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The content of this article mainly focuses on the use of SpringMVC HandlerInterceptor interceptor and what are the parameters. The content of the article is clear and clear. It is very suitable for beginners to learn and is worth reading. Interested friends can follow the editor to read together. I hope you can get something through this article!

Interceptor concept:

Interceptor (Interceptor) is a mechanism for dynamically intercepting method calls, and the request processing process is parsed.

Core principle: AOP thought

Interceptor chain: multiple interceptors enhance the original called function in a certain order

Function:

Executes the predetermined code before and after the specified method call

Prevent the execution of the original method

Interceptor VS filter

Different attribution: filter belongs to Servlet technology, interceptor belongs to SpringMVC technology to intercept content is different: filter enhances all access, interceptor enhances access only for SpringMVC

Interceptor execution process:

Customize the interceptor development process:

Implement the HandlerInterceptor interface

/ / Custom interceptor needs to implement HandleInterceptor interface public class MyInterceptor implements HandlerInterceptor {/ / pre-processing method: execute @ Override public boolean preHandle (HttpServletRequest request, / / request object HttpServletResponse response, / / response object Object handler) / / called processor object before the original method, which is essentially a method object The Method object in reflection is repackaged, the method is encapsulated and enhanced, and the original object is manipulated, throws Exception {System.out.println ("pre-run") / / the return value of false will intercept the operation of the original processor, that is, whether to let it go. If the code behind false will not run, if it is true, continue to execute the following code / / if multiple interceptors are configured, the return value of false will terminate the running return true of the interceptor configured after the current interceptor } / / Post processing method: run after the original method is run. If the original method is intercepted, @ Override public void postHandle (HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) is not executed / / if the processor completes execution, the result is returned. You can read the corresponding data and page information to adjust throws Exception {System.out.println ("post run") } / / completion method: the last method executed by the interceptor, regardless of whether the original method executes @ Override public void afterCompletion (HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) / / if an exception object occurs during processor execution Throws Exception {System.out.println ("finish running") can be handled separately for exception cases. } / / the running order of the three methods is preHandle-> postHandle-> afterCompletion / / if the return value of preHandle is false, the three methods only run preHandle} interceptor configuration item: multi-interceptor configuration:

Running order: if it is configured first, it will be executed first.

Multi-interceptor execution order:

Responsibility chain model

The mode of responsibility chain is a kind of behavior mode.

Characteristics:

Execute sequentially along a predetermined chain of tasks, with each node having an independent task

Advantages:

Independence: only focus on the tasks of the current node, and let other tasks go directly to the next node

Isolation: with chain delivery characteristics, you don't need to know the overall link structure, you just need to wait for the request to arrive and process it.

Flexibility: the link structure can be arbitrarily modified to dynamically add or delete the overall link responsibility

Decoupling: decoupling dynamic tasks from original tasks

Disadvantages:

When the link is too long, the processing efficiency is low.

There may be circular references on the nodes, causing an endless loop and causing the system to crash.

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