Spring MVC advanced - how to use interceptors correctly? Case explanation

Keywords: Java Spring JSP

;

Spring MVC: interceptor

Implemented the HandlerInterceptor interface.

Function: used to intercept the controller

 

2, Define an interceptor

1. Environment construction

@Component
public class Demo1Interceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        return false;
    }
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {

    }
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {

    }
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2. Register interceptor

@Configuration
@ComponentScan(basePackages={"com.czxy"})
@EnableWebMvc
public class MVCConfiguration extends WebMvcConfigurerAdapter{

    /**
     * view resolver
     * @return
     */
    @Bean
    public InternalResourceViewResolver getInternalResourceViewResolver(){
        InternalResourceViewResolver internalResourceViewResolver = new InternalResourceViewResolver();
        internalResourceViewResolver.setPrefix("/");
        internalResourceViewResolver.setSuffix(".jsp");
        return internalResourceViewResolver;
    }

    /*
    * Register interceptor
    * */
    //1. Define a member variable to get the interceptor object (variable name = class name small hump)
    @Resource
    private HandlerInterceptor demo1Interceptor;
    //2. Override register interceptor method, register interceptor
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        //Add interceptor (register interceptor)
        InterceptorRegistration i1 = registry.addInterceptor(demo1Interceptor);
        //Set the interception path of the interceptor
        i1.addPathPatterns("/**");
    }
}

 

3. Code implementation

Demo1Interceptor:

@Component
public class Demo1Interceptor implements HandlerInterceptor {
    /*
    * Pretreatment method:
    *       Execute before executing a controller
    *       true:Execution controller method (release)
    *       false: Intercept, do not execute controller method (do not release, intercept)
    * */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("demo1Interceptor-Pretreatment method");
        return true;
    }
    /*
    * Post processing method:
    *       After a controller method is executed
    *       ModelAndView: Used to modify the jump path of the controller
    * */
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("demo1Interceptor-Post processing method");
    }
    /*
    * Completion method:
    *       After all functions are executed, the method is executed finally
    * */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("demo1Interceptor-Completion method");
    }
}

 

 

4. Precautions: three methods of interceptors

  • preHandle: preprocessing method

Before the controller is executed.

Special: control whether the controller executes through the return value.

true: release, executed by controller

false: do not release or intercept, controller does not execute

Applicable environment: suitable for judgment before executing the controller.

 

  • postHandle: post processing method

Precondition: 1. Preprocessing method, return value true

2. The controller is normal

Execute after controller execution.

Applicable environment: applicable to modifying jump path / jump mode after executing controller

 

@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
    modelAndView.setViewName("errorMsg");
    System.out.println("demo1Interceptor-Post processing method");
}

 

  • afterCompletion: method after completion

Precondition: preprocessing method, return value true

After all processes are executed, they must be executed anyway, which is equivalent to finally

Applicable environment: if no exception handler is set, the method can handle exceptions after completion

 

/*
* Method after completion:
*       After all functions are executed, the method is executed finally
* */
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
    System.out.println("The exception of the controller is:"+ex);
    System.out.println("demo1Interceptor-Completion method");
}

 

 

5. Precautions: execution sequence diagram

 

 

 

6. Precautions: difference between filter and interceptor

 

 

  • filter:

① Implemented the Filter interface

② It is used to intercept requests to the server, or request forwarding, including, and errors within the server

③ The filter executes before the servlet

④ Filters are web components that block all web resources

 

  • Interceptor:

① Implemented the HandlerInterceptor interface

② It is only used to intercept requests to the controller, or to jump the request forwarding of the controller within the server

③ The interceptor executes after the servlet and before the controller

④ Interceptor is the spring MVC component, which is responsible for intercepting the controller

 

 

 

3, Define multiple interceptors

1. Code implementation

Demo2Interceptor:

@Component
public class Demo2Interceptor implements HandlerInterceptor {
    /*
    * Pretreatment method:
    *       Execute before executing a controller
    *       true:Execution controller method (release)
    *       false: Intercept, do not execute controller method (do not release, intercept)
    * */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("demo2Interceptor-Pretreatment method");
        return true;
    }
    /*
    * Post processing method:
    *       After a controller method is executed
    *       ModelAndView: Used to modify the jump path of the controller.
    * */
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
//        modelAndView.setViewName("errorMsg");
        System.out.println("demo2Interceptor-Post processing method");
    }
    /*
    * Method after completion:
    *       After all functions are executed, the method is executed finally
    * */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
//         System.out.println("exception of controller:" + ex);
        System.out.println("demo2Interceptor-Completion method");
    }
}

 

MVC configuration class:

@Configuration
@ComponentScan(basePackages={"com.czxy"})
@EnableWebMvc
public class MVCConfiguration extends WebMvcConfigurerAdapter{

    /**
     * view resolver
     * @return
     */
    @Bean
    public InternalResourceViewResolver getInternalResourceViewResolver(){
        InternalResourceViewResolver internalResourceViewResolver = new InternalResourceViewResolver();
        internalResourceViewResolver.setPrefix("/");
        internalResourceViewResolver.setSuffix(".jsp");
        return internalResourceViewResolver;
    }

    /*
    * Register interceptor
    * */
    //1. Define a member variable to get the interceptor object (variable name = class name small hump)
    @Resource
    private HandlerInterceptor demo1Interceptor;
    @Resource
    private HandlerInterceptor demo2Interceptor;
    //2. Override register interceptor method, register interceptor
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        //Add interceptor (register interceptor)
        InterceptorRegistration i1 = registry.addInterceptor(demo1Interceptor);
        //Set the interception path of the interceptor
        i1.addPathPatterns("/**");

        //Add interceptor (register interceptor)
        InterceptorRegistration i2 = registry.addInterceptor(demo2Interceptor);
        //Set the interception path of the interceptor
        i2.addPathPatterns("/**");
    }
}

 

 

2. Flow chart

The first to register, the first to implement.

 

 

 

 

IV. springMVC advanced interceptor wildcard settings

 

wildcard

explain

**

Any 0 ~ characters or any multi-level directory

For example, / user/**

/user/a/b/c/run1.action

/user/run1.action

 

*

Any 0 to more than one character

For example, / user/*

/user/run1.action

/user/run2.action

 

 

?

Any character

For example, / user/**

/userA/run1.action

/userb/run1.action

/userc/run1.action

 

 

Summary:

Interceptor: implements the HandlerInterceptor interface.

Interceptor: intercepts only controllers.

 

  • Pretreatment method:

Execute before the controller executes.

True: release.

False: intercept.

 

  • Post processing method:

After normal execution of the controller.

Premise: ① preprocessing method returns true

② The controller cannot throw an exception

 

  • Method after completion:

After the end of the process.

Premise: preprocessing method returns true


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Posted by emma57573 on Wed, 20 May 2020 23:03:42 -0700