Filter Basics 2 (48)

Filter Chain Filterchain

When there are multiple connectors in a Web project, these filters filter the same URL. This is the formation of the filter chain/.

In the configuration of the filter, there are two configurations: filter,filter-mapping.

Filter-mapping before, then executes first, then executes after.

<filter>

<filter-name>first</filter-name>

<filter-class>cn.itcast.filter.FirstFilter</filter-class>

</filter>

<filter>

<filter-name>second</filter-name>

<filter-class>cn.itcast.filter.SecondFilter</filter-class>

</filter>

<filter-mapping>

<filter-name>second</filter-name>

<url-pattern>/four</url-pattern>

</filter-mapping>

<filter-mapping>

<filter-name>first</filter-name>

<url-pattern>/four</url-pattern>

</filter-mapping>

Filter Application 1-Set the request encoding

Write a filter that filters all URLs,/*. In the Dofilter method, set the code for request to Utf-8.

In general, this filter is always the first filter to be executed.

It is best to encode by configuration settings. <filter><init-param>, .....

The first step: Implement the filter interface, receive initialization parameters in Dofilter, set the encoding

Package cn.hongxin.filter;

import java.io.IOException;

import Javax.servlet.Filter;

import Javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

Public class Charfilter implements Filter {

Declaring the encoded member variable

Private String encoding;

Public void init (filterconfig config) throws servletexception {

encoding = Config.getinitparameter ("BM");

}

Public void DoFilter (servletrequest request, servletresponse response,

Filterchain chain) throws IOException, servletexception {

request.setcharacterencoding (encoding);

Release, must be released.

Chain.dofilter (request, response);

}

Public void Destroy () {

}

}

Step Two: Configure the above class to Web. xml

<filter>

<filter-name>char</filter-name>

<filter-class>cn.itcast.filter.CharFilter</filter-class>

<init-param>

<!--set the encoding in the configuration file for ease of configuration--

<param-name>BM</param-name>

<param-value>UTF-8</param-value>

</init-param>

</filter>

<filter-mapping>

<filter-name>char</filter-name>

<url-pattern>/*</url-pattern>

</filter-mapping>

For get can handle Chinese

The reuqest is packaged in the Charfilter.

Purpose: Modify the enhanced GetParameter method, if it is a get transcoding.

First step: Declare the wrapper class:

Declaring wrapper classes

class Myrequest extends httpservletrequestwrapper{

Public Myrequest (HttpServletRequest request) {

Super (request);

}

Enhanced Getparamter

@Override

Public String GetParameter (string name) {

String val = Super. GetParameter (name);

if (Super. GetMethod (). Equals ("GET")) {

Try {

val = new String (val.getbytes ("Iso-8859-1"),Super. getcharacterencoding ());

} catch (Unsupportedencodingexception e) {

E.printstacktrace ();

}

}

return Val;

}

}

Step two: In the Dofilter method, declare an instance of the wrapper class

Package cn.hongxin.filter;

import java.io.IOException;

import java.io.UnsupportedEncodingException;

import Javax.servlet.Filter;

import Javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServletRequest;

import Javax.servlet.http.HttpServletRequestWrapper;

Public class Charfilter implements Filter {

Declaring the encoded member variable

Private String encoding;

Public void init (filterconfig config) throws servletexception {

encoding = Config.getinitparameter ("BM");

}

Public void DoFilter (servletrequest request, servletresponse response,

Filterchain chain) throws IOException, servletexception {

request.setcharacterencoding (encoding);

Response.setcontenttype ("text/html;charset=" + encoding);

Determine if packaging is required

HttpServletRequest req = (httpservletrequest) request;

if (Req.getmethod (). Equals ("GET")) {

Request = New myrequest (req);

}

Declaring an instance of a wrapper class

Release

Chain.dofilter (request, response);

}

Public void Destroy () {

}

}

Declaring wrapper classes

class Myrequest extends httpservletrequestwrapper {

Public Myrequest (HttpServletRequest request) {

Super (request);

}

Enhanced Getparamter

@Override

Public String GetParameter (string name) {

String val = Super. GetParameter (name);

Try {

val = new String (val.getbytes ("iso-8859-1"),

Super. getcharacterencoding ());

} catch (Unsupportedencodingexception e) {

E.printstacktrace ();

}

return Val;

}

}

Filter Basics 2 (48)