Servlet中的过滤器Filter用法

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Servlet中的过滤器Filter用法
1.过滤器的概念

Java中的Filter 并不是一个标准的Servlet ，它不能处理用户请求，也不能对客户端生成响应。主要用于对HttpServletRequest 进行预处理，也可以对HttpServletResponse 进行后处理，是个典型的处理链。

优点：过滤链的好处是，执行过程中任何时候都可以打断，只要不执行chain.doFilter()就不会再执行后面的过滤器和请求的内容。而在实际使用时，就要特别注意过滤链的执行顺序问题

2.过滤器的作用描述
- 在HttpServletRequest 到达Servlet 之前，拦截客户的HttpServletRequest 。
- 根据需要检查HttpServletRequest ，也可以修改HttpServletRequest 头和数据。
- 在HttpServletResponse 到达客户端之前，拦截HttpServletResponse 。
- 根据需要检查HttpServletResponse ，可以修改HttpServletResponse 头和数据。
3.过滤器的执行流程

4.Filter接口

1.如何驱动

在 web 应用程序启动时，web 服务器将根据 web.xml 文件中的配置信息来创建每个注册的 Filter 实例对象，并将其保存在服务器的内存中

2.方法介绍
5.FilterChain接口

1.如何实例化

代表当前 Filter 链的对象。由容器实现，容器将其实例作为参数传入过滤器对象的doFilter()方法中

2.作用

调用过滤器链中的下一个过滤器

filter实例：

web.xml配置
[html] view plain copy print?



 <filter>

 <filter-name>setCharacterEncoding</filter-name>

 <filter-class>com.company.strutstudy.web.servletstudy.filter.EncodingFilter</filter-class>

 <init-param>

 <param-name>encoding</param-name>

 <param-value>utf-8</param-value>

 </init-param>

 </filter>

 <filter-mapping>

 <filter-name>setCharacterEncoding</filter-name>

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

 </filter-mapping>





 <filter>

 <filter-name>logfilter</filter-name>

 <filter-class>com.company.strutstudy.web.servletstudy.filter.LogFilter</filter-class>

 </filter>

 <filter-mapping>

 <filter-name>logfilter</filter-name>

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

 </filter-mapping>
编码拦截器：
[java] view plain copy print?

public class EncodingFilter implements Filter {

 private String encoding;

 private Map<String, String> params = new HashMap<String, String>();

 // 项目结束时就已经进行销毁

 public void destroy() {

 System.out.println("end do the encoding filter!");

 params=null;

 encoding=null;

 }

 public void doFilter(ServletRequest req, ServletResponse resp,

 FilterChain chain) throws IOException, ServletException {

 //UtilTimerStack.push("EncodingFilter_doFilter:");

 System.out.println("before encoding " + encoding + " filter！");

 req.setCharacterEncoding(encoding);

 // resp.setCharacterEncoding(encoding);

 // resp.setContentType("text/html;charset="+encoding);

 chain.doFilter(req, resp);

 System.out.println("after encoding " + encoding + " filter！");

 System.err.println("----------------------------------------");

 //UtilTimerStack.pop("EncodingFilter_doFilter:");

 }



 // 项目启动时就已经进行读取

 public void init(FilterConfig config) throws ServletException {

 System.out.println("begin do the encoding filter!");

 encoding = config.getInitParameter("encoding");

 for (Enumeration e = config.getInitParameterNames(); e

 .hasMoreElements();) {

 String name = (String) e.nextElement();

 String value = config.getInitParameter(name);

 params.put(name, value);

 }

 }

}
日志拦截器：
[java] view plain copy print?

public class LogFilter implements Filter {

 FilterConfig config;



 public void destroy() {

 this.config = null;

 }



 public void doFilter(ServletRequest req, ServletResponse res,

 FilterChain chain) throws IOException, ServletException {

 // 获取ServletContext 对象，用于记录日志

 ServletContext context = this.config.getServletContext();

