JavaWeb总结（十）

Filter配置详解

web项目目录示意图

<!-- Filter配置 -->  
  <filter>
    <display-name>Filter_one</display-name>
    <filter-name>Filter_one</filter-name>
    <filter-class>com.my.filter.Filter_one</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>Filter_one</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <filter>
    <display-name>Filter_two</display-name>
    <filter-name>Filter_two</filter-name>
    <filter-class>com.my.filter.Filter_two</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>Filter_two</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <filter>
    <display-name>Filter_three</display-name>
    <filter-name>Filter_three</filter-name>
    <filter-class>com.my.filter.Filter_three</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>Filter_three</filter-name>
　　<url-pattern>/*</url-pattern>
  </filter-mapping>

<!-- servlet配置 -->  
  <servlet>
    <description></description>
    <display-name>Servlet_one</display-name>
    <servlet-name>Servlet_one</servlet-name>
    <servlet-class>com.my.servlet.Servlet_one</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Servlet_one</servlet-name>
    <url-pattern>/Servlet_one</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>Servlet_two</display-name>
    <servlet-name>Servlet_two</servlet-name>
    <servlet-class>com.my.servlet.Servlet_two</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Servlet_two</servlet-name>
    <url-pattern>/Servlet_two</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>Servlet_three</display-name>
    <servlet-name>Servlet_three</servlet-name>
    <servlet-class>com.my.servlet.Servlet_three</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Servlet_three</servlet-name>
    <url-pattern>/Servlet_three</url-pattern>
  </servlet-mapping>

 

//Filter_one重写的doFilter语句
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.err.println("Filter_one前====>");
        chain.doFilter(request, response);
        System.err.println("Filter_one后====>");
}
//Filter_two重写的doFilter语句
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.err.println("Filter_two前====>");
        chain.doFilter(request, response);
        System.err.println("Filter_two后====>");
}
//Filter_three重写的doFilter语句
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        System.err.println("Filter_three前====>");
        chain.doFilter(request, response);
        System.err.println("Filter_three后====>");
}
//Servlet_one重写doGet方法
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.err.println("Servlet_one===>");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
}
//Servlet_two重写doGet方法
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.err.println("Servlet_two===>");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
}
//Servlet_three重写doGet方法
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.err.println("Servlet_three===>");
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
}

 

 

已知：过滤器Filter_one、Filter_two、Filter_three都会对Servlet_one进行拦截，那么当我们在浏览器地址输入Servlet_one，客户端会打印什么呢？

输入Servlet_one地址

客户端打印结果

 

传递资源会经过Filter_one、Filter_two、Filter_three三个过滤器，到达Servlet_one，访问结束后响应又会经过Filter_one、Filter_two、Filter_three三个过滤器，所以才有上图的结果

修改Servlet_one代码

 

//Servlet_one重写doGet方法
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
　　System.err.println("Servlet_one===>");    
　　request.getRequestDispatcher("/Servlet_two").forward(request, response);

 

 

重定向到Servlet_two结果又会是怎样呢？结果是如下表左边还是右边呢？

 

Filter_one前====> Filter_two前====> Filter_three前====> Servlet_one===> Servlet_two===> Filter_three后====> Filter_two后====> Filter_one后====>

Filter_one前====> Filter_two前====> Filter_three前====> Servlet_one===> Filter_one前====> Filter_two前====> Filter_three前====> Servlet_two===> Filter_three后====> Filter_two后====> Filter_one后====> Filter_three后====> Filter_two后====> Filter_one后====>

 

结果如上表（结果左）所示

这是为什么呢？过滤器不是对项目内所有文件都要进行过滤吗？为什么这里没有对Servlet_two进行过滤？原因就在这里<dispatcher>标签，内含四个参数：FORWARD、ERROR、INCLUDE、REQUEST；REQUEST为默认标签，并且一个<filter-mapping>内可以包含多个<dispatcher>标签；

修改Filter_one代码

 

