The main process of processing HTTP requests in Tomcat is as follows

1. When Tomcat receives a client request, it will hand over the request CoyoteAdapterfor processing.
2. CoyoteAdapterConnectorFind the corresponding sum based on the request method (GET, POST, etc.) and URL Processor.
3. ProcessorIt is a Servlet container that is responsible for creating and maintaining Servlet objects, processing HTTP requests, and returning the generated responses to the client.
4. ProcessorThe Servlet instance will be created and initialized when called StandardWrapperValve, and its corresponding life cycle method will be called to process the request and generate a response.

The following is StandardWrapperValvea code snippet that handles Servlet requests:

public final class StandardWrapperValve extends ValveBase {

    public void invoke(Request request, Response response) throws IOException, ServletException {

        ......
        // 在这里获取到对应的Servlet对象
        Servlet servlet = wrapper.allocate();
        
        try {
            // 初始化Servlet并调用相应的生命周期方法
            request.setServletPath(wrapper.getServletPath());
            request.setAttribute(Globals.SERVLET_MAPPING_ATTR, wrapper.getServletMapping().getMatchValue());
            support.fireInstanceEvent(InstanceEvent.BEFORE_INIT_EVENT, servlet);
            servlet.init(config);
            support.fireInstanceEvent(InstanceEvent.AFTER_INIT_EVENT, servlet);
            pipeline.invoke(request, response);
            support.fireInstanceEvent(InstanceEvent.BEFORE_DESTROY_EVENT, servlet);
        } finally {
            // 销毁Servlet实例
            if (servlet != null) {
                wrapper.deallocate(servlet);
            }
            request.recycle();
            response.recycle();
        }
        
    }
}

In this code snippet we can see:

1. StandardWrapperValveIt is an Valveimplementation class used to process Servlet requests in Tomcat's request processing process.
2. In invokethe method, StandardWrapperValvefirst find the corresponding Servletobject based on the URL path information (servlet path) contained in the request.
3. Then, the HTTP request is processed and the response is generated StandardWrapperValveby calling Servletthe life cycle methods ( init(), service()etc.).
4. Finally, in finallythe block, the Servlet container will call servletthe destroy()method to destroy the Servlet instance.

It should be noted that this is just a brief example of Tomcat's Servlet request processing logic. The actual code implementation may be more complex than this and involve multiple modules and classes working together.