 //long before = System.currentTimeMillis();

 System.out.println("before the log filter!");

 //context.log("开始过滤");

 // 将请求转换成HttpServletRequest 请求

 HttpServletRequest hreq = (HttpServletRequest) req;

 // 记录日志

 System.out.println("Log Filter已经截获到用户的请求的地址:"+hreq.getServletPath() );

 //context.log("Filter已经截获到用户的请求的地址: " + hreq.getServletPath());

 try {

 // Filter 只是链式处理，请求依然转发到目的地址。

 chain.doFilter(req, res);

 } catch (Exception e) {

 e.printStackTrace();

 }

 System.out.println("after the log filter!");

 //long after = System.currentTimeMillis();

 // 记录日志

 //context.log("过滤结束");

 // 再次记录日志

 //context.log(" 请求被定位到" + ((HttpServletRequest) req).getRequestURI()

 // + "所花的时间为: " + (after - before));

 }



 public void init(FilterConfig config) throws ServletException {

 System.out.println("begin do the log filter!");

 this.config = config;

 }



}
HelloServlet类：
[java] view plain copy print?

public class HelloWorldServlet extends HttpServlet{



 /**

 * 查看httpservlet实现的service一看便知，起到了一个controll控制器的作用(转向的)

 * 之后便是跳转至我们熟悉的doget,dopost等方法中

 */

 @Override

 protected void service(HttpServletRequest req, HttpServletResponse resp)

 throws ServletException, IOException {

 System.out.println("doservice..."+this.getInitParameter("encoding"));



 super.service(req, resp);

 }



 @Override

 protected void doGet(HttpServletRequest req, HttpServletResponse resp)

 throws ServletException, IOException {

 System.out.println("doget...");

 doPost(req, resp);

 }



 @Override

 protected void doPost(HttpServletRequest req, HttpServletResponse resp)

 throws ServletException, IOException {

 System.out.println("dopost...");

 }







}
结果：
[plain] view plain copy print?

before encoding utf-8 filter！

 before the log filter!

 Log Filter已经截获到用户的请求的地址:/hello

 doservice...UTF-8

 doget...

 dopost...

 after the log filter!

 after encoding utf-8 filter！

 ----------------------------------------
总结：

1.过滤器执行流程

2.常用过滤器

转载自http://blog.csdn.net/techbirds_bao/article/details/8243800

<div id="article_content" class="article_content">

1.过滤器的概念
<a href="http://lib.csdn.net/base/javaee" class="replace_word" title="Java EE知识库" target="_blank" style="color:#df3434; font-weight:bold;">Java</a>中的Filter 并不是一个标准的Servlet ，它不能处理用户请求，也不能对客户端生成响应。主要用于对HttpServletRequest 进行预处理，也可以对HttpServletResponse 进行后处理，是个典型的处理链。 

优点：过滤链的好处是，执行过程中任何时候都可以打断，只要不执行chain.doFilter()就不会再执行后面的过滤器和请求的内容。而在实际使用时，就要特别注意过滤链的执行顺序问题
2.过滤器的作用描述

<ul>
<li>在HttpServletRequest 到达Servlet 之前，拦截客户的HttpServletRequest 。 </li><li>  根据需要检查HttpServletRequest ，也可以修改HttpServletRequest 头和数据。 </li><li>  在HttpServletResponse 到达客户端之前，拦截HttpServletResponse 。 </li><li>根据需要检查HttpServletResponse ，可以修改HttpServletResponse 头和数据。</li></ul>

3.过滤器的执行流程
<img src="http://img.my.csdn.net/uploads/201211/30/1354261672_8450.jpg" alt=""><img src="http://img.my.csdn.net/uploads/201211/30/1354261343_9300.png" alt="" style="white-space:pre; text-align:left">
 

4.Filter接口
<blockquote style="margin:0 0 0 40px; border:none; padding:0px">
1.如何驱动
</blockquote>

