Filter过滤器

Filter过滤器：用来过滤网站的数据。

• 处理中文乱码
• 登录严重

编写步骤：

1.导包

注意不要导错了：

 2.编写过滤器：

1.写servlet

public class ShowServlet extends HttpServlet{
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doGet(req, resp);
    }
 
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}

2.编写过滤器

public class CharacterEncodingFilter implements Filter {
    @Override
    //初始化：web服务器启动，就已经初始化了，随时等待过滤对象出现！
    public void init(FilterConfig filterConfig) throws ServletException {
        System.out.println("初始化");
    }
 
    @Override
    //Chain：链
    /*
     1.过滤器中的所有代码，在过滤特定请求的时候都会执行
     2.chain.doFilter(request,response);意思是让过滤器继续通行
     */
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        //中文乱码过滤器
        servletRequest.setCharacterEncoding("utf-8");
        servletResponse.setCharacterEncoding("utf-8");
        servletResponse.setContentType("test/html;charset=UTF-8");
 
        System.out.println("CharacterEncodingFilter执行前.....");
        filterChain.doFilter(servletRequest,servletResponse); //让我们的请求继续走，如果不写，程序到这里就被拦截停止！
        System.out.println("CharacterEncodingFilter执行后.....");
    }
 
    @Override
    public void destroy() {
        System.out.println("销毁..");
    }
}

3.编写web.xml

"1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
    
    <servlet>
        <servlet-name>ShowServletservlet-name>
        <servlet-class>com.cheng.servlet.ShowServletservlet-class>
    servlet>
    
    <servlet-mapping>
        <servlet-name>ShowServletservlet-name>
        <url-pattern>/servlet/showurl-pattern>
    servlet-mapping>
    
    <filter>
        <filter-name>CharacterEncodingFilterfilter-name>
        <filter-class>src.com.gxa.file.CharacterEncodingFilterfilter-class>
    filter>
    <filter-mapping>
        <filter-name>CharacterEncodingFilterfilter-name>
        
        <url-pattern>/servlet/*url-pattern>
 
    filter-mapping>
web-app>