[学习交流] Filter-过滤器的使用详解

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Java过滤器-Filter过滤器的使用
过滤是SERVLET2。3规范新有的功能，目前TOMCAT4，WEBLOGIC7都已支持。它能实现很多以前使用不便或很难实现的功能，在产品体系中，我们可以很好地使用SERVLET过滤，使得各个部件可以在保持系统统一权限控制的前提下，来实现各个独自的个性权限系统。
一、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
{
}
}

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二、检测用户是否登陆的过滤器
1.写个过滤器

mport javax.servlet.Filter;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.FilterChain;
import java.io.IOException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpServletResponse;
public class RightFilter
implements Filter {
public void init(FilterConfig filterConfig) throws ServletException {
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse res = (HttpServletResponse) response;
HttpSession session = req.getSession(true);
//从session里取的用户名信息
String username = (String) session.getAttribute("username");
//判断如果没有取到用户信息,就跳转到登陆页面
if (username == null || "".equals(username)) {
//跳转到登陆页面
res.sendRedirect("http://"+req.getHeader("Host")+"/login.jsp");
}
else {
//已经登陆,继续此次请求
chain.doFilter(request,response);
}
}
public void destroy() {
}
}

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2.然后在web.xml里配置需要登陆权限验证的JSP文件:
a.如果是某个具体的JSP文件(如a.jsp)需要登陆验证
<web-app>
<filter>
<filter-name>right</filter-name>
<filter-class>com.taihuatalk.taihua.common.RightFilter</filter-class>
  </filter>
  <filter-mapping>
<filter-name>right</filter-name>
<url-pattern>/a.jsp</url-pattern>
  </filter-mapping>
</web-app>
b.如果是某一个目录(如a/目录)整个目录下的文件都需要登陆验证:
<web-app>
  <filter>
<filter-name>right</filter-name>
<filter-class>com.taihuatalk.taihua.common.RightFilter</filter-class>
  </filter>
<filter-mapping>
<filter-name>right</filter-name>
<url-pattern>/a/*</url-pattern>
  </filter-mapping>
</web-app>
三、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");
}
}

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2、在web.xml中做一些设置
<filter>
   <filter-name>code</filter-name>
   <filter-class>CharacterEncodingFilter</filter-class>
<init-param>
   <param-name>encoding</param-name>
   <param-value>GBK</param-value>
</init-param>
</filter>
  <filter-mapping>
   <filter-name>code</filter-name>
   <url-pattern>/*</url-pattern>
</filter-mapping>

servlet过滤器的执行顺序就是servlet过滤器在web.xml里面映射文件filter-mapping的顺序

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[学习交流] Filter-过滤器的使用详解

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