<blockquote style="margin:0 0 0 40px; border:none; padding:0px">
<blockquote style="margin:0 0 0 40px; border:none; padding:0px">
在 web 应用程序启动时，web 服务器将根据 web.xml 文件中的配置信息来创建每个注册的 Filter 实例对象，并将其保存在服务器的内存中
</blockquote>
</blockquote>

<blockquote style="margin:0 0 0 40px; border:none; padding:0px">
2.方法介绍
</blockquote>


<ul>
<ul>
<li>init()  Init 方法在 Filter 生命周期中仅执行一次，web 容器在调用 init 方法时</li><li>destory()  在Web容器卸载 Filter 对象之前被调用。该方法在Filter的生命周期中仅执行一次。在这个方法中，可以释放过滤器使用的资源。</li><li>doFilter() Filter 链的执行 </li></ul>
</ul>

5.FilterChain接口
<blockquote style="margin:0 0 0 40px; border:none; padding:0px">
1.如何实例化
</blockquote>

<blockquote style="margin:0 0 0 40px; border:none; padding:0px">
<blockquote style="margin:0 0 0 40px; border:none; padding:0px">
代表当前 Filter 链的对象。由容器实现，容器将其实例作为参数传入过滤器对象的doFilter()方法中
</blockquote>
</blockquote>
<blockquote style="margin:0 0 0 40px; border:none; padding:0px">
2.作用
</blockquote>

<blockquote style="margin:0 0 0 40px; border:none; padding:0px">
<blockquote style="margin:0 0 0 40px; border:none; padding:0px">
调用过滤器链中的下一个过滤器
</blockquote>
</blockquote>
filter实例：
web.xml配置

<div class="dp-highlighter bg_html"><div class="bar"><div class="tools">[html] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;">copy</a><div style="position: absolute; left: 463px; top: 1519px; 24px; height: 13px; z-index: 99;"><embed id="ZeroClipboardMovie_1" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" name="ZeroClipboardMovie_1" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=1&width=24&height=13" wmode="transparent" width="24" align="middle" height="13"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;">?</a></div></div><ol start="1" class="dp-xml"><li class="alt">  </li><li class="">    <filter>  </li><li class="alt">        <filter-name>setCharacterEncoding</filter-name>  </li><li class="">        <filter-class>com.company.strutstudy.web.servletstudy.filter.EncodingFilter</filter-class>  </li><li class="alt">        <init-param>  </li><li class="">            <param-name>encoding</param-name>  </li><li class="alt">            <param-value>utf-8</param-value>  </li><li class="">        </init-param>  </li><li class="alt">    </filter>  </li><li class="">    <filter-mapping>  </li><li class="alt">        <filter-name>setCharacterEncoding</filter-name>  </li><li class="">        <url-pattern>/*</url-pattern>  </li><li class="alt">    </filter-mapping>  </li><li class="">   </li><li class="alt">  </li><li class="">    <filter>  </li><li class="alt">        <filter-name>logfilter</filter-name>  </li><li class="">        <filter-class>com.company.strutstudy.web.servletstudy.filter.LogFilter</filter-class>  </li><li class="alt">    </filter>  </li><li class="">    <filter-mapping>  </li><li class="alt">        <filter-name>logfilter</filter-name>  </li><li class="">        <url-pattern>/*</url-pattern>  </li><li class="alt">    </filter-mapping>  </li></ol><div class="save_code tracking-ad" data-mod="popu_249" style="display: none;"><a href="javascript:;" target="_blank"><img src="http://static.blog.csdn.net/images/save_snippets.png"></a></div></div><pre name="code" class="html" style="display: none;">
 <filter>
 <filter-name>setCharacterEncoding</filter-name>
 <filter-class>com.company.strutstudy.web.servletstudy.filter.EncodingFilter</filter-class>
 <init-param>
 <param-name>encoding</param-name>
 <param-value>utf-8</param-value>
 </init-param>
 </filter>
 <filter-mapping>
 <filter-name>setCharacterEncoding</filter-name>
 <url-pattern>/*</url-pattern>
 </filter-mapping>


