Filter--基础知识

1.Servlet API 定义三个接口类：Filter FilterChain 和FilterConfig，由Servlet容器进行调用和执行

 1. 创建一个Filter l类

  2.在web.xml 进行配置，url-pattern-->指定的要拦截的Jsp 资源

 3. init() 对其进行初始化同时对其进行初始化

    过滤请求 调用doFilter

FilterChain： 构成一个Filter链子 只有一个doFilter() 方法   便请求传递给下一个Filter，如果Filter最后一个传递给对象 ，多个Filter执行顺序与在<filter-mapping> 配置的顺序有关，Filter没有类继承只能直接实现接口

例子：

在Servlet3.0特性中，不需要在web.xml上去进行配置，直接在@WebFilter() 就行  

  但是其执行的顺序在web.xml中按照filter-mapping 但是在Servlet3.0特性中按照的 filter文件名.java 的首字母顺序执行  UserName.java 执行在passwordFilter.java 之后，所有我们调换其首字母

package com.FilterTest;

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.annotation.WebFilter;
import javax.servlet.annotation.WebInitParam;

/**
 * Servlet Filter implementation class UserNameFilter
 */
@WebFilter( filterName="A",urlPatterns="/hello.jsp",
  initParams={@WebInitParam(name="username", value="Tom")})
public class UserNameFilter implements Filter {

    /**
     * Default constructor. 
     */
    public UserNameFilter() {
        // TODO Auto-generated constructor stub
    }

    /**
     * @see Filter#destroy()
     */
    public void destroy() {
        // TODO Auto-generated method stub
    }

    /**
     * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
     */
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        // TODO Auto-generated method stub
        // place your code here
        System.out.println("doFilter");
        
        // 先对用户进行验证 输入的username与初始化设置username是否相等
        String initUser=filterconfig.getInitParameter("username");
        System.out.println(initUser);
        String username=request.getParameter("username");
        
        if(!username.equals(initUser))
        {
            //就让其前往passwordFilter页面
            request.setAttribute("message", "用户名不正确");
            request.getRequestDispatcher("/testa.jsp").forward(request, response);
             return;
        }
        // pass the request along the filter chain passwordFilter
        chain.doFilter(request, response);
    }
    private FilterConfig filterconfig;
    /**
     * @see Filter#init(FilterConfig)
     */
    public void init(FilterConfig fConfig) throws ServletException {
        // TODO Auto-generated method stub
        this.filterconfig=fConfig;
    }

}

 

<form action="hello.jsp" method="post">
                  username:<input type="text" name="username" value="${ param.username}"/>
                  password:<input type="text" name="password"/>
                  <input type="submit" name="submit"/>
            </form>    
        <font color="red" >${message }</font>

编写HttpFilter 让原生ServletRequest 变成HttpServletRequest

package com.FilterTest;

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;

/**将Filter 进行封装，将其转换成HttpFilter
 * 自定义的HttpFilter 实现Filter接口*/

public abstract class HttpFilter  implements Filter{

    private FilterConfig filterConfig;
    /**不建议覆盖此方法*/
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
        this.filterConfig=filterConfig;
        init();
    }
    /**
     * 供子类初始化方法 ，可以通过getFilterConfig方法获取对象*/
   protected void init(){};
   
   /**
     * 直接返回 init(ServletConfig) 的 FilterConfig 对象
     */
    public FilterConfig getFilterConfig() {
        return filterConfig;
    }

    public void setFilterConfig(FilterConfig filterConfig) {
        this.filterConfig = filterConfig;
    }

    /**原生的doFilter方法，在内部将ServletRequest 转换成 HttpServletrequest
     * 调用doFilter(HttpServletRequest request, HttpServletResponse response, 
     *        FilterChain filterChain)方法
     *
     *    若编写 Filter 的过滤方法不建议直接继承该方法. 而建议继承
     *    doFilter(HttpServletRequest request, HttpServletResponse response, 
     *        FilterChain filterChain) 方法*/
    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {
        // TODO Auto-generated method stub
        HttpServletRequest request=(HttpServletRequest) req;
        HttpServletResponse response=(HttpServletResponse) req;
        
        doFilter(request,response,chain);
    }
    
     public abstract void doFilter(HttpServletRequest request,HttpServletResponse response,FilterChain chain);
    