  <filter-mapping>
    <filter-name>Filter_one</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>FORWARD</dispatcher>
    <dispatcher>REQUEST</dispatcher>
  </filter-mapping>

 

 

修改后结果如图所示

 

结果示意图

 

这样就可以在Servlet_one跳转到Servlet_two的时候，对Servlet_two也进行过滤。

ERROR参数又有什么作用呢？已知我们在程序调试的时候难免出现异常，或者url路径填写错误，那么网页就会提示这些错误

Error Status 500

Error Status 404

这样的错误提示信息较为相信，明眼人一眼就能看见错误信息，这样你的后台信息就会暴露出来，这样是非常不好。那么怎么替代这些错误信息呢？就要用到<dispatcher>标签中的ERROR参数。

修改Filter_one代码

 

<!--在标签<filter-mapping>中添加子标签<dispatcher>并且参数为ERROR-->
<dispatcher>ERROR</dispatcher>
<!--在标签<web-app>中添加子标签<error-page>-->
  <error-page>
      <!--状态码-->
      <error-code>404</error-code>
      <!--连接路径-->
      <location>/Test/WebContent/jsp/error_404_page.jsp</location>
  </error-page>
    <error-page>
      <error-code>500</error-code>
      <location>/Test/WebContent/jsp/error_500_page.jsp</location>
  </error-page>

 

 

当程序再出现异常的时候，就会跳转到我们自己设计的错误提示页面，不会将源代码错误信息显示在页面上。既美化又更加安全、健壮！

Error Status 500

Error Status 404

 

Filter配置详解

web项目目录示意图

<!-- Filter配置 -->  

  <filter>

    <display-name>Filter_one</display-name>

    <filter-name>Filter_one</filter-name>

    <filter-class>com.my.filter.Filter_one</filter-class>

  </filter>

  <filter-mapping>

    <filter-name>Filter_one</filter-name>

    <url-pattern>/*</url-pattern>

  </filter-mapping>

  <filter>

    <display-name>Filter_two</display-name>

    <filter-name>Filter_two</filter-name>

    <filter-class>com.my.filter.Filter_two</filter-class>

  </filter>

  <filter-mapping>

    <filter-name>Filter_two</filter-name>

    <url-pattern>/*</url-pattern>

  </filter-mapping>

  <filter>

    <display-name>Filter_three</display-name>

    <filter-name>Filter_three</filter-name>

    <filter-class>com.my.filter.Filter_three</filter-class>

  </filter>

  <filter-mapping>

    <filter-name>Filter_three</filter-name>

<url-pattern>/*</url-pattern>

  </filter-mapping>

 

<!-- servlet配置 -->  

  <servlet>

    <description></description>

    <display-name>Servlet_one</display-name>

    <servlet-name>Servlet_one</servlet-name>

    <servlet-class>com.my.servlet.Servlet_one</servlet-class>

  </servlet>

  <servlet-mapping>

    <servlet-name>Servlet_one</servlet-name>

    <url-pattern>/Servlet_one</url-pattern>

  </servlet-mapping>

  <servlet>

    <description></description>

    <display-name>Servlet_two</display-name>

    <servlet-name>Servlet_two</servlet-name>

    <servlet-class>com.my.servlet.Servlet_two</servlet-class>

  </servlet>

  <servlet-mapping>

    <servlet-name>Servlet_two</servlet-name>

    <url-pattern>/Servlet_two</url-pattern>

  </servlet-mapping>

  <servlet>

    <description></description>

    <display-name>Servlet_three</display-name>

    <servlet-name>Servlet_three</servlet-name>

    <servlet-class>com.my.servlet.Servlet_three</servlet-class>

  </servlet>

  <servlet-mapping>

    <servlet-name>Servlet_three</servlet-name>

    <url-pattern>/Servlet_three</url-pattern>

  </servlet-mapping>

 

//Filter_one重写的doFilter语句

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

System.err.println("Filter_one前====>");

chain.doFilter(request, response);