 <filter>
 <filter-name>logfilter</filter-name>
 <filter-class>com.company.strutstudy.web.servletstudy.filter.LogFilter</filter-class>
 </filter>
 <filter-mapping>
 <filter-name>logfilter</filter-name>
 <url-pattern>/*</url-pattern>
 </filter-mapping></pre> 
编码拦截器：


<div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;">copy</a><div style="position: absolute; left: 462px; top: 2049px; 24px; height: 13px; z-index: 99;"><embed id="ZeroClipboardMovie_2" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" name="ZeroClipboardMovie_2" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=2&width=24&height=13" wmode="transparent" width="24" align="middle" height="13"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public class EncodingFilter implements Filter {  </li><li class="">    private String encoding;  </li><li class="alt">    private Map<String, String> params = new HashMap<String, String>();  </li><li class="">    // 项目结束时就已经进行销毁  </li><li class="alt">    public void destroy() {  </li><li class="">        System.out.println("end do the encoding filter!");  </li><li class="alt">        params=null;  </li><li class="">        encoding=null;  </li><li class="alt">    }  </li><li class="">    public void doFilter(ServletRequest req, ServletResponse resp,  </li><li class="alt">            FilterChain chain) throws IOException, ServletException {  </li><li class="">        //UtilTimerStack.push("EncodingFilter_doFilter:");  </li><li class="alt">        System.out.println("before encoding " + encoding + " filter！");  </li><li class="">        req.setCharacterEncoding(encoding);  </li><li class="alt">        // resp.setCharacterEncoding(encoding);  </li><li class="">        // resp.setContentType("text/html;charset="+encoding);  </li><li class="alt">        chain.doFilter(req, resp);        </li><li class="">        System.out.println("after encoding " + encoding + " filter！");  </li><li class="alt">        System.err.println("----------------------------------------");  </li><li class="">        //UtilTimerStack.pop("EncodingFilter_doFilter:");  </li><li class="alt">    }  </li><li class="">   </li><li class="alt">    // 项目启动时就已经进行读取  </li><li class="">    public void init(FilterConfig config) throws ServletException {  </li><li class="alt">        System.out.println("begin do the encoding filter!");  </li><li class="">        encoding = config.getInitParameter("encoding");  </li><li class="alt">        for (Enumeration e = config.getInitParameterNames(); e  </li><li class="">                .hasMoreElements();) {  </li><li class="alt">            String name = (String) e.nextElement();  </li><li class="">            String value = config.getInitParameter(name);  </li><li class="alt">            params.put(name, value);  </li><li class="">        }  </li><li class="alt">    }  </li><li class=""> }  </li></ol><div class="save_code tracking-ad" data-mod="popu_249" style="display: none;"><a href="javascript:;" target="_blank"><img src="http://static.blog.csdn.net/images/save_snippets.png"></a></div></div><pre name="code" class="java" style="display: none;">public class EncodingFilter implements Filter {
 private String encoding;
 private Map<String, String> params = new HashMap<String, String>();
 // 项目结束时就已经进行销毁
 public void destroy() {
 System.out.println("end do the encoding filter!");
 params=null;
 encoding=null;
 }
 public void doFilter(ServletRequest req, ServletResponse resp,
 FilterChain chain) throws IOException, ServletException {
 //UtilTimerStack.push("EncodingFilter_doFilter:");
 System.out.println("before encoding " + encoding + " filter！");
 req.setCharacterEncoding(encoding);
 // resp.setCharacterEncoding(encoding);
 // resp.setContentType("text/html;charset="+encoding);
 chain.doFilter(req, resp);
 System.out.println("after encoding " + encoding + " filter！");
 System.err.println("----------------------------------------");
 //UtilTimerStack.pop("EncodingFilter_doFilter:");
 }

