过滤器

过滤器: 定义在服务器端的一段程序, 可以截获客户端发来的请求, 并根据一定规则进行过滤和拦截

过滤器的生命周期:
服务器启动
先通过web.xml加载过滤器进行实例化(这个过程是调用过滤器中init()方法, 同样也是只执行一次)
客户端发送请求:
执行过滤器中的doFilter()方法, 这个方法会执行N次, 每次有请求发送过来, 都会执行这个方法进行过滤
销毁过程
同servlet, 关闭或者停止服务器的时候会执行destory()方法

过滤器链:
不同的请求互不影响
过滤器链主要是针对多个过滤器过滤同一个url请求
过滤器的先后顺序是按照在web.xml的配置顺序来的
运行顺序: 请求--->过滤器1过滤--->过滤器2过滤--->后台处理层--->过滤器2过滤--->过滤器1过滤--->客户端接收

3.0新特性的过滤器:
使用注解的方式:
@WebFilter(filterName="", value={"",""}...等其他配置)

login.jsp

<from type="LoginServler" method="post">
        用户名：<input type="text" name="username" /><br>
        密码：   <input type="text" name="password" /><br>
        <input type="submit" value="登录" />
</from> 

register.jsp

<from type="RegisterServler" method="post">
         用户名: <input type="text" name="username" /><br>
         密码:   <input type="text" name="password" /><br>
         姓名：    <input type="text" name="realname" /><br>
         <input type="submit" value="提交" />
</from>

LoginServler.java

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        System.out.println(username);
        System.out.println(password);
        
        if("admin".equals(username) && "123456".equals(password)){
            request.getSession().setAttribute("currentUser","admin");
            response.sendRedirect("index.jsp");
        }else{
            response.sendRedirect("fail.jsp");
        }
    }

RegisterServler.java

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        String username = request.getParameter("username");
        String password = request.getParameter("password");
        System.out.println(username);
        System.out.println(password);
        
        if("admin".equals(username) && "123456".equals(password)){
            request.getSession().setAttribute("currentUser","admin");
            response.sendRedirect("index.jsp");
        }else{
            response.sendRedirect("fail.jsp");
        }
    }

SessionFilterTest.java

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;

public class SessionFilterTest implements Filter {

    private String pages;
    private HttpServletRequest request;
    
    @Override
    public void destroy() {
        
    }

    @Override
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain)
            throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest)req;
        HttpServletResponse response = (HttpServletResponse)resp;
        
        //获取当前的请求
        String uri = request.getRequestURI();
        System.out.println("当前发送的请求"+uri);
        
        //获取不需要判断session的请求
        String[] _pages = pages.split(";");
        
        //判断当前请求是否在不需要判断的请求里
        if(checkString(_pages,uri)){
            //放行
            chain.doFilter(req,resp);
            
        }else{
            //先判断session在放行
            Object obj = request.getSession().getAttribute("currentUser");
            if(obj==null){
                response.sendRedirect("login.jsp");
            }else{
                chain.doFilter(req,resp);
            }
        }
    }
    public static boolean checkString(String[] pages,String uri){
        for(String s:pages){
            if(uri.contains(s)){
                return true;
            }
        }
        return false;
    }

    @Override
    public void init(FilterConfig config) throws ServletException {
        String str = config.getInitParameter("page");
        this.setPages(str);
        System.out.println(str);
        
    }
    public String getPages(){
        return pages;
    }
    public void setPages(String pages){
        this.pages = pages;
    }

}

TestFilter.java

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;

public class TestFilter implements Filter {

    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain arg2)
            throws IOException, ServletException {
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html; charset=utf-8");
        
        arg2.doFilter(request, response);
        
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        // TODO Auto-generated method stub
        
    }

}