【Head First Servlets and JSP】筆記 28： 過濾器與封裝器

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1、過濾器的執行順序： <url-pattern> 為第一梯隊， <servlet-name> 為第二梯隊，梯隊內的執行順序和 DD 裡的聲明順序相同。

When the container recives a request, it first finds all the filter mappings with a <url-pattern> that matches the request URI. This becomes the first set of filters in the filter chain.Next it finds all the filter mappings with a <servlet-name> that matches the request URI. This becomes the second set of filters in the filter chain.In both the sets the filters are executed in the order in which they are declared in the D.D.

 

2、可以對伺服器中傳遞的請求進行過濾。

    <filter>        <filter-name>BeerRequest</filter-name>        <filter-class>sample.BeerRequestFilter</filter-class>        <init-param>            <param-name>LogFileName</param-name>            <param-value>Userlog.txt</param-value>        </init-param>    </filter>    <filter-mapping>        <filter-name>BeerRequest</filter-name>        <url-pattern>*.do</url-pattern>        <servlet-name>jack</servlet-name>        <dispatcher>REQUEST</dispatcher> <!-- 當一個也沒有設定時，它是預設值 -->        <dispatcher>INCLUDE</dispatcher>        <dispatcher>FORWARD</dispatcher>        <dispatcher>ERROR</dispatcher>    </filter-mapping>

 

3、過濾器應用執行個體

package sample;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;import java.io.PrintWriter;public class Servlet extends HttpServlet {    @Override    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        PrintWriter printWriter = resp.getWriter();        printWriter.println("calls doGet(req, resp)");        printWriter.println("測試能否輸出中文");        printWriter.close();    }}

filter ：

package sample;import javax.servlet.*;import java.io.IOException;public class Filter implements javax.servlet.Filter{    private int visited;    @Override    public void init(FilterConfig filterConfig) throws ServletException {    }    @Override    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {        servletResponse.setContentType("text/html");        servletResponse.setCharacterEncoding("utf-8");        visited ++;        filterChain.doFilter(servletRequest, servletResponse);        System.out.println("visited = " + visited);    }    @Override    public void destroy() {    }}

web.xml

<?xml version="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_3_1.xsd"         version="3.1">    <servlet>        <servlet-name>servlet</servlet-name>        <servlet-class>sample.Servlet</servlet-class>    </servlet>    <servlet-mapping>        <servlet-name>servlet</servlet-name>        <url-pattern>/do</url-pattern>    </servlet-mapping>    <filter>        <filter-name>filter</filter-name>        <filter-class>sample.Filter</filter-class>    </filter>    <filter-mapping>        <filter-name>filter</filter-name>        <servlet-name>servlet</servlet-name>    </filter-mapping></web-app>

 

4、封裝器略。

 

 

 

【Head First Servlets and JSP】筆記 28： 過濾器與封裝器