 // 项目启动时就已经进行读取
 public void init(FilterConfig config) throws ServletException {
 System.out.println("begin do the encoding filter!");
 encoding = config.getInitParameter("encoding");
 for (Enumeration e = config.getInitParameterNames(); e
 .hasMoreElements();) {
 String name = (String) e.nextElement();
 String value = config.getInitParameter(name);
 params.put(name, value);
 }
 }
}</pre>日志拦截器：<div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;">copy</a><div style="position: absolute; left: 462px; top: 2751px; 24px; height: 13px; z-index: 99;"><embed id="ZeroClipboardMovie_3" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" name="ZeroClipboardMovie_3" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=3&width=24&height=13" wmode="transparent" width="24" align="middle" height="13"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public class LogFilter implements Filter {  </li><li class="">    FilterConfig config;  </li><li class="alt">   </li><li class="">    public void destroy() {  </li><li class="alt">        this.config = null;  </li><li class="">    }  </li><li class="alt">   </li><li class="">    public void doFilter(ServletRequest req, ServletResponse res,  </li><li class="alt">            FilterChain chain) throws IOException, ServletException {  </li><li class="">        // 获取ServletContext 对象，用于记录日志  </li><li class="alt">        ServletContext context = this.config.getServletContext();  </li><li class="">        //long before = System.currentTimeMillis();  </li><li class="alt">        System.out.println("before the log filter!");  </li><li class="">        //context.log("开始过滤");  </li><li class="alt">        // 将请求转换成HttpServletRequest 请求  </li><li class="">        HttpServletRequest hreq = (HttpServletRequest) req;  </li><li class="alt">        // 记录日志  </li><li class="">        System.out.println("Log Filter已经截获到用户的请求的地址:"+hreq.getServletPath() );  </li><li class="alt">        //context.log("Filter已经截获到用户的请求的地址: " + hreq.getServletPath());  </li><li class="">        try {  </li><li class="alt">            // Filter 只是链式处理，请求依然转发到目的地址。  </li><li class="">            chain.doFilter(req, res);  </li><li class="alt">        } catch (Exception e) {  </li><li class="">            e.printStackTrace();  </li><li class="alt">        }  </li><li class="">        System.out.println("after the log filter!");  </li><li class="alt">        //long after = System.currentTimeMillis();  </li><li class="">        // 记录日志  </li><li class="alt">        //context.log("过滤结束");  </li><li class="">        // 再次记录日志  </li><li class="alt">        //context.log(" 请求被定位到" + ((HttpServletRequest) req).getRequestURI()  </li><li class="">        //      + "所花的时间为: " + (after - before));  </li><li class="alt">    }  </li><li class="">   </li><li class="alt">    public void init(FilterConfig config) throws ServletException {  </li><li class="">        System.out.println("begin do the log filter!");  </li><li class="alt">        this.config = config;  </li><li class="">    }  </li><li class="alt">   </li><li class=""> }  </li></ol><div class="save_code tracking-ad" data-mod="popu_249" style="display: none;"><a href="javascript:;" target="_blank"><img src="http://static.blog.csdn.net/images/save_snippets.png"></a></div></div><pre name="code" class="java" style="display: none;">public class LogFilter implements Filter {
 FilterConfig config;

 public void destroy() {
 this.config = null;
 }

 public void doFilter(ServletRequest req, ServletResponse res,
 FilterChain chain) throws IOException, ServletException {
 // 获取ServletContext 对象，用于记录日志
 ServletContext context = this.config.getServletContext();
 //long before = System.currentTimeMillis();
 System.out.println("before the log filter!");
 //context.log("开始过滤");
 // 将请求转换成HttpServletRequest 请求
 HttpServletRequest hreq = (HttpServletRequest) req;
 // 记录日志
 System.out.println("Log Filter已经截获到用户的请求的地址:"+hreq.getServletPath() );
 //context.log("Filter已经截获到用户的请求的地址: " + hreq.getServletPath());
 try {
 // Filter 只是链式处理，请求依然转发到目的地址。
 chain.doFilter(req, res);
 } catch (Exception e) {
 e.printStackTrace();
 }
 System.out.println("after the log filter!");
 //long after = System.currentTimeMillis();
 // 记录日志
 //context.log("过滤结束");
 // 再次记录日志
 //context.log(" 请求被定位到" + ((HttpServletRequest) req).getRequestURI()
 // + "所花的时间为: " + (after - before));
 }

