建立攔截器類,需要實現javax.servlet.Filter介面

public class FilterDemo1 implements Filter {
    @Override
    public void init(FilterConfig arg0) throws ServletException {
        System.err.println("伺服器啟動時呼叫此方法,只調用一次,用來初始化");
    }
    @Override
    public void destroy() {
        System.err.println("伺服器退出時呼叫此方法,只調用一次"
 
);
    }
    @Override
    public void doFilter(ServletRequest arg0, ServletResponse arg1,
        HttpServletRequest request = (HttpServletRequest) arg0;
        HttpServletResponse response = (HttpServletResponse) arg1;
        MyRequest request1 = new MyRequest(request);
        //設定request的編碼方式
        request1.setCharacterEncoding("utf-8"
 
);
        //解除攔截
        chain.doFilter(request1, response);
    }

自定義內部類,繼承HttpServletRequestWrapper類
注:HttpServletRequestWrapper類實現了HttpServletRequest介面,重寫了介面方法

class MyRequest extends HttpServletRequestWrapper{
        private HttpServletRequest request ;
        public MyRequest(HttpServletRequest request) {
            super
 
(request);
            this.request = request;
        }

        @Override
        public String getParameter(String name) {
            String value = request.getParameter(name);
            //判Null空
            if(value==null){
                return null;
            }
            //判請求方式
            if(request.getMethod().equalsIgnoreCase("POST")){
                return value;
            }
            try {
                //轉換編碼方式
                value = new String(value.getBytes("ISO-8859-1"),"utf-8");
            } catch (UnsupportedEncodingException e) {
                throw new RuntimeException(e);
            }
            return value;
        }
    }

在web.xml配置檔案中載入Filter攔截器

    <filter>
        <filter-name>FilterDemo1</filter-name>
        <filter-class>filter.demo.FilterDemo1</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>FilterDemo1</filter-name>
        <!-- /*為攔截所有請求 -->
        <url-pattern>/*</url-pattern>
    </filter-mapping>