Filter (Filter)

目录

一、如何使用过滤器（Filter）

二、通过xml配置过滤器

三、通过注解配置过滤器

四、Get the initialization parameters of the filter configuration

五、过滤器的使用

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一、如何使用过滤器（Filter）

1.1.写一个类实现（implements）Filter（过滤器类,Filter来自 Filter - javax,servlet接口中）.

1.2.重写三个方法

@Override
public void destroy() {
   System.out.println("过滤器被销毁！");
}

@Override
public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
         throws IOException, ServletException {
   System.out.println("The request was intercepted by the filter！");
}
    
@Override
public void init(FilterConfig arg0) throws ServletException {
   // 启动Tomcat服务
   System.out.println("过滤器初始化/过滤器被创建！");
}

二、通过xml配置过滤器

<!-- 配置过滤器 -->
  <filter>
      <filter-name>loginFilter</filter-name>
      <filter-class>com.zking.filter.LoginFilter</filter-class>
      <!-- Configure filter initialization parameters -->
      <!-- 参数1 -->
      <init-param>
          <!-- 参数名 -->
          <param-name>name</param-name>
          <!-- 参数值 -->
          <param-value>张三</param-value>
      </init-param>
      <!-- 参数2 -->
      <init-param>
          <!-- 参数名 -->
          <param-name>sex</param-name>
          <!-- 参数值 -->
          <param-value>男</param-value>
      </init-param>
  </filter>
<!-- Configure the filter map file -->
  <filter-mapping>
      <filter-name>loginFilter</filter-name>
     <!-- Set the request to filter by the filter -->
      <!-- 1.filter a single request -->
      <url-pattern>/index.jsp</url-pattern>
      <!-- 2.Filter requests with the specified suffix -->
      <!-- 如：Filter all suffix names.jsp的页面 -->
      <url-pattern>*.jsp</url-pattern>
      <!-- 3.Filter requests for the specified directory -->
      <url-pattern>/home/index.jsp</url-pattern>
      <!-- 4.Filter all requests for the entire project -->
      <url-pattern>/*</url-pattern>
  </filter-mapping>

三、通过注解配置过滤器

3.1.Configure to filter individual requests

@WebFilter("/index.jsp")

3.2.Configure to filter multiple requests

@WebFilter(
            filterName = "loginFilter",// Configure the filter name,相当于<filter-name>loginFilter</filter-name>
            urlPatterns = {"/login.jsp","/index.jsp"},// Configure to filter multiple pages
            // 配置初始化参数
            initParams = {
                    @WebInitParam(name = "name",value = "张三"),
                    @WebInitParam(name = "sex",value = "男")
            }
        )

四、Get the initialization parameters of the filter configuration

    // Get the initialization parameters of the configuration in the initialization method
    @Override
    public void init(FilterConfig arg0) throws ServletException {
        // 启动Tomcat服务
        System.out.println("过滤器初始化/过滤器被创建！");
        
        // 获取配置的初始化参数
        String name = arg0.getInitParameter("name");
        String sex = arg0.getInitParameter("sex");
        System.out.println("name = " + name);
        System.out.println("sex = " + sex);
        
    }

五、过滤器的使用

1.转换参数arg0和arg1（要使用request和response里面的方法）
HttpServletRequest req = (HttpServletRequest)arg0;
HttpServletResponse resp = (HttpServletResponse)arg1;
        
2.设置编码
req.setCharacterEncoding("utf-8");
resp.setContentType("html/text;charset=utf-8");

3.使用arg2.doFilter(arg0, arg1),The page blocked by the filter can continue to function normally.

public void doFilter(ServletRequest arg0, ServletResponse arg1, FilterChain arg2)
            throws IOException, ServletException {
        System.out.println("The request was intercepted by the filter！");
        
        // 转换参数arg0和arg1
        HttpServletRequest req = (HttpServletRequest)arg0;
        HttpServletResponse resp = (HttpServletResponse)arg1;
        
        // 设置编码
        resp.setContentType("html/text;charset=utf-8");
        
        
        // 放行/继续前进
        arg2.doFilter(arg0, arg1);
    }

完