javaweb學習總結(十六)——Filter(過濾器)常見應用
阿新 • • 發佈：2018-12-15
一、統一全站字元編碼
通過配置引數charset指明使用何種字元編碼,以處理Html Form請求引數的中文問題
package me.gacl.web.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.HttpServletRequestWrapper; import javax.servlet.http.HttpServletResponse; /** * @ClassName: CharacterEncodingFilter * @Description: 此過濾器用來解決全站中文亂碼問題 * @author: 孤傲蒼狼 * @date: 2014-8-31 下午11:09:37 * */ public class CharacterEncodingFilter implements Filter { private FilterConfig filterConfig = null; //設定預設的字元編碼 private String defaultCharset = "UTF-8"; public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) resp; String charset = filterConfig.getInitParameter("charset"); if(charset==null){ charset = defaultCharset; } request.setCharacterEncoding(charset); response.setCharacterEncoding(charset); response.setContentType("text/html;charset="+charset); MyCharacterEncodingRequest requestWrapper = new MyCharacterEncodingRequest(request); chain.doFilter(requestWrapper, response); } public void init(FilterConfig filterConfig) throws ServletException { //得到過濾器的初始化配置資訊 this.filterConfig = filterConfig; } public void destroy() { } } /* 1.實現與被增強物件相同的介面 2、定義一個變數記住被增強物件 3、定義一個構造器，接收被增強物件 4、覆蓋需要增強的方法 5、對於不想增強的方法，直接呼叫被增強物件（目標物件）的方法 */ class MyCharacterEncodingRequest extends HttpServletRequestWrapper{ private HttpServletRequest request; public MyCharacterEncodingRequest(HttpServletRequest request) { super(request); this.request = request; } /* 重寫getParameter方法 * @see javax.servlet.ServletRequestWrapper#getParameter(java.lang.String) */ @Override public String getParameter(String name) { try{ //獲取引數的值 String value= this.request.getParameter(name); if(value==null){ return null; } //如果不是以get方式提交資料的，就直接返回獲取到的值 if(!this.request.getMethod().equalsIgnoreCase("get")) { return value; }else{ //如果是以get方式提交資料的，就對獲取到的值進行轉碼處理 value = new String(value.getBytes("ISO8859-1"),this.request.getCharacterEncoding()); return value; } }catch (Exception e) { throw new RuntimeException(e); } } }
web.xml檔案中的配置如下：
<filter> <filter-name>CharacterEncodingFilter</filter-name> <filter-class>me.gacl.web.filter.CharacterEncodingFilter</filter-class> <init-param> <param-name>charset</param-name> <param-value>UTF-8</param-value> </init-param> </filter> <filter-mapping> <filter-name>CharacterEncodingFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>
二、禁止瀏覽器快取所有動態頁面
有3 個HTTP 響應頭欄位都可以禁止瀏覽器快取當前頁面，它們在 Servlet 中的示例程式碼如下：
1 response.setDateHeader("Expires",-1);
2 response.setHeader("Cache-Control","no-cache");
3 response.setHeader("Pragma","no-cache");
並不是所有的瀏覽器都能完全支援上面的三個響應頭，因此最好是同時使用上面的三個響應頭。
- Expires資料頭：值為GMT時間值，為-1指瀏覽器不要快取頁面
- Cache-Control響應頭有兩個常用值：
- no-cache指瀏覽器不要快取當前頁面。
- max-age:xxx指瀏覽器快取頁面xxx秒。
package me.gacl.web.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;
/**
* @ClassName: NoCacheFilter
* @Description: 禁止瀏覽器快取所有動態頁面
* @author: 孤傲蒼狼
* @date: 2014-8-31 下午11:25:40
*
*/
public class NoCacheFilter implements Filter {
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
//把ServletRequest強轉成HttpServletRequest
HttpServletRequest request = (HttpServletRequest) req;
//把ServletResponse強轉成HttpServletResponse
HttpServletResponse response = (HttpServletResponse) resp;
//禁止瀏覽器快取所有動態頁面
response.setDateHeader("Expires", -1);