 public void init(FilterConfig config) throws ServletException {
 System.out.println("begin do the log filter!");
 this.config = config;
 }

}</pre>HelloServlet类：<div class="dp-highlighter bg_java"><div class="bar"><div class="tools">[java] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;">copy</a><div style="position: absolute; left: 462px; top: 3561px; 24px; height: 13px; z-index: 99;"><embed id="ZeroClipboardMovie_4" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" name="ZeroClipboardMovie_4" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=4&width=24&height=13" wmode="transparent" width="24" align="middle" height="13"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;">?</a></div></div><ol start="1" class="dp-j"><li class="alt">public class HelloWorldServlet extends HttpServlet{  </li><li class="">   </li><li class="alt">    /** </li><li class="">     * 查看httpservlet实现的service一看便知，起到了一个controll控制器的作用(转向的) </li><li class="alt">     * 之后便是跳转至我们熟悉的doget,dopost等方法中  </li><li class="">     */  </li><li class="alt">    @Override  </li><li class="">    protected void service(HttpServletRequest req, HttpServletResponse resp)  </li><li class="alt">            throws ServletException, IOException {  </li><li class="">        System.out.println("doservice..."+this.getInitParameter("encoding"));  </li><li class="alt">          </li><li class="">        super.service(req, resp);  </li><li class="alt">    }  </li><li class="">   </li><li class="alt">    @Override  </li><li class="">    protected void doGet(HttpServletRequest req, HttpServletResponse resp)  </li><li class="alt">            throws ServletException, IOException {  </li><li class="">        System.out.println("doget...");  </li><li class="alt">        doPost(req, resp);  </li><li class="">    }  </li><li class="alt">   </li><li class="">    @Override  </li><li class="alt">    protected void doPost(HttpServletRequest req, HttpServletResponse resp)  </li><li class="">            throws ServletException, IOException {  </li><li class="alt">        System.out.println("dopost...");  </li><li class="">    }  </li><li class="alt">      </li><li class="">      </li><li class="alt">   </li><li class=""> }  </li></ol><div class="save_code tracking-ad" data-mod="popu_249" style="display: none;"><a href="javascript:;" target="_blank"><img src="http://static.blog.csdn.net/images/save_snippets.png"></a></div></div><pre name="code" class="java" style="display: none;">public class HelloWorldServlet extends HttpServlet{

 /**
 * 查看httpservlet实现的service一看便知，起到了一个controll控制器的作用(转向的)
 * 之后便是跳转至我们熟悉的doget,dopost等方法中
 */
 @Override
 protected void service(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException {
 System.out.println("doservice..."+this.getInitParameter("encoding"));

 super.service(req, resp);
 }

 @Override
 protected void doGet(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException {
 System.out.println("doget...");
 doPost(req, resp);
 }

 @Override
 protected void doPost(HttpServletRequest req, HttpServletResponse resp)
 throws ServletException, IOException {
 System.out.println("dopost...");
 }



