Servlet过滤器

一、字符编码的过滤器

import javax.servlet.*; 
import java.io.IOException; 

/** 
* 用于设置 HTTP 请求字符编码的过滤器，通过过滤器参数encoding指明使用何种字符编码,用于处理Html Form请求参数的中文问题 
*/ 
public class CharacterEncodingFilter 
implements Filter 
{ 
protected FilterConfig filterConfig = null; 
protected String encoding = ""; 

public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException 
{ 
if(encoding != null) 
servletRequest.setCharacterEncoding(encoding); 
filterChain.doFilter(servletRequest, servletResponse); 
} 

public void destroy() 
{ 
filterConfig = null; 
encoding = null; 
} 

public void init(FilterConfig filterConfig) throws ServletException 
{ 
this.filterConfig = filterConfig; 
this.encoding = filterConfig.getInitParameter("encoding"); 

} 
} 

要传递参数的时候最好使用form进行传参，如果使用链接的话当中文字符的时候过滤器转码是不会起作用的，还有就是页面上form的method也要设置为post，不然过滤器也起不了作用。


二、使浏览器不缓存页面的过滤器

import javax.servlet.*; 
import javax.servlet.http.HttpServletResponse; 
import java.io.IOException; 

/** 
* 用于的使 Browser 不缓存页面的过滤器 
*/ 
public class ForceNoCacheFilter implements Filter { 

public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException 
{ 
((HttpServletResponse) response).setHeader("Cache-Control","no-cache"); 
((HttpServletResponse) response).setHeader("Pragma","no-cache"); 
((HttpServletResponse) response).setDateHeader ("Expires", -1); 
filterChain.doFilter(request, response); 
} 

public void destroy() { 
} 

public void init(FilterConfig filterConfig) throws ServletException { 
} 
} 

三 利用Filter限制用户浏览权限

在一个系统中通常有多个权限的用户。不同权限用户的可以浏览不同的页面。使用Filter进行判断不仅省下了代码量，而且如果要更改的话只需要在Filter文件里动下就可以。
以下是Filter文件代码：

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; 
import javax.servlet.http.HttpServletRequest; 

public class RightFilter implements Filter { 

public void destroy() { 

} 

public void doFilter(ServletRequest sreq, ServletResponse sres, FilterChain arg2) throws IOException, ServletException { 
// 获取uri地址 
HttpServletRequest request=(HttpServletRequest)sreq; 
String uri = request.getRequestURI(); 
String ctx=request.getContextPath(); 
uri = uri.substring(ctx.length()); 
//判断admin级别网页的浏览权限 
if(uri.startsWith("/admin")) { 
if(request.getSession().getAttribute("admin")==null) { 
request.setAttribute("message","您没有这个权限"); 
request.getRequestDispatcher("/login.jsp").forward(sreq,sres); 
return; 
} 
} 
//判断manage级别网页的浏览权限 
if(uri.startsWith("/manage")) { 
//这里省去 
} 
} 
//下面还可以添加其他的用户权限，省去。 

} 

public void init(FilterConfig arg0) throws ServletException { 

} 

} 

<!-- 判断页面的访问权限 --> 
<filter> 
<filter-name>RightFilter</filter-name> 
<filter-class>cn.itkui.filter.RightFilter</filter-class> 
</filter> 
<filter-mapping> 
<filter-name>RightFilter</filter-name> 
<url-pattern>/admin/*</url-pattern> 
</filter-mapping> 
<filter-mapping> 
<filter-name>RightFilter</filter-name> 
<url-pattern>/manage/*</url-pattern> 
</filter-mapping> 

在web.xml中加入Filter的配置，如下： 
<filter> 

<filter-name>EncodingAndCacheflush</filter-name> 
<filter-class>EncodingAndCacheflush</filter-class> 
<init-param> 
<param-name>encoding</param-name> 
<param-value>UTF-8</param-value> 
</init-param> 
</filter> 
<filter-mapping> 
<filter-name>EncodingAndCacheflush</filter-name> 
<url-pattern>/*</url-pattern> 
</filter-mapping>