java中filter的用法

filter過濾器主要使用於前臺向後臺傳遞資料是的過濾操作。程度很簡單就不說明了，直接給幾個已經寫好的程式碼：

一、使瀏覽器不快取頁面的過濾器

Java程式碼

import javax.servlet.*;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

/**
* 用於的使 Browser 不快取頁面的過濾器
*/
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、檢測使用者是否登陸的過濾器

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;
/**
* 用於檢測使用者是否登陸的過濾器，如果未登入，則重定向到指的登入頁面
* 配置引數
* checkSessionKey 需檢查的在 Session 中儲存的關鍵字
* redirectURL 如果使用者未登入，則重定向到指定的頁面，URL不包括 ContextPath
* notCheckURLList 不做檢查的URL列表，以分號分開，並且 URL 中不包括 ContextPath
*/
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、字元編碼的過濾器

import javax.servlet.*;
import java.io.IOException;
/**
* 用於設定 HTTP 請求字元編碼的過濾器，通過過濾器引數encoding指明使用何種字元編碼,用於處理Html Form請求引數的中文問題
*/
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、記錄使用者的訪問操作器

程式碼：
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 {
        //記錄使用者的訪問操作
        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);
            }

            //儲存到資料庫中
            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){
            //將報表任務資料儲存到資料庫中
            Connection conn = null;
            Statement st = null;

try {

                //構造sql表示式，將資料插入資料庫
                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防止使用者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方法的第一個引數為ServletRequest物件。此物件給過濾器提供了對進入的資訊（包括表單資料、cookie和HTTP請求頭）的完全訪問。第二個引數為ServletResponse，通常在簡單的過濾器中忽略此引數。最後一個引數為FilterChain，此引數用來呼叫servlet或JSP頁。
HttpServletRequest request = (HttpServletRequest)servletRequest;//;//如果處理HTTP請求，並且需要訪問諸如getHeader或getCookies等在ServletRequest中無法得到的方法，就要把此request物件構造成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()); //擷取到當前檔名用於比較
HttpSession session = request.getSession(false);
if (!"/login.jsp".equals(targetURL)) {//判斷當前頁是否是重定向以後的登入頁面頁面，如果是就不做session的判斷，防止出現死迴圈
if (session == null || session.getAttribute("user") == null) {//*使用者登入以後需手動新增session
System.out.println("request.getContextPath()=" + request.getContextPath());
response.sendRedirect(request.getContextPath() + "/login.jsp");//如果session為空表示使用者沒有登入就重定向到login.jsp頁面
return;
}
}
//加入filter鏈繼續向下執行
filterChain.doFilter(request, response);//.呼叫FilterChain物件的doFilter方法。Filter介面的doFilter方法取一個FilterChain物件作為它的一個引數。在呼叫此物件的doFilter方法時，啟用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頁面被啟用。
}
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>//表示對所有jsp檔案有效
</filter-mapping>

java中filter的用法

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