Catalog

One 、Servlet

Two 、Filter

1. Concept

2. step

3. Code

4. Filter details

4.1web.xml To configure

4.2 Filter execution process

4.3 Filter configuration details

5. Filter chain

3、 ... and 、Listener 

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One 、Servlet

  Click here to introduce the past servlet

Two 、Filter

1. Concept

* Filters in life ： Water purifier , air cleaner , bandit 、
* web Filter in ： When accessing the server's resources , Filters can intercept requests , Complete some special functions .
* The function of the filter ：
     * Generally used to complete general operations . Such as ： validate logon 、 Unified coding 、 Sensitive character filtering ...

2. step

1. Define a class , Implementation interface Filter
     2. Replication method
     3. Configure interception path
          1. web.xml
          2. annotation

3. Code

@WebFilter("/*")// Before accessing all resources , Will execute the filter
     public class FilterDemo1 implements Filter {
        @Override
             public void init(FilterConfig filterConfig) throws ServletException {
        
             }
        
            @Override
            public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
                System.out.println("filterDemo1 Carried out ....");
               // release
                filterChain.doFilter(servletRequest,servletResponse);
        
            }
        
            @Override
            public void destroy() {
        
            }
        }

4. Filter details

4.1web.xml To configure

<filter>
            <filter-name>demo1</filter-name>
            <filter-class>cn.itcast.web.filter.FilterDemo1</filter-class>
        </filter>
        <filter-mapping>
            <filter-name>demo1</filter-name>
            <!-- Intercept path -->
            <url-pattern>/*</url-pattern>
        </filter-mapping>

4.2 Filter execution process

1. Perform filter
2. Resources after implementation of release
3. Come back and execute the code below the filter release code

4.3 Filter configuration details

* Intercept path configuration ：
            1. Specific resource paths ： /index.jsp   Only visit index.jsp Resource time , The filter will be executed
            2. Intercept Directory ： /user/*     visit /user All resources under , Filters are executed
            3. Suffix blocking ： *.jsp         Access all suffixes named jsp Resource time , Filters are executed
            4. Intercept all resources ：/*         When accessing all resources , Filters are executed
       * Interception mode configuration ： How resources are accessed
          * Annotation configuration ：
               * Set up dispatcherTypes attribute
                    1. REQUEST： The default value is . Browser requests resources directly
                    2. FORWARD： Forward access to resources
                    3. INCLUDE： Contains access to resources
                    4. ERROR： Wrong jump resource
                    5. ASYNC： Asynchronous access to resources
         * web.xml To configure
              * Set up <dispatcher></dispatcher> Labels can be

5. Filter chain

* Execution order ： If there are two filters ： filter 1 And filters 2
            1. filter 1
            2. filter 2
            3. Resource execution
            4. filter 2
            5. filter 1 

        * The filter sequence problem ：
            1. Annotation configuration ： Compare according to the string comparison rules of class names , If it's worth less, execute it first
                 * Such as ： AFilter and BFilter,AFilter Just do it first .
            2. web.xml To configure ： <filter-mapping> Who is defined above , Who will execute first

3、 ... and 、Listener 

* Concept ：web One of the three components of .
    * Event monitoring mechanism
        * event     ： One more thing
        * Event source ： Where it happened
        * Monitor ： An object
        * Register to listen ： Put the event 、 Event source 、 Listeners are bound together . When an event occurs on the event source , Execute listener code

* ServletContextListener: monitor ServletContext Object creation and destruction
     * Method ：
         * void contextDestroyed(ServletContextEvent sce) ：ServletContext The method is called before the object is destroyed
         * void contextInitialized(ServletContextEvent sce) ：ServletContext The method is called after the object is created
     * step ：
        1. Define a class , Realization ServletContextListener Interface
        2. Replication method
        3. To configure
           1. web.xml
                     <listener>
                     <listener-class>cn.itcast.web.listener.ContextLoaderListener</listener-class>
                             * Specify initialization parameters <context-param>
           2. annotation ：
                 * @WebListener