System.err.println("Filter_one后====>");

}

//Filter_two重写的doFilter语句

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

System.err.println("Filter_two前====>");

chain.doFilter(request, response);

System.err.println("Filter_two后====>");

}

//Filter_three重写的doFilter语句

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

System.err.println("Filter_three前====>");

chain.doFilter(request, response);

System.err.println("Filter_three后====>");

}

//Servlet_one重写doGet方法

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

System.err.println("Servlet_one===>");

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

doGet(request, response);

}

//Servlet_two重写doGet方法

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

System.err.println("Servlet_two===>");

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

doGet(request, response);

}

//Servlet_three重写doGet方法

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

System.err.println("Servlet_three===>");

}

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

doGet(request, response);

}

已知：过滤器Filter_one、Filter_two、Filter_three都会对Servlet_one进行拦截，那么当我们在浏览器地址输入Servlet_one，客户端会打印什么呢？

输入Servlet_one地址

客户端打印结果

过滤示意图

传递资源会经过Filter_one、Filter_two、Filter_three三个过滤器，到达Servlet_one，访问结束后响应又会经过Filter_one、Filter_two、Filter_three三个过滤器，所以才有上图的结果。

修改Servlet_one代码

//Servlet_one重写doGet方法 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { System.err.println("Servlet_one===>");request.getRequestDispatcher("/Servlet_two").forward(request, response); }
重定向到Servlet_two结果又会是怎样呢？ 结果是如左边还是右边呢？
Filter_one前====> Filter_two前====> Filter_three前====> Servlet_one===> Servlet_two===> Filter_three后====> Filter_two后====> Filter_one后====>	Filter_one前====> Filter_two前====> Filter_three前====> Servlet_one===> Filter_one前====> Filter_two前====> Filter_three前====> Servlet_two===> Filter_three后====> Filter_two后====> Filter_one后====> Filter_three后====> Filter_two后====> Filter_one后====>

结果如上表（结果左）所示

这是为什么呢？过滤器不是对项目内所有文件都要进行过滤吗？为什么这里没有对Servlet_two进行过滤？原因就在这里<dispatcher>标签，内含四个参数：FORWARD、ERROR、INCLUDE、REQUEST；REQUEST为默认标签，并且一个<filter-mapping>内可以包含多个<dispatcher>标签；

修改Filter_one代码

  <filter-mapping>

    <filter-name>Filter_one</filter-name>

    <url-pattern>/*</url-pattern>

    <dispatcher>FORWARD</dispatcher>

    <dispatcher>REQUEST</dispatcher>

  </filter-mapping>

修改后结果如图所示

结果示意图

 

这样就可以在Servlet_one跳转到Servlet_two的时候，对Servlet_two也进行过滤。

ERROR参数又有什么作用呢？已知我们在程序调试的时候难免出现异常，或者url路径填写错误，那么网页就会提示这些错误

Error Status 500

Error Status 404

这样的错误提示信息较为相信，明眼人一眼就能看见错误信息，这样你的后台信息就会暴露出来，这样是非常不好。那么怎么替代这些错误信息呢？就要用到<dispatcher>标签中的ERROR参数。

修改Filter_one代码

在标签<filter-mapping>中添加子标签<dispatcher>并且参数为ERROR

<dispatcher>ERROR</dispatcher>

在标签<web-app>中添加子标签<error-page>

  <error-page>

  <!--状态码-->

  <error-code>404</error-code>

  <!--连接路径-->

  <location>/Test/WebContent/jsp/error_404_page.jsp</location>

  </error-page>

    <error-page>

  <error-code>500</error-code>

  <location>/Test/WebContent/jsp/error_500_page.jsp</location>

  </error-page>

当程序再出现异常的时候，就会跳转到我们自己设计的错误提示页面，不会将源代码错误信息显示在页面上。既美化又更加安全、健壮！

Error Status 500

Error Status 404