本文研究的主要是java中filter过滤器的相关用法，具体实现代码如下。
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
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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
{
}
}
二、检测用户是否登陆的过滤器
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;
/**
* 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");
}
}
四、记录用户的访问操作器
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 {
}
}
html
<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>
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