     @Override
    public void destroy() {
        // TODO Auto-generated method stub
        
    }

}

 doFilter中执行的顺序是类似于递归调用的方式

6.<dispatcher> 指定Filter拦截的资源被Servlet容器调用的方式：默认的REQUEST,

 如下：如果采用GET、post---->1.jsp----转发-->目的.jsp  ；由于默认是REQUEST则Filter不会对此继续拦截

  必须修改@webFilter中dispatcher属性,这样才能在 通过转发和request方法的访问过程中 加上Filter

     dispatcherTypes={DispatcherType.FORWARD,DispatcherType.FORWARD}

 总结：

---

8.Filter 禁用缓存的：3个Http的响应字段可以禁止浏览器缓存

 直接继承 Filter接口：进行强制转换

((HttpServletResponse) response).setDateHeader("Expires",-1);

9.字符编码的过滤器：

request.setCharacterEncoding("UTF-8");

在过滤器中进行字符编码，到达JSP之前，指定其中字符编码 同时在web.xml 上初始化encoding 的编码方式

package com.FilterTest;

import java.io.UnsupportedEncodingException;

import javax.servlet.FilterChain;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class EncodingFilter extends HttpFilter {

    private String encoding;
    protected void init()
    {
        this.encoding=getFilterConfig().getServletContext().getInitParameter("encoding");
    }
    @Override
    public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) {
        // TODO Auto-generated method stub
        try {
            request.setCharacterEncoding(encoding);
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        doFilter(request,response,chain);
    }

}

package com.FilterTest;

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;

/**将Filter 进行封装，将其转换成HttpFilter
 * 自定义的HttpFilter 实现Filter接口*/

public abstract class HttpFilter  implements Filter{

    private FilterConfig filterConfig;
    /**不建议覆盖此方法*/
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
        this.filterConfig=filterConfig;
        init();
    }
    /**
     * 供子类初始化方法 ，可以通过getFilterConfig方法获取对象*/
   protected void init(){};
   
   /**
     * 直接返回 init(ServletConfig) 的 FilterConfig 对象
     */
    public FilterConfig getFilterConfig() {
        return filterConfig;
    }

    public void setFilterConfig(FilterConfig filterConfig) {
        this.filterConfig = filterConfig;
    }

    /**原生的doFilter方法，在内部将ServletRequest 转换成 HttpServletrequest
     * 调用doFilter(HttpServletRequest request, HttpServletResponse response, 
     *        FilterChain filterChain)方法
     *
     *    若编写 Filter 的过滤方法不建议直接继承该方法. 而建议继承
     *    doFilter(HttpServletRequest request, HttpServletResponse response, 
     *        FilterChain filterChain) 方法*/
    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {
        // TODO Auto-generated method stub
        HttpServletRequest request=(HttpServletRequest) req;
        HttpServletResponse response=(HttpServletResponse) req;
        
        doFilter(request,response,chain);
    }
    
     public abstract void doFilter(HttpServletRequest request,HttpServletResponse response,FilterChain chain);
    
     @Override
    public void destroy() {
        // TODO Auto-generated method stub
        
    }

}

 

10.检测用户是否登录过：

要求 session.getAttribute(key) 这个key在web.xml 配置成 可以配置的方式

 解决方法：系统中某些网页只有登录才能查看，设置一个Filter，当用户没有登录的话则重定向到登录页面

要求：session在检查的关键字做成可以配置的方式

1.URI：/Tomcat/filter/a.jsp

2.URL:http://localhost:8080/TomCat/filter/a.jsp

3.servletPath=/filter/a.jsp  ---服务器内部的地址

以下是代码： 所有list登录经过Fileter进行处理，有些servletPath默认其通过

 1.//1.获取请求的ServletPath

2.// 2.检查servletPath是否不需要检查的url

// 3.从session获取Seesionkey，不存在重新定向到登录页面---比较输入用户名是否正确，DAO在SQL查询并且比较

4. 用户名正确 放行

package com.FilterTest;

import java.io.IOException;
import java.util.Arrays;
import java.util.List;

import javax.servlet.FilterChain;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebFilter("/filter/*")
public class LoginFilter extends HttpFilter {

