springmvc源码解析

「爱情、让人受尽委屈。」 2022-04-10 02:23 261阅读 0赞

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dmbG92ZWphdmE_size_16_color_FFFFFF_t_70][]

总结：

首先请求进入DispatcherServlet 由DispatcherServlet 从HandlerMappings中提取对应的Handler  
   
 此时只是获取到了对应的Handle，然后得去寻找对应的适配器，即：HandlerAdapter  
  拿到对应HandlerAdapter时，这时候开始调用对应的Handler处理业务逻辑了（这时候实际上已经执行完了我们 的Controller） 执行完成之后返回一个ModeAndView  
  
 这时候交给我们的ViewResolver通过视图名称查找出对应的视图然后返回  
  最后 渲染视图 返回渲染后的视图 -->响应请求

**实例：**

在pom.xml文件上添加spring-mvc的依赖

<dependencies>
        
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>5.0.8.RELEASE</version>
        </dependency>
        
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>

添加App类
    import org.springframework.context.annotation.ComponentScan;
    import org.springframework.context.annotation.Configuration;
    
    /**
     * @author wufei
     * @create 2018-12-24 9:37
     **/
    @ComponentScan("com.wf.spring.mvc")
    @Configuration
    public class App {
    }

添加DispatcherServlet类

/**
     * 添加DispatcherServlet
     * @author wufei
     * @create 2018-12-24 9:47
     **/
    public class MyWebApplicationInitializer implements WebApplicationInitializer {
        @Override
        public void onStartup(ServletContext servletCxt) {
            // Load Spring web application configuration
            AnnotationConfigWebApplicationContext ac = new AnnotationConfigWebApplicationContext();
            ac.register(AppConfig.class);
            ac.refresh();
    
            // Create and register the DispatcherServlet
            DispatcherServlet servlet = new DispatcherServlet(ac);
            ServletRegistration.Dynamic registration = servletCxt.addServlet("app", servlet);
            registration.setLoadOnStartup(1);
            registration.addMapping("/app/*");
    
        }
    }

/**
     * 第一种方式注册controller
     * 使用bean的形成注册controller
     * @author wufei
     * @create 2018-12-24 9:58
     **/
    @Component("/test")
    public class BeanController implements Controller{
        @Override
        public ModelAndView handleRequest(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse) {
            System.out.println("test");
            return null;
        }
    }

/**
     * 第二种方式注册controller
     * annotation形式注册controller
     * RequestMappingHandlerMapping
     * @author wufei
     * @create 2018-12-24 15:10
     **/
    @Controller
    public class AnnotationController {
    
        @RequestMapping("/test1")
        public String test(){
            System.out.println("test1");
            return "test1";
        }
    }

**源码分析：**

首先我们看下DispatcherServlet继承关系图：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dmbG92ZWphdmE_size_16_color_FFFFFF_t_70 1][]

从图中可以看出DispatcherServlet最终继承的是个HttpServlet，即DispatcherServlet就是个Servlet。由此我们可以找到Servlet的doGet、doPost、service重要方法。在FrameworkServlet类中可以看到

protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
        if (httpMethod != HttpMethod.PATCH && httpMethod != null) {
            super.service(request, response);
        } else {
            this.processRequest(request, response);
        }
    
    }
    
    protected final void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.processRequest(request, response);
    }
    
    protected final void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.processRequest(request, response);
    }

从三个方法上可以看出，都是调用了processRequest(request, response);方法，然后我们继续跟踪processRequest方法上

我们可以看到doService方法

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dmbG92ZWphdmE_size_16_color_FFFFFF_t_70 2][]

该方法是个抽象方法，由DispatcherServlet类实现该方法的具体逻辑。发现有个重要的关键代码方法this.doDispatch(request, response);

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dmbG92ZWphdmE_size_16_color_FFFFFF_t_70 3][]

进入doDispatch方法里面

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dmbG92ZWphdmE_size_16_color_FFFFFF_t_70 4][]

看到两个最重要的方法，getHandler（处理器）和getHandlerAdapter（适配器）

**问题1 handler从哪来的呢**

我们先查看getHandler方法里面的代码

@Nullable
    protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        if (this.handlerMappings != null) {
            Iterator var2 = this.handlerMappings.iterator();
            while(var2.hasNext()) {
                HandlerMapping hm = (HandlerMapping)var2.next();
                if (this.logger.isTraceEnabled()) {
                    this.logger.trace("Testing handler map [" + hm + "] in DispatcherServlet with name '" + this.getServletName() + "'");
                }
    
                HandlerExecutionChain handler = hm.getHandler(request);
                if (handler != null) {
                    return handler;
                }
            }
        }
    
        return null;
    }
    是在迭代handlerMappings，而handlerMappings是个List集合

@Nullable
    private List<HandlerMapping> handlerMappings;

handlerMapping存放两个值，一个是org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping，一个是org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dmbG92ZWphdmE_size_16_color_FFFFFF_t_70 5][]

**问题2 handlerMapping是什么？**

我们端个点，查看下具体是什么

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dmbG92ZWphdmE_size_16_color_FFFFFF_t_70 6][]

如图所示：是两个我们不认识的东西，我们继续往下看，

HandlerExecutionChain handler = hm.getHandler(request);
    if (handler != null) {
        return handler;
    }

从mappings获取一个handler，然后返回了。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dmbG92ZWphdmE_size_16_color_FFFFFF_t_70 7][]

我们发现 handler就是我们的controll类的方法，我们以Bean的形式注册的Controller 可以从这个BeanNameUrlHandlerMapping里面 获取到对应的Handler ; 这里 我们是不是对于这个HandlerMapping有了懵懂的了解了

下面我们以Annotation方式注册的Controller，就会被第二个RequestMappingHandlerMapping获取对应的handler。如图所示：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dmbG92ZWphdmE_size_16_color_FFFFFF_t_70 8][]

**问题3 什么是适配器**

**首先我们跟踪下代码**

HandlerAdapter ha = this.getHandlerAdapter(mappedHandler.getHandler());

protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
        if (this.handlerAdapters != null) {
            Iterator var2 = this.handlerAdapters.iterator();
    
            while(var2.hasNext()) {
                HandlerAdapter ha = (HandlerAdapter)var2.next();
                if (this.logger.isTraceEnabled()) {
                    this.logger.trace("Testing handler adapter [" + ha + "]");
                }
    
                if (ha.supports(handler)) {
                    return ha;
                }
            }
        }
    
        throw new ServletException("No adapter for handler [" + handler + "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
    }

从代码上可以看出是迭代handlerAdapters，而这个从哪获取到的呢？也是从配置文件上获取的DispatcherServlet.properties

org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
       org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
       org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter

使用Annotation方式注册的Controller使用的是RequestMappingHandlerAdapter适配器

![20181224180023611.png][]

使用bean的形成注册controller使用的是SimpleControllerHandlerAdapter适配器

最后执行mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); 执行业务逻辑了。输出了test1

![20181224180740192.png][]

然后返回mv，mv就是试图了，然后渲染页面。

**适配器就是对应不同的handler有不同的解决方案**

**总结 **  
其实我们的SpringMVC关键的概念就在于Handler（处理器） 和Adapter(适配器)  
  通过一个关键的HandlerMappings 找到合适处理你的Controller的Handler 然后再通过HandlerAdapters找到一 个合适的HandlerAdapter 来执行Handler即Controller里面的逻辑。 最后再返回ModlAndView...

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[20181224180023611.png]: /images/20220403/4ee3808eae9d44ebb9881115d0189a6a.png
[20181224180740192.png]: /images/20220403/b0c30f687587469a89d8368e5ac6132a.png