response.setHeader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");
chain.doFilter(request, response);
}
public void init(FilterConfig filterConfig) throws ServletException {
}
public void destroy() {
}
}web.xml檔案中的配置如下：
<filter>
<filter-name>NoCacheFilter</filter-name>
<filter-class>me.gacl.web.filter.NoCacheFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>NoCacheFilter</filter-name>
<!--只攔截Jsp請求-->
<servlet-name>*.jsp</servlet-name>
</filter-mapping>三、控制瀏覽器快取頁面中的靜態資源
有些動態頁面中引用了一些圖片或css檔案以修飾頁面效果，這些圖片和css檔案經常是不變化的，所以為減輕伺服器的壓力，可以使用filter控制瀏覽器快取這些檔案，以提升伺服器的效能。
package me.gacl.web.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;
/**
* @ClassName: CacheFilter
* @Description: 控制快取的filter
* @author: 孤傲蒼狼
* @date: 2014-9-1 下午9:39:38
*
*/
public class CacheFilter implements Filter {
private FilterConfig filterConfig;
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) resp;
//1.獲取使用者想訪問的資源
String uri = request.getRequestURI();
//2.得到使用者想訪問的資源的字尾名
String ext = uri.substring(uri.lastIndexOf(".")+1);
//得到資源需要快取的時間
String time = filterConfig.getInitParameter(ext);
if(time!=null){
long t = Long.parseLong(time)*3600*1000;
//設定快取
response.setDateHeader("expires", System.currentTimeMillis() + t);
}
chain.doFilter(request, response);
}
public void init(FilterConfig filterConfig) throws ServletException {
this.filterConfig = filterConfig;
}
public void destroy() {
}
}web.xml檔案中的配置如下：
<!-- 配置快取過濾器 -->
<filter>
<filter-name>CacheFilter</filter-name>
<filter-class>me.gacl.web.filter.CacheFilter</filter-class>
<!-- 配置要快取的web資源以及快取時間，以小時為單位 -->
<init-param>
<param-name>css</param-name>
<param-value>4</param-value>
</init-param>
<init-param>
<param-name>jpg</param-name>
<param-value>1</param-value>
</init-param>
<init-param>
<param-name>js</param-name>
<param-value>4</param-value>
</init-param>
<init-param>
<param-name>png</param-name>
<param-value>4</param-value>
</init-param>
</filter>
<!-- 配置要快取的web資源的字尾-->
<filter-mapping>
<filter-name>CacheFilter</filter-name>
<url-pattern>*.jpg</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>CacheFilter</filter-name>
<url-pattern>*.css</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>CacheFilter</filter-name>
<url-pattern>*.js</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>CacheFilter</filter-name>
<url-pattern>*.png</url-pattern>
</filter-mapping>四、實現使用者自動登陸
思路是這樣的：
1、在使用者登陸成功後，傳送一個名稱為user的cookie給客戶端，cookie的值為使用者名稱和md5加密後的密碼。 2、編寫一個AutoLoginFilter，這個filter檢查使用者是否帶有名稱為user的cookie來，如果有，則呼叫dao查詢cookie的使用者名稱和密碼是否和資料庫匹配，匹配則向session中存入user物件（即使用者登陸標記），以實現程式完成自動登陸。
核心程式碼如下：
處理使用者登入的控制器：LoginServlet
package me.gacl.web.controller;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import me.gacl.dao.UserDao;
import me.gacl.domain.User;
import me.gacl.util.WebUtils;
public class LoginServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String username = request.getParameter("username");
String password = request.getParameter("password");
UserDao dao = new UserDao();
User user = dao.find(username, password);
if(user==null){
request.setAttribute("message", "使用者名稱或密碼不對！！");
request.getRequestDispatcher("/message.jsp").forward(request, response);
return;
}
request.getSession().setAttribute("user", user);
//傳送自動登陸cookie給客戶端瀏覽器進行儲存
sendAutoLoginCookie(request,response,user);
request.getRequestDispatcher("/index.jsp").forward(request, response);
}
/**
* @Method: sendAutoLoginCookie
* @Description: 傳送自動登入cookie給客戶端瀏覽器
* @Anthor:孤傲蒼狼
*
* @param request
* @param response
* @param user
*/
private void sendAutoLoginCookie(HttpServletRequest request, HttpServletResponse response, User user) {
if (request.getParameter("logintime")!=null) {
int logintime = Integer.parseInt(request.getParameter("logintime"));
//建立cookie,cookie的名字是autologin，值是使用者登入的使用者名稱和密碼，使用者名稱和密碼之間使用.進行分割，密碼經過md5加密處理
Cookie cookie = new Cookie("autologin",user.getUsername() + "." + WebUtils.md5(user.getPassword()));
//設定cookie的有效期
cookie.setMaxAge(logintime);
//設定cookie的有效路徑
cookie.setPath(request.getContextPath());
//將cookie寫入到客戶端瀏覽器
response.addCookie(cookie);
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}處理使用者自動登入的過濾器：AutoLoginFilter
package me.gacl.web.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.Cookie;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import me.gacl.dao.UserDao;
import me.gacl.domain.User;
import me.gacl.util.WebUtils;
public class AutoLoginFilter implements Filter {
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest request = (HttpServletRequest) req;
HttpServletResponse response = (HttpServletResponse) resp;
//如果已經登入了，就直接chain.doFilter(request, response)放行
if(request.getSession().getAttribute("user")!=null){
chain.doFilter(request, response);
return;
}
//1.得到使用者帶過來的authlogin的cookie
String value = null;
Cookie cookies[] = request.getCookies();
for(int i=0;cookies!=null && i<cookies.length;i++){
if(cookies[i].getName().equals("autologin")){
value = cookies[i].getValue();
}
}
//2.得到 cookie中的使用者名稱和密碼
if(value!=null){
String username = value.split("\\.")[0];
String password = value.split("\\.")[1];
//3.呼叫dao獲取使用者對應的密碼
UserDao dao = new UserDao();
User user = dao.find(username);
String dbpassword = user.getPassword();
//4.檢查使用者帶過來的md5的密碼和資料庫中的密碼是否匹配,如匹配則自動登陸
if(password.equals(WebUtils.md5(dbpassword))){
request.getSession().setAttribute("user", user);
}
}
chain.doFilter(request, response);
}
public void destroy() {
}
public void init(FilterConfig filterConfig) throws ServletException {
}
}如果想取消自動登入，那麼可以在使用者登出時刪除自動登入cookie，核心程式碼如下：
package me.gacl.web.controller;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class CancelAutoLoginServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//移除儲存在session中的user
request.getSession().removeAttribute("user");
//移除自動登入的cookie
removeAutoLoginCookie(request,response);
//登出使用者後跳轉到登入頁面
request.getRequestDispatcher("/login.jsp").forward(request, response);
}
/**
* @Method: removeAutoLoginCookie
* @Description: 刪除自動登入cookie，
* JavaWeb中刪除cookie的方式就是新建立一個cookie，新建立的cookie與要刪除的cookie同名，
* 設定新建立的cookie的cookie的有效期設定為0，有效路徑與要刪除的cookie的有效路徑相同
* @Anthor:孤傲蒼狼
*
* @param request
* @param response
*/
private void removeAutoLoginCookie(HttpServletRequest request, HttpServletResponse response) {
//建立一個名字為autologin的cookie
Cookie cookie = new Cookie("autologin","");
//將cookie的有效期設定為0，命令瀏覽器刪除該cookie
cookie.setMaxAge(0);
//設定要刪除的cookie的path
cookie.setPath(request.getContextPath());
response.addCookie(cookie);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}