    //0.从web.xml 文件获取初始值
    private String sessionKey;
    private String redirectUrl;
    private String uncheckedUrls;
    
    @Override
    protected void init()
    {
        // 获取初始化值
        ServletContext servletcontext=getFilterConfig().getServletContext();
        sessionKey=servletcontext.getInitParameter("userSessionKey");
        redirectUrl=servletcontext.getInitParameter("redirectPage");
        uncheckedUrls=servletcontext.getInitParameter("uncheckedUrls");
        
        System.out.println(sessionKey);
        System.out.println(redirectUrl);
        System.out.println(uncheckedUrls);
    }
    @Override
    public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws IOException, ServletException {
        // TODO Auto-generated method stub
        //1.获取请求的ServletPath
        //String requestURI=request.getRequestURI();
        //String requestURl=request.getRequestURL().toString();
        String servletPath=request.getServletPath();
        
        
        // 2.检查servletPath是否不需要检查的url
        List<String> urs=Arrays.asList(uncheckedUrls.split(","));
        if(urs.contains(servletPath))
        {
            // 直接放行

            chain.doFilter(request, response);
            return;
        }
        // 3.从session获取Seesionkey，不存在重新定向到登录页面
        Object user=request.getSession().getAttribute(sessionKey);
        if(user == null){
            response.sendRedirect(request.getContextPath() + redirectUrl);
            return;
        }
        
        // 4.存在直接放行
        chain.doFilter(request, response);
    }

}

package com.FilterTest;

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;

/**将Filter 进行封装，将其转换成HttpFilter
 * 自定义的HttpFilter 实现Filter接口*/

public abstract class HttpFilter  implements Filter{

    private FilterConfig filterConfig;
    /**不建议覆盖此方法*/
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
        this.filterConfig=filterConfig;
        init();
    }
    /**
     * 供子类初始化方法 ，可以通过getFilterConfig方法获取对象*/
   protected void init(){};
   
   /**
     * 直接返回 init(ServletConfig) 的 FilterConfig 对象
     */
    public FilterConfig getFilterConfig() {
        return filterConfig;
    }

    public void setFilterConfig(FilterConfig filterConfig) {
        this.filterConfig = filterConfig;
    }

    /**原生的doFilter方法，在内部将ServletRequest 转换成 HttpServletrequest
     * 调用doFilter(HttpServletRequest request, HttpServletResponse response, 
     *        FilterChain filterChain)方法
     *
     *    若编写 Filter 的过滤方法不建议直接继承该方法. 而建议继承
     *    doFilter(HttpServletRequest request, HttpServletResponse response, 
     *        FilterChain filterChain) 方法*/
    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {
        // TODO Auto-generated method stub
        HttpServletRequest request=(HttpServletRequest) req;
        HttpServletResponse response=(HttpServletResponse) res;
        
        doFilter(request,response,chain);
    }
    
     public abstract void doFilter(HttpServletRequest request,HttpServletResponse response,FilterChain chain) throws IOException, ServletException;
    
     @Override
    public void destroy() {
        // TODO Auto-generated method stub
        
    }

}

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <context-param>
    <param-name>password</param-name>
    <param-value>1234</param-value>
  </context-param>
  
  <!-- 用户信息登录放入到Ssesion的值 -->
  <context-param>
              <param-name>userSessionKey</param-name>
              <param-value>USERSESSIONKEY</param-value>
  </context-param>
  
   <!-- 没有登录重定向页面 可以配置，成灵活的-->
   <context-param>
                   <param-name>redirectPage</param-name>
                 <param-value>/filter/login.jsp</param-value>
   </context-param>
   <!-- 不需要拦截页面，自由访问 -->
   <context-param>
                   <param-name>uncheckedUrls</param-name>
                 <param-value>/filter/login.jsp,/filter/a.jsp,/filter/list.jsp,/filter/dologin.jsp</param-value>
   </context-param>
</web-app>