过滤器Filter

发表于 更新于 分类于 阅读次数： Valine：

过滤器基本知识

image-20220412155509142

这是源代码，并没有对操作进行任何的限制

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@WebServlet("/demo01.hi")
public class Test extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("demo01 is ing");
        req.getRequestDispatcher("fruit/demo01.html").forward(req,resp);
    }
}

下面进行限制，进行过滤

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@WebFilter("/demo01.hi")
public class Demo01Filter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        Filter.super.init(filterConfig);
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("我要放行给servlet");
        //以上使servlet之前
        filterChain.doFilter(servletRequest,servletResponse);

        System.out.println("我要放行给浏览器");
    }

    @Override
    public void destroy() {
        Filter.super.destroy();
    }
}

同时servlet也可以进行通配符设置等等，和servlet相同

过滤器链

在servlet之前，可以含有多个过滤器对其进行检查过滤，最终交给servlet执行。而过滤器链的运行是按照他的全类名顺序进行运行，但是如果在配置文件中进行了过滤器的定义，那么就是按照定义的顺序进行

image-20220412165340064

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package com.zss.filter;

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

public class filter01 implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        Filter.super.init(filterConfig);
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        System.out.println("我是01");
        filterChain.doFilter(servletRequest,servletResponse);
        System.out.println("01走了");
    }

    @Override
    public void destroy() {
        Filter.super.destroy();
    }
}

image-20220412165416284

在前面的小项目中在过滤器中设置编码

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@Override
public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

    servletRequest.setCharacterEncoding("UTF-8");

    filterChain.doFilter(servletRequest,servletResponse);
}