filter过滤器主要使用于前台向后台传递数据是的过滤操作。程度很简单就不说明了，直接给几个已经写好的代码：
一、使浏览器不缓存页面的过滤器
Java代码 复制代码
import javax.servlet.*;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
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
{
}
}
二、检测用户是否登陆的过滤器
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.util.List;
import java.util.ArrayList;
import java.util.StringTokenizer;
import java.io.IOException;
public class CheckLoginFilter
implements Filter
{
protected FilterConfig
filterConfig = null;
private String
redirectURL = null;
private List
notCheckURLList = new ArrayList();
private String
sessionKey = null;
public void doFilter(ServletRequest
servletRequest, ServletResponse servletResponse, FilterChain
filterChain) throws IOException, ServletException
{
HttpServletRequest request =
(HttpServletRequest) servletRequest;
HttpServletResponse response =
(HttpServletResponse) servletResponse;
HttpSession session =
request.getSession();
if(sessionKey == null)
{
filterChain.doFilter(request, response);
return;
}
if((!checkRequestURIIntNotFilterList(request)) &&
session.getAttribute(sessionKey) == null)
{
response.sendRedirect(request.getContextPath() +
redirectURL);
return;
}
filterChain.doFilter(servletRequest,
servletResponse);
}
public void destroy()
{
notCheckURLList.clear();
}
private boolean
checkRequestURIIntNotFilterList(HttpServletRequest request)
{
String uri = request.getServletPath() +
(request.getPathInfo() == null ? "" : request.getPathInfo());
return notCheckURLList.contains(uri);
}
public void init(FilterConfig filterConfig)
throws ServletException
{
this.filterConfig = filterConfig;
redirectURL =
filterConfig.getInitParameter("redirectURL");
sessionKey =
filterConfig.getInitParameter("checkSessionKey");
String notCheckURLListStr =
filterConfig.getInitParameter("notCheckURLList");
if(notCheckURLListStr != null)
{
StringTokenizer st = new
StringTokenizer(notCheckURLListStr, ";");
notCheckURLList.clear();
while(st.hasMoreTokens())
{
notCheckURLList.add(st.nextToken());
}
}
}
}
三、字符编码的过滤器
import javax.servlet.*;
import java.io.IOException;
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");
}
}
四、记录用户的访问操作器
代码：
package com.qwserv.itm.pfl.log.svr;
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 java.text.SimpleDateFormat;
import javax.servlet.http.HttpServletRequest;
import com.qwserv.itm.api.pfl.sm.vo.Person;
import java.sql.*;
import com.qwserv.itm.api.ServiceAccess;
import com.qwserv.itm.util.toolkit.DebugUtil;
public class ObserveFilter implements Filter {
protected static
DebugUtil log = DebugUtil.getInstances("pfl-log",
ObserveFilter.class);
public void destroy()
{
}
public void
doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException,
ServletException {
//记录用户的访问操作
HttpServletRequest request1 =
(HttpServletRequest)request;
StringBuffer url =
request1.getRequestURL();
//对url进行过滤，如果是js/css/image则不进行处理
if (judgeFile(url.toString())){
String
operTime = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").