}</pre>结果： 
<div class="dp-highlighter bg_plain"><div class="bar"><div class="tools">[plain] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;">copy</a><div style="position: absolute; left: 464px; top: 4191px; 24px; height: 13px; z-index: 99;"><embed id="ZeroClipboardMovie_5" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" name="ZeroClipboardMovie_5" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=5&width=24&height=13" wmode="transparent" width="24" align="middle" height="13"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;">?</a></div></div><ol start="1"><li class="alt">before encoding utf-8 filter！  </li><li class="">  before the log filter!  </li><li class="alt">  Log Filter已经截获到用户的请求的地址:/hello  </li><li class="">  doservice...UTF-8  </li><li class="alt">  doget...  </li><li class="">  dopost...  </li><li class="alt">  after the log filter!  </li><li class="">  after encoding utf-8 filter！  </li><li class="alt">  ----------------------------------------  </li></ol><div class="save_code tracking-ad" data-mod="popu_249" style="display: none;"><a href="javascript:;" target="_blank"><img src="http://static.blog.csdn.net/images/save_snippets.png"></a></div></div><pre name="code" class="plain" style="display: none;">before encoding utf-8 filter！
before the log filter!
Log Filter已经截获到用户的请求的地址:/hello
doservice...UTF-8
doget...
dopost...
after the log filter!
after encoding utf-8 filter！
----------------------------------------</pre>
总结：
<blockquote style="margin:0 0 0 40px; border:none; padding:0px">
1.过滤器执行流程
2.常用过滤器
</blockquote>
<div class="dp-highlighter bg_html"><div class="bar"><div class="tools">[html] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;">copy</a><div style="position: absolute; left: 463px; top: 4495px; 24px; height: 13px; z-index: 99;"><embed id="ZeroClipboardMovie_6" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" name="ZeroClipboardMovie_6" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=6&width=24&height=13" wmode="transparent" width="24" align="middle" height="13"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;">?</a></div></div><ol start="1" class="dp-xml"><li class="alt"><pre name="code" class="plain"><pre></pre><pre name="code" class="plain"></pre><pre></pre>  </li><li class=""><pre></pre>  </li><li class="alt"><pre></pre>  </li><li class=""><pre></pre>  </li><li class="alt"><pre></pre>  </li><li class=""><pre></pre>  </li><li class="alt"><pre></pre>  </li><li class="">     </li><li class="alt"></pre>  </li></ol><div class="save_code tracking-ad" data-mod="popu_249" style="display: none;"><a href="javascript:;" target="_blank"><img src="http://static.blog.csdn.net/images/save_snippets.png"></a></div></div><pre name="code" class="html" style="display: none;"><div class="dp-highlighter bg_plain"><div class="bar"><div class="tools">[plain] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;">copy</a><div style="position: absolute; left: 0px; top: 0px; 0px; height: 0px; z-index: 99;"><embed id="ZeroClipboardMovie_7" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" name="ZeroClipboardMovie_7" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=7&width=0&height=0" wmode="transparent" width="0" align="middle" height="0"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;">?</a></div></div><ol start="1"><li class="alt"><pre></pre><pre name="code" class="plain"></pre><pre></pre>  </li><li class=""><pre></pre>  </li><li class="alt"><pre></pre>  </li><li class=""><pre></pre>  </li><li class="alt"><pre></pre>  </li><li class=""><pre></pre>  </li><li class="alt"><pre></pre>  </li><li class="">     </li></ol><div class="save_code tracking-ad" data-mod="popu_249"><a href="javascript:;" target="_blank"><img src="http://static.blog.csdn.net/images/save_snippets.png"></a></div></div><pre name="code" class="plain" style="display: none;"><pre></pre><div class="dp-highlighter bg_plain"><div class="bar"><div class="tools">[plain] <a href="#" class="ViewSource" title="view plain" onclick="dp.sh.Toolbar.Command('ViewSource',this);return false;">view plain</a> <a href="#" class="CopyToClipboard" title="copy" onclick="dp.sh.Toolbar.Command('CopyToClipboard',this);return false;">copy</a><div style="position: absolute; left: 0px; top: 0px; 0px; height: 0px; z-index: 99;"><embed id="ZeroClipboardMovie_8" src="http://static.blog.csdn.net/scripts/ZeroClipboard/ZeroClipboard.swf" loop="false" menu="false" quality="best" bgcolor="#ffffff" name="ZeroClipboardMovie_8" allowