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本文研究的主要是Java中filter過濾器的相關用法，具體實現代碼如下。
filter過濾器主要使用于前臺向后臺傳遞數據是的過濾操作。程度很簡單就不說明了，直接給幾個已經寫好的代碼：
一、使瀏覽器不緩存頁面的過濾器
import javax.servlet.*;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
/**
* 用于的使 Browser 不緩存頁面的過濾器
*/
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、檢測用戶是否登陸的過濾器
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、字符編碼的過濾器
import javax.servlet.*;
import java.io.IOException;
/**
* 用于設置 HTTP 請求字符編碼的過濾器，通過過濾器參數encoding指明使用何種字符編碼,用于處理Html Form請求參數的中文問題
*/
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、記錄用戶的訪問操作器
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 {
//記錄用戶的訪問操作
HttpServletRequest request1 = (HttpServletRequest)request;
StringBuffer url = request1.getRequestURL();
//對url進行過濾，如果是js/css/image則不進行處理
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);
}
//保存到數據庫中
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){
//將報表任務數據保存到數據庫中
Connection conn = null;
Statement st = null;
try {
//構造sql表達式，將數據插入數據庫
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;
//表示操作失敗
}
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防止用戶訪問一些未被授權的資源
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方法的第一個參數為ServletRequest對象。此對象給過濾器提供了對進入的信息（包括表單數據、cookie和HTTP請求頭）的完全訪問。第二個參數為ServletResponse，通常在簡單的過濾器中忽略此參數。最后一個參數為FilterChain，此參數用來調用servlet或JSP頁。
HttpServletRequest request = (HttpServletRequest)servletRequest;
//;//如果處理HTTP請求，并且需要訪問諸如getHeader或getCookies等在ServletRequest中無法得到的方法，就要把此request對象構造成HttpServletRequest
HttpServletResponse response = (HttpServletResponse)servletResponse。
String currentURL = request.getRequestURI();
//取得根目錄所對應的絕對路徑:
String targetURL = currentURL.substring(currentURL.indexOf("/", 1), currentURL.length());
//截取到當前文件名用于比較
HttpSession session = request.getSession(false);
if (!"/login.jsp".equals(targetURL)) {
//判斷當前頁是否是重定向以后的登錄頁面頁面，如果是就不做session的判斷，防止出現死循環
if (session == null || session.getAttribute("user") == null) {
//*用戶登錄以后需手動添加session
System.out.println("request.getContextPath()=" + request.getContextPath());
response.sendRedirect(request.getContextPath() + "/login.jsp");
//如果session為空表示用戶沒有登錄就重定向到login.jsp頁面
return;
}
}
//加入filter鏈繼續向下執行
filterChain.doFilter(request, response);
//.調用FilterChain對象的doFilter方法。Filter接口的doFilter方法取一個FilterChain對象作為它的一個參數。在調用此對象的doFilter方法時，激活下一個相關的過濾器。如果沒有另一個過濾器與servlet或JSP頁面關聯，則servlet或JSP頁面被激活。
}
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>//表示對所有jsp文件有效 </filter-mapping>
總結
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