17.SpringMVC源码分析

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1.服务器启动时的源码分析

  1. 寻找init()

  2. DispatcherServlet类中没有init()，在它的父类中寻找init()

  3. FrameworkServlet类中没有init()，在它的父类中寻找init()

  4. HttpServletBean.init()

  5. HttpServletBean.init() –> HttpServletBean.initServletBean()，但是HttpServletBean.initServletBean()方法体为空，找它的子类对initServletBean()的实现

  6. FrameworkServlet.initServletBean() –> FrameworkServlet.initWebApplicationContext()

  7. FrameworkServlet.initWebApplicationContext() –> FrameworkServlet.onRefresh()，但是FrameworkServlet.onRefresh()方法体为空，找它的子类对onRefresh()的实现

  8. DispatcherServlet.onRefresh() –> DispatcherServlet.initStrategies()

  9. DispatcherServlet.initStrategies()调用了initHandlerMappings(), initHandlerAdapters(), initViewResolvers()等方法进行了初始化

DispatcherServlet.java

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public class DispatcherServlet extends FrameworkServlet {
    // ...

    @Override
	protected void onRefresh(ApplicationContext context) {
		initStrategies(context);
	}

    protected void initStrategies(ApplicationContext context) {
		initMultipartResolver(context);
		initLocaleResolver(context);
		initThemeResolver(context);
		initHandlerMappings(context);
		initHandlerAdapters(context);
		initHandlerExceptionResolvers(context);
		initRequestToViewNameTranslator(context);
		initViewResolvers(context);
		initFlashMapManager(context);
	}

    // ...
}

FrameworkServlet.java

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public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {
    // ...

    @Override
	protected final void initServletBean() throws ServletException {
		// ...
		try {
			this.webApplicationContext = initWebApplicationContext();
			// ...
		}
		// ...
	}

    protected WebApplicationContext initWebApplicationContext() {
		// ...

		if (!this.refreshEventReceived) {
			// Either the context is not a ConfigurableApplicationContext with refresh
			// support or the context injected at construction time had already been
			// refreshed -> trigger initial onRefresh manually here.
			synchronized (this.onRefreshMonitor) {
				onRefresh(wac);
			}
		}

		// ...
	}

    protected void onRefresh(ApplicationContext context) {
		// For subclasses: do nothing by default.
	}

    // ...
}

HttpServletBean.java

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public abstract class HttpServletBean extends HttpServlet implements EnvironmentCapable, EnvironmentAware {
    // ...

    @Override
	public final void init() throws ServletException {
        // ...

		// Let subclasses do whatever initialization they like.
		initServletBean();
	}

    protected void initServletBean() throws ServletException {

	}

    // ...
}

2.当接收用户请求时的源码分析

  1. 寻找service()

  2. DispatcherServlet类中没有service()，在它的父类中寻找service()

  3. FrameworkServlet.service()

  4. FrameworkServlet.service() –> FrameworkServlet.processRequest()

  5. FrameworkServlet.processRequest() –> FrameworkServlet.doService()，但是FrameworkServlet.doService()方法是一个抽象方法，找它的子类对doService()的实现

  6. DispatcherServlet.doService() –> DispatcherServlet.doDispatch()

  7. DispatcherServlet.doDispatch() –> org.springframework.web.servlet.HandlerAdapter.handle()和DispatcherServlet.processDispatchResult()

  8. DispatcherServlet.processDispatchResult() –> DispatcherServlet.render()

  9. DispatcherServlet.render() –> org.springframework.web.servlet.View.render()

FrameworkServlet.java

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public abstract class FrameworkServlet extends HttpServletBean implements ApplicationContextAware {
    // ...

    @Override
	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
		if (httpMethod == HttpMethod.PATCH || httpMethod == null) {
			processRequest(request, response);
		}
		else {
			super.service(request, response);
		}
	}

    protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		// ...

		try {
			doService(request, response);
		}
		
        // ...
	}

    protected abstract void doService(HttpServletRequest request, HttpServletResponse response)
			throws Exception;

    // ...
}

DispatcherServlet.java

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public class DispatcherServlet extends FrameworkServlet {
    // ...

    @Override
	protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
		// ...

		try {
			doDispatch(request, response);
		}
		
        // ...
	}

    protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
		// ...

		try {
			ModelAndView mv = null;
			// ...

			try {
				// ...

                // Determine handler adapter for the current request.
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                // ...

				// Actually invoke the handler.
                // 执行Controller里面的方法
				mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

				// ...
			}
			// ...
            // 转发和渲染
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		// ...
	}

    private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
			@Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
			@Nullable Exception exception) throws Exception {

		// ...

		// Did the handler return a view to render?
		if (mv != null && !mv.wasCleared()) {
            // 渲染
			render(mv, request, response);
			// ...
		}
		
        // ...
	}

    protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception {
		// ...

		try {
			// ...
            // 渲染
			view.render(mv.getModelInternal(), request, response);
		}
		
        // ...
	}

    // ...
}