
    </dependencies>
    <build>
      <plugins>
        <plugin>
          <artifactId>maven-compiler-plugin</artifactId>
          <configuration>
            <source>1.8</source>
            <target>1.8</target>
            <encoding>UTF-8</encoding>
            <compilerArguments>
              <extdirs>${ basedir}/src/main/webapp/WEB-INF/lib</extdirs>
            </compilerArguments>
          </configuration>
        </plugin>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-war-plugin</artifactId>
          <version>2.4</version>
          <configuration>
            <failOnMissingWebXml>false</failOnMissingWebXml>
          </configuration>
        </plugin>
      </plugins>
    </build>

3 查看spring-web包  
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# 4 初步分析SpringServletContainerInitializer #

(1) 源码分析，初始化WebApplicationInitializer接口的bean，并且调用WebApplicationInitializer实现类的onStartup方法

/** * 获取WebApplicationInitializer接口的所有类型 */
    @HandlesTypes(WebApplicationInitializer.class)
    public class SpringServletContainerInitializer implements ServletContainerInitializer { 
        
        @Override
        public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
                throws ServletException { 
            //1 创建存储WebApplicationInitializer的List
            List<WebApplicationInitializer> initializers = new LinkedList<>();
            if (webAppInitializerClasses != null) { 
                for (Class<?> waiClass : webAppInitializerClasses) { 
                    // Be defensive: Some servlet containers provide us with invalid classes,
                    // no matter what @HandlesTypes says...
                    if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
                            WebApplicationInitializer.class.isAssignableFrom(waiClass)) { 
                        try { 
                            //2 用反射机制创建WebApplicationInitializer实现类并且添加到List中
                            initializers.add((WebApplicationInitializer)
                                    ReflectionUtils.accessibleConstructor(waiClass).newInstance());
                        }
                        catch (Throwable ex) { 
                            throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
                        }
                    }
                }
            }
            if (initializers.isEmpty()) { 
                servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
                return;
            }
            servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
            AnnotationAwareOrderComparator.sort(initializers);
            //3 调用WebApplicationInitializerde的onStartup方法
            for (WebApplicationInitializer initializer : initializers) { 
                initializer.onStartup(servletContext);
            }
        }
    }

(2)WebApplicationInitializer接口实现类分析 AbstractContextLoaderInitializer  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 6]

(3) WebApplicationInitializer接口实现类分析 AbstractDispatcherServletInitializer  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 7]

(4) WebApplicationInitializer接口实现类分析 AbstractAnnotationConfigDispatcherServletInitializer

public abstract class AbstractAnnotationConfigDispatcherServletInitializer
            extends AbstractDispatcherServletInitializer { 
        /** * 创建RootApplicationContext */
        @Override
        @Nullable
        protected WebApplicationContext createRootApplicationContext() { 
            Class<?>[] configClasses = getRootConfigClasses();
            if (!ObjectUtils.isEmpty(configClasses)) { 
                AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
                context.register(configClasses);
                return context;
            }
            else { 
                return null;
            }
        }
        /** * 创建ServletApplicationContext */
        @Override
        protected WebApplicationContext createServletApplicationContext() { 
            AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
            Class<?>[] configClasses = getServletConfigClasses();
            if (!ObjectUtils.isEmpty(configClasses)) { 
                context.register(configClasses);
            }
            return context;
        }
        /** * 获取RootApplicationContext 配置类 */
        @Nullable
        protected abstract Class<?>[] getRootConfigClasses();
        /** * 获取ServletApplicationContext配置类 */
        @Nullable
        protected abstract Class<?>[] getServletConfigClasses();
    }

(5) ServletApplicationContext和RootApplicationContext区别如下图：  
ServletApplicationContext：负责Controller 视图相关的…  
RootApplicationContext：负责Service、数据库相关的…  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 8]

# 5 AbstractAnnotationConfigDispatcherServletInitializer作用解析 #

## 5.1 给ServletWebApplicationContext添加ServletConfig配置文件 ##

(1) 创建配置文件

/** * @Description: ServletConfig配置文件,ServleWebApplicationContext仅包含Controller方面的注解 * @Auther: zhurongsheng * @Date: 2020/3/6 14:44 */
    @ComponentScan(value="com.spring",includeFilters={ 
            @ComponentScan.Filter(type= FilterType.ANNOTATION,classes={ Controller.class, RestController.class})
    },useDefaultFilters=false)
    public class ZrsServletConfig { 
    
    
    }

(2) 创建Controller

@RestController
    @RequestMapping("/hello")
    public class HelloController { 
        @GetMapping("")
        public String hello(){ 
            return "hello spring mvc";
        }
    }

(3) ZrsWebInitializer

/** * @Description: web容器启动创建时的对象 * @Auther: zhurongsheng * @Date: 2020/3/5 23:20 */
    public class ZrsWebInitializer extends AbstractAnnotationConfigDispatcherServletInitializer { 
        /** * RootApplicationContext 配置文件 */
        @Override
        protected Class<?>[] getRootConfigClasses() { 
            return new Class<?>[]{ };
        }
        /** * ServletApplicationContext 配置文件 */
        @Override
        protected Class<?>[] getServletConfigClasses() { 
            System.out.println("ZrsWebInitializer invoke getServletConfigClasses");
            return new Class<?>[]{  ZrsServletConfig.class};
        }
        /** *拦截请求(静态资源、js、css.......) */
        @Override
        protected String[] getServletMappings() { 
            return new String[]{ "/"};
        }
    }

(4) 启动tomcat  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 9]  
(5) 访问URL  
http://localhost:8080/spring\_web\_war/hello  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 10]

## 5.2 @EnableWebMvc注解，等于在xml中配置 ##

<mvc:default-servlet-handler/>
        
        <mvc:annotation-driven></mvc:annotation-driven>

## 5.3 WebMvcConfigurer接口代替了springmvc在xml中的配置 ##

(1) 视图解析器  
修改ZrsServletConfig配置文件

@ComponentScan(value="com.spring",includeFilters={ 
            @ComponentScan.Filter(type= FilterType.ANNOTATION,classes={ Controller.class, RestController.class})
    },useDefaultFilters=false)
    @EnableWebMvc
    public class ZrsServletConfig implements WebMvcConfigurer { 
        /** * 配置视图解析器 */
        @Override
        public void configureViewResolvers(ViewResolverRegistry registry) { 
            registry.jsp("/WEB-INF/pages/",".jsp");
        }
    }

修改controller

@Controller
    @RequestMapping("/hello")
    public class HelloController { 
        @GetMapping("")
        public String hello(){ 
            return "hello spring mvc";
        }
        @GetMapping("/page")
        public String page(){ 
            return "helloworld";
        }
    }

创建jsp  
![在这里插入图片描述][20200306192947671.png]  
启动tomcat  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 11]

(2) 配置静态资源

创建jsp、css：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 12]

![在这里插入图片描述][20200306193032548.png]  
![在这里插入图片描述][20200306193035784.png]  
启动tomcat：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 13]

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[20200306192947671.png]: https://img-blog.csdnimg.cn/20200306192947671.png
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[20200306193032548.png]: https://img-blog.csdnimg.cn/20200306193032548.png
[20200306193035784.png]: https://img-blog.csdnimg.cn/20200306193035784.png
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