Servlet Filter--filter

First, the definition:

• is a special servlet, can be used to filter the request, multiple filters can form a filter chain;
• The request can be intercepted and processed with a filter before the request is sent to the servlet, and the response can be processed with a filter after the servlet has finished working and before the response is sent back to the customer.
• Implementation of the Javax.servlet.Filter interface inside the Init,dofilter, destroy and other abstract methods, is the life cycle of the filter.

• How the Filter works:

ii. configuration declarations in Web. XML

• According to the servlet2.3 specification, filter execution is carried out in accordance with filter-mapping order;
• The first code: declaring the filter name; the second code: mapping filters to filter mappings for the Web resource declaration corresponding URL pattern you want to filter

<filter>               <filter-name>  file name </filter-name>               <filter-class> package name. File name </ Filter-class>               <init-param>{  optional}                     <param-name> variable name  </param-name >                      <param-value>  variables </param-value>                 </init-param>      </filter>

<filter-mapping>     <filter-name> file name </filter-name>     <url-pattern> /* </url-pattern></filter-mapping>

• If you are connected to a servlet, insert the following code:

<servlet>      <servlet-name>Demo1</servlet-name>      <servlet-class>servlet. Demo1</servlet-class> </servlet>

Iii. Examples of contact with servlets-solving Chinese problems1. Create a new Javaweb project TESTFL, create a characterencoderfilter.java--under the filter package

 Public classCharacterencoderfilterImplementsfilter{PrivateFilterconfig filterconfig=NULL;  Public voiddestroy () {} Public voidDoFilter (servletrequest req, Servletresponse resp, filterchain chain)throwsIOException, servletexception {String charset=filterconfig.getinitparameter ("CharSet");           Req.setcharacterencoding (CharSet);           Resp.setcharacterencoding (CharSet); Resp.setcontenttype ("Text/html;charset=" +charset);     Chain.dofilter (req, resp); }   Public voidInit (Filterconfig filterconfig)throwsservletexception { This. filterconfig=Filterconfig; } } 

2, demo2.java--under the servlet package

 Public classDemo2extendsHttpServlet { Public voiddoget (httpservletrequest request, httpservletresponse response)throwsservletexception, IOException {doPost (request, response); }  Public voidDoPost (httpservletrequest request, httpservletresponse response)throwsservletexception, IOException {String username=request.getparameter ("username");          SYSTEM.OUT.PRINTLN (username); Response.getwriter (). Write (Chinese); }}

3. In Web. XML, the filter file name, variable name, and servlet file are declared again:

(Note that the/* is the URL does not need to write the file name, just write http://localhost:8080/TestFL/,

if/abc/*, write as http://localhost:8080/TestFL/abc/to run)

 <filter> <filter-name>CharacterEncoderFilter</filter-name> <filter-class>filter.          Characterencoderfilter</filter-class> <init-param> <param-name>charset</param-name>        <param-value>utf-8</param-value> </init-param> </filter><filter-mapping> <filter-name>CharacterEncoderFilter</filter-name> <url-pattern>  /*  </url-pattern></filter-mapping><servlet> < Servlet-name>demo1</servlet-name> <servlet-class>servlet. Demo1</servlet-class></servlet> <servlet-mapping> <servlet-name>demo1</servlet-name > <url-pattern>/Demo1</url-pattern></servlet-mapping>  

3, design a simple form in the JSP file:(remember to change the pageencoding to Utf-8)

<formAction= "/testfl/demo2"Method= "POST">User name:<inputname= "username"/>         <inputtype= "Submit"value= "Submit" /> </form>

4, open the Tomcat service, redeploy deployment files, run http://localhost:8080/TestFL/on the browser, after submission: (All page requests are filtered through the filter)

Servlet Filter--filter