1. What is Spring MVC? Briefly introduce your understanding of spring MVC?

Spring MVC is a lightweight web framework based on Java that implements the request driven type of MVC design pattern. By separating Model, View and Controller, it decouples the responsibilities of the web layer, divides complex web applications into logical parts, simplifies development, reduces errors, and facilitates cooperation between developers in the group.

2. Spring MVC process?

(1) The user sends a request to the front-end controller DispatcherServlet;
(2) After the DispatcherServlet receives the request, it calls the HandlerMapping processor mapper to request to obtain a Handle;
(3) The processor mapper finds the specific processor according to the request url, generates the processor object and the processor interceptor (if any), and returns them to the DispatcherServlet;
(4) DispatcherServlet calls the HandlerAdapter processor adapter;
(5) The HandlerAdapter calls the specific processor (Handler, also called the back-end controller) through adaptation;
(6) The handler returns to ModelAndView after execution;
(7) The HandlerAdapter returns the Handler execution result ModelAndView to the DispatcherServlet;
(8) DispatcherServlet transmits ModelAndView to ViewResolver view parser for parsing;
(9) The ViewResolver returns the specific View after resolution;
(10) DispatcherServlet renders the view (that is, fills the model data into the view)
(11) DispatcherServlet responds to the user.

3. Advantages of Springmvc:

(1) It can support various view technologies, not limited to JSP;
(2) Integration with Spring framework (such as IoC container, AOP, etc.);
(3) Clear role assignment: front-end controller (dispatcherServlet), request to processor mapping (handlerMapping), processor adapter (HandlerAdapter), view resolver (ViewResolver).
(4) Support mapping strategies for various request resources.

4. What are the main components of Spring MVC?

(1) Front end controller DispatcherServlet (no programmer development required)
Function: Receiving request and response results is equivalent to a repeater. The DispatcherServlet reduces the coupling between other components.
(2) Processor mapper HandlerMapping (no programmer development required)
Function: Find the handler according to the requested URL
(3) Processor Adapter HandlerAdapter
Note: The handler should be written according to the rules required by the HandlerAdapter, so that the adapter HandlerAdapter can correctly execute the handler.
(4) Processor Handler (need programmer to develop)
(5) ViewResolver (not developed by programmers)
Function: analyze the view, and convert it into a real view according to the logical name of the view
(6) View (programmer needs to develop jsp)
View is an interface whose implementation class supports different view types (jsp, freemarker, pdf, etc.)

6. How does Spring MVC set redirection and forwarding?

(1) Forward: add “forward:” before the return value, such as “forward: user. do? Name=method4”
(2) Redirect: add “redirect:” before the return value, such as "redirect: http://www.baidu.com “

7. How does SpringMvc and AJAX call each other?

Through the Jackson framework, you can directly convert objects in Java into Json objects that Js can recognize. The specific steps are as follows:
(1) Join Jackson.jar
(2) Configure the mapping of json in the configuration file
(3) In accepting Ajax methods, you can directly return Object, List, etc., but the @ ResponseBody annotation should be added in front of the method.

8. How to solve the problem of Chinese garbled code in POST requests, and how to deal with GET?

(1) To solve the problem of garbled post requests:
Configure a CharacterEncodingFilter in web.xml and set it to utf-8;
(2) There are two ways to solve the problem of garbled Chinese parameters in the get request:
① Modify the tomcat configuration file to add a code consistent with the project code, as follows:
② Another method is to re code parameters:
String userName=new String (request. getParamter (“userName”). getBytes (“ISO8859-1”), “utf-8”)
ISO8859-1 is the default encoding of tomcat. The content encoded by tomcat needs to be encoded as utf-8.

9. Spring MVC exception handling?

Answer: You can throw exceptions to the Spring framework for processing; We just need to configure a simple exception handler and add a view page to the exception handler.

10. Is SpringMvc’s controller a singleton mode? If so, what are the problems and how to solve them?

A: It is a singleton mode, so there is a thread safety problem during multithreaded access. Do not use synchronization, which will affect performance. The solution is that you cannot write fields in the controller.

11. What are the common annotations of Spring MVC?

@RequestMapping: annotation for processing request url mapping, which can be used on classes or methods. If it is used on a class, it means that all methods in the class that respond to requests take this address as the parent path.
@RequestBody: annotation implements receiving the json data of http requests and converting json into java objects.
@ResponseBody: the annotation implementation converts the returned object of the coneoller method into a json object to respond to the customer.

12. The controller annotation in SpringMvc usually uses that annotation. Is there any other annotation that can replace it?

Answer: The @ Controller annotation is generally used, and the @ RestController annotation can also be used. The @ RestController annotation is equivalent to @ ResponseBody ＋ @ Controller, representing the presentation layer. In addition, no other annotation is generally used instead.

13. If I want to intercept the get submission method in intercepting requests, how do I configure it?

A: You can add method=RequestMethod GET.

14. How to get the Request or Session in the method?

Answer: Declare the request directly in the formal parameter of the method, and SpringMvc will automatically pass in the request object.

15. If you want to get the parameters passed in from the foreground in the intercepting method, how can you get them?

Answer: It is OK to declare this parameter directly in the formal parameter, but the name must be the same as the passed parameter.

16. If there are many parameters passed in from the foreground, and these parameters are all the same object, how to get the object quickly?

Answer: Declare the object directly in the method, and SpringMvc will automatically assign the attribute to the object.

17. What is the return value of the function in SpringMvc?

Answer: The return value can have many types, including String and ModelAndView. The ModelAndView class combines views and data together, but it is generally better to use String.

18. What objects does SpringMvc use to transfer data from the background to the foreground?

Answer: Through the ModelMap object, you can call the put method in this object, add the object to it, and the foreground can get it through the el expression.

19. How to put the data in ModelMap into Session?

A: You can add @ SessionAttributes annotation to the class. The string contained in the annotation is the key to be put into the session.

20. How does the interceptor write in SpringMvc:

There are two writing methods, one is to implement the HandlerInterceptor interface, the other is to inherit the adapter class, and then implement the processing logic in the interface method; Then configure the interceptor in the configuration file of SpringMvc:

21. Annotation principle:

Annotation is a special interface that inherits Annotation in essence, and its specific implementation class is a dynamic proxy class generated by Java runtime. When we obtain annotations through reflection, we return the dynamic proxy object generated by the Java runtime. Calling a custom annotation method through a proxy object will eventually call the invoke method of AnnotationInvocationHandler. This method will retrieve the corresponding value from the memberValues map. The source of memberValues is the Java constant pool.