format(new
java.util.Date());
String
hostIp = request.getRemoteAddr();
String
sessionId = request1.getRequestedSessionId();
String
userId = "";
Person
person =
(Person)request1.getSession().getAttribute("userObj");
if (null
!= person && null != person.getUser()){
userId =
person.getUser().getId();
}
String
queryString = request1.getQueryString();
if (null
!= queryString) {
url.append('?');
url.append(queryString);
}
//保存到数据库中
saveToDb(userId,hostIp,sessionId,url.toString(),operTime,"");
}
// Pass control on to the next filter
chain.doFilter(request, response);
}
public void
init(FilterConfig filterConfig) throws ServletException {
}
public boolean
judgeFile(String url){
if (url.endsWith(".gif") || url.endsWith(".jpg")
|| url.endsWith(".png")
||
url.endsWith(".bmp") || url.endsWith(".css") ||
url.endsWith(".js")
||
url.endsWith(".jsx")){
return
false;
} else {
return
true;
}
}
public int
saveToDb(String userId, String hostIp,String sessionId,String
url,
String operTime,String desc){
//将报表任务数据保存到数据库中
Connection
conn = null;
Statement
st = null;
try
{
//构造sql表达式，将数据插入数据库
conn =
ServiceAccess.getSystemSupportService().getDefaultConnection();
st =
conn.createStatement();
String sql = "insert into
LOG_OBSERVE_HISTORY(USERID,URL,Detail,SessionID,HostName,StartDate)
values('"+
userId +
"','" + url + "','" + desc + "','" + sessionId
+ "','" +
hostIp + "','" + operTime + "')";
if
(ServiceAccess.getSystemSupportService().getConnectionType(conn)==ServiceAccess.getSystemSupportService().JCA_TYPE_ORACLE){
sql = "insert into
LOG_OBSERVE_HISTORY(Id,USERID,URL,Detail,SessionID,HostName,StartDate)
values(LOG_OBSERVE_SEQ.nextval,'"+
userId +
"','" + url + "','" + desc + "','" + sessionId
+ "','" +
hostIp + "',TO_DATE('" + operTime
+
"','YYYY-MM-DD HH24:MI:SS'))";
}
st.executeUpdate(sql);
} catch
(Exception e) {
e.printStackTrace();
log.error("--------------------The url String is:" + url +
"-------------------------------");
return 1;
//表示操作失败
} finally
{
if (null != st)
{
try{
st.close();
}
catch(Exception e)
{
e.printStackTrace();
}
st = null;
}
if (conn != null) {
try {
conn.close();
} catch (Exception e) {
e.printStackTrace();
}
conn = null;
}
}
return 0;
//表示操作成功
}
}
≤filter≥
≤filter-name≥ObserveFilter≤/filter-name≥
≤filter-class≥com.qwserv.itm.pfl.log.svr.ObserveFilter≤/filter-class≥
≤/filter≥
≤filter-mapping≥
≤filter-name≥ObserveFilter≤/filter-name≥
≤url-pattern≥/*≤/url-pattern≥
≤/filter-mapping≥
五.Filter防止用户访问一些未被授权的资源
package
com.drp.util.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;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class AuthFilter implements Filter {
public void destroy() {
}
public void doFilter(ServletRequest
servletRequest, ServletResponse servletResponse,
FilterChain filterChain)
throws IOException, ServletException
{//1,doFilter方法的第一个参数为ServletRequest对象。此对象给过滤器提供了对进入的信息（包括表单数据、cookie和HTTP请求头）的完全访问。第二个参数为ServletResponse，通常在简单的过滤器中忽略此参数。最后一个参数为FilterChain，此参数用来调用servlet或JSP页。
HttpServletRequest request =
(HttpServletRequest)servletRequest;//;//如果处理HTTP请求，并且需要访问诸如getHeader或getCookies等在ServletRequest中无法得到的方法，就要把此request对象构造成HttpServletRequest
HttpServletResponse response =
(HttpServletResponse)servletResponse。
String currentURL =
request.getRequestURI();//取得根目录所对应的绝对路径:
String targetURL =
currentURL.substring(currentURL.indexOf("/", 1),
currentURL.length()); //截取到当前文件名用于比较
HttpSession session =
request.getSession(false);
if (!"/login.jsp".equals(targetURL))
{//判断当前页是否是重定向以后的登录页面页面，如果是就不做session的判断，防止出现死循环
if (session == null ||
session.getAttribute("user") == null) {//*用户登录以后需手动添加session
System.out.println("request.getContextPath()=" +
request.getContextPath());
response.sendRedirect(request.getContextPath() +
"/login.jsp");//如果session为空表示用户没有登录就重定向到login.jsp页面
return;
}
}
//加入filter链继续向下执行
filterChain.doFilter(request,
response);//.调用FilterChain对象的doFilter方法。Filter接口的doFilter方法取一个FilterChain对象作为它的一个参数。在调用此对象的doFilter方法时，激活下一个相关的过滤器。如果没有另一个过滤器与servlet或JSP页面关联，则servlet或JSP页面被激活。
}
public void init(FilterConfig filterConfig)
throws ServletException {
}
}
≤filter≥
≤filter-name≥AuthFilter≤/filter-name≥
≤filter-class≥com.drp.util.filter.AuthFilter≤/filter-class≥
≤/filter≥
≤filter-mapping≥
≤filter-name≥AuthFilter≤/filter-name≥
≤url-pattern≥*.jsp≤/url-pattern≥//表示对所有jsp文件有效
≤/filter-mapping≥