引用 五個有用的過濾器 Filter

引用
xyz 的 五個有用的過濾器 Filter
來源：http://blogger.org.cn/blog
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;

/**
* 用於的使 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

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;

/**
* 用於檢測用戶是否登陸的過濾器，如果未登錄，則重定向到指的登錄頁面


* 配置參數


* checkSessionKey 需檢查的在 Session 中保存的關鍵字

* redirectURL 如果用戶未登錄，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、字符編碼的過濾器

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

/**
* 用於設置 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,用於處理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、資源保護過濾器


package catalog.view.util;

import javax.servlet.Filter;
import javax.servlet.FilterConfig;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
import java.util.Iterator;
import java.util.Set;
import java.util.HashSet;
//
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
* This Filter class handle the security of the application.
*
* It should be configured inside the web.xml.
*
* @author Derek Y. Shen
*/
public class SecurityFilter implements Filter {
//the login page uri
private static final String LOGIN_PAGE_URI = "login.jsf";

//the logger object
private Log logger = LogFactory.getLog(this.getClass());

//a set of restricted resources
private Set restrictedResources;

/**
* Initializes the Filter.
*/
public void init(FilterConfig filterConfig) throws ServletException {
this.restrictedResources = new HashSet();
this.restrictedResources.add("/createProduct.jsf");
this.restrictedResources.add("/editProduct.jsf");
this.restrictedResources.add("/productList.jsf");
}

/**
* Standard doFilter object.
*/
public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
throws IOException, ServletException {
this.logger.debug("doFilter");

String contextPath = ((HttpServletRequest)req).getContextPath();
String requestUri = ((HttpServletRequest)req).getRequestURI();

this.logger.debug("contextPath = " + contextPath);
this.logger.debug("requestUri = " + requestUri);

if (this.contains(requestUri, contextPath) && !this.authorize((HttpServletRequest)req)) {
this.logger.debug("authorization failed");
((HttpServletRequest)req).getRequestDispatcher(LOGIN_PAGE_URI).forward(req, res);
}
else {
this.logger.debug("authorization succeeded");
chain.doFilter(req, res);
}
}

public void destroy() {}

private boolean contains(String value, String contextPath) {
Iterator ite = this.restrictedResources.iterator();

while (ite.hasNext()) {
String restrictedResource = (String)ite.next();

if ((contextPath + restrictedResource).equalsIgnoreCase(value)) {
return true;
}
}

return false;
}

private boolean authorize(HttpServletRequest req) {

//處理用戶登錄
/* UserBean user = (UserBean)req.getSession().getAttribute(BeanNames.USER_BEAN);

if (user != null && user.getLoggedIn()) {
//user logged in
return true;
}
else {
return false;
}*/
}
}
五 利用Filter限制用戶瀏覽權限
在一個系統中通常有多個權限的用戶。不同權限用戶的可以瀏覽不同的頁面。使用Filter進行判斷不僅省下了代碼量，而且如果要更改的話只需要在Filter文件裏動下就可以。
以下是Filter文件代碼：
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;

public class RightFilter implements Filter {

public void destroy() {

}

public void doFilter(ServletRequest sreq, ServletResponse sres, FilterChain arg2) throws IOException, ServletException {
// 獲取uri地址
HttpServletRequest request=(HttpServletRequest)sreq;
String uri = request.getRequestURI();
String ctx=request.getContextPath();
uri = uri.substring(ctx.length());
//判斷admin級別網頁的瀏覽權限
if(uri.startsWith("/admin")) {
if(request.getSession().getAttribute("admin")==null) {
request.setAttribute("message","您沒有這個權限");
request.getRequestDispatcher("/login.jsp").forward(sreq,sres);
return;
}
}
//判斷manage級別網頁的瀏覽權限
if(uri.startsWith("/manage")) {
//這裏省去
}
}
//下面還可以添加其他的用戶權限，省去。

}

public void init(FilterConfig arg0) throws ServletException {

}

}
<!-- 判斷頁面的訪問權限 -->
<filter>
<filter-name>RightFilter</filter-name>
<filter-class>cn.itkui.filter.RightFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>RightFilter</filter-name>
<url-pattern>/admin/*</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>RightFilter</filter-name>
<url-pattern>/manage/*</url-pattern>
</filter-mapping>

在web.xml中加入Filter的配置，如下：
<filter>
<filter-name>EncodingAndCacheflush</filter-name>
<filter-class>EncodingAndCacheflush</filter-class>
<init-param>
<param-name>encoding</param-name>
<param-value>UTF-8</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>EncodingAndCacheflush</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
要傳遞參數的時候最好使用form進行傳參，如果使用鏈接的話當中文字符的時候過濾器轉碼是不會起作用的，還有就是頁面上
form的method也要設置爲post，不然過濾器也起不了作用。