java中filter的用法

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


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

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;

/**

* 用于检测用户是否登陆的过滤器，如果未登录，则重定向到指的登录页面<p>

* 配置参数<p>

* checkSessionKey 需检查的在 Session 中保存的关键字<br/>

* redirectURL 如果用户未登录，则重定向到指定的页面，URL不包括 ContextPath<br/>

* notCheckURLList 不做检查的URL列表，以分号分开，并且 URL 中不包括 ContextPath<br/>

*/

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

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>