深入分析JavaWeb 37 -- 过滤器Filter典型應用
一、统一全站字符编码
通过配置参数charset指明使用何种字符编码,以处理Html Form请求参数的中文问题
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: 此过滤器用来解决全站中文乱码问题 * @author: 孤傲苍狼 * @date: 2014-8-31 下午11:09:37 * */
public class CharacterEncodingFilter implements Filter {
private FilterConfig filterConfig = null;
//设置默认的字符编码
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 {
//得到过滤器的初始化配置信息
this.filterConfig = filterConfig;
}
public void destroy() {
}
}
/* 1.实现与被增强对象相同的接口 2、定义一个变量记住被增强对象 3、定义一个构造器，接收被增强对象 4、覆盖需要增强的方法 5、对于不想增强的方法，直接调用被增强对象（目标对象）的方法 */
class MyCharacterEncodingRequest extends HttpServletRequestWrapper{
private HttpServletRequest request;
public MyCharacterEncodingRequest(HttpServletRequest request) {
super(request);
this.request = request;
}
/* 重写getParameter方法 * @see javax.servlet.ServletRequestWrapper#getParameter(java.lang.String) */
@Override
public String getParameter(String name) {
try{
//获取参数的值
String value= this.request.getParameter(name);
if(value==null){
return null;
}
//如果不是以get方式提交数据的，就直接返回获取到的值
if(!this.request.getMethod().equalsIgnoreCase("get")) {
return value;
}else{
//如果是以get方式提交数据的，就对获取到的值进行转码处理
value = new String(value.getBytes("ISO8859-1"),this.request.getCharacterEncoding());
return value;
}
}catch (Exception e) {
throw new RuntimeException(e);
}
}
}web.xml文件中的配置如下：
<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、禁止浏览器缓存所有动态页面
有3 个HTTP 响应头字段都可以禁止浏览器缓存当前页面，它们在 Servlet 中的示例代码如下：
response.setDateHeader("Expires",-1);
response.setHeader("Cache-Control","no-cache");
response.setHeader("Pragma","no-cache"); 并不是所有的浏览器都能完全支持上面的三个响应头，因此最好是同时使用上面的三个响应头。
- Expires数据头：值为GMT时间值，为-1指浏览器不要缓存页面
- Cache-Control响应头有两个常用值：
- no-cache指浏览器不要缓存当前页面。
- max-age:xxx指浏览器缓存页面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: 禁止浏览器缓存所有动态页面 * @author: 孤傲苍狼 * @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强转成HttpServletRequest
HttpServletRequest request = (HttpServletRequest) req;
//把ServletResponse强转成HttpServletResponse
HttpServletResponse response = (HttpServletResponse) resp;
//禁止浏览器缓存所有动态页面
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文件中的配置如下：
<filter>
<filter-name>NoCacheFilter</filter-name>
<filter-class>me.gacl.web.filter.NoCacheFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>NoCacheFilter</filter-name>
<!--只拦截Jsp请求-->
<servlet-name>*.jsp</servlet-name>
</filter-mapping>三、控制浏览器缓存页面中的静态资源
有些动态页面中引用了一些图片或css文件以修饰页面效果，这些图片和css文件经常是不变化的，所以为减轻服务器的压力，可以使用filter控制浏览器缓存这些文件，以提升服务器的性能。
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: 控制缓存的filter * @author: 孤傲苍狼 * @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.获取用户想访问的资源
String uri = request.getRequestURI();
//2.得到用户想访问的资源的后缀名
String ext = uri.substring(uri.lastIndexOf(".")+1);
//得到资源需要缓存的时间
String time = filterConfig.getInitParameter(ext);
if(time!=null){
long t = Long.parseLong(time)*3600*1000;
//设置缓存
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文件中的配置如下：
<!-- 配置缓存过滤器 -->
<filter>
<filter-name>CacheFilter</filter-name>
<filter-class>me.gacl.web.filter.CacheFilter</filter-class>
<!-- 配置要缓存的web资源以及缓存时间，以小时为单位 -->
<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>
<!-- 配置要缓存的web资源的后缀-->
<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、实现用户自动登陆
思路是这样的：
1、在用户登陆成功后，发送一个名称为user的cookie给客户端，cookie的值为用户名和md5加密后的密码。
2、编写一个AutoLoginFilter，这个filter检查用户是否带有名称为user的cookie来，如果有，则调用dao查询cookie的用户名和密码是否和数据库匹配，匹配则向session中存入user对象（即用户登陆标记），以实现程序完成自动登陆。
核心代码如下：
处理用户登录的控制器：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", "用户名或密码不对！！");
request.getRequestDispatcher("/message.jsp").forward(request, response);
return;
}
request.getSession().setAttribute("user", user);
//发送自动登陆cookie给客户端浏览器进行存储
sendAutoLoginCookie(request,response,user);
request.getRequestDispatcher("/index.jsp").forward(request, response);
}
/** * @Method: sendAutoLoginCookie * @Description: 发送自动登录cookie给客户端浏览器 * @Anthor:孤傲苍狼 * * @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"));
//创建cookie,cookie的名字是autologin，值是用户登录的用户名和密码，用户名和密码之间使用.进行分割，密码经过md5加密处理
Cookie cookie = new Cookie("autologin",user.getUsername() + "." + WebUtils.md5(user.getPassword()));
//设置cookie的有效期
cookie.setMaxAge(logintime);
//设置cookie的有效路径
cookie.setPath(request.getContextPath());
//将cookie写入到客户端浏览器
response.addCookie(cookie);
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}处理用户自动登录的过滤器：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;
//如果已经登录了，就直接chain.doFilter(request, response)放行
if(request.getSession().getAttribute("user")!=null){
chain.doFilter(request, response);
return;
}
//1.得到用户带过来的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中的用户名和密码
if(value!=null){
String username = value.split("\\.")[0];
String password = value.split("\\.")[1];
//3.调用dao获取用户对应的密码
UserDao dao = new UserDao();
User user = dao.find(username);
String dbpassword = user.getPassword();
//4.检查用户带过来的md5的密码和数据库中的密码是否匹配,如匹配则自动登陆
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 {
}
}如果想取消自动登录，那么可以在用户注销时删除自动登录cookie，核心代码如下：
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 {
//移除存储在session中的user
request.getSession().removeAttribute("user");
//移除自动登录的cookie
removeAutoLoginCookie(request,response);
//注销用户后跳转到登录页面
request.getRequestDispatcher("/login.jsp").forward(request, response);
}
/** * @Method: removeAutoLoginCookie * @Description: 删除自动登录cookie， * JavaWeb中删除cookie的方式就是新创建一个cookie，新创建的cookie与要删除的cookie同名， * 设置新创建的cookie的cookie的有效期设置为0，有效路径与要删除的cookie的有效路径相同 * @Anthor:孤傲苍狼 * * @param request * @param response */
private void removeAutoLoginCookie(HttpServletRequest request, HttpServletResponse response) {
//创建一个名字为autologin的cookie
Cookie cookie = new Cookie("autologin","");
//将cookie的有效期设置为0，命令浏览器删除该cookie
cookie.setMaxAge(0);
//设置要删除的cookie的path
cookie.setPath(request.getContextPath());
response.addCookie(cookie);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}以上就是过滤器的几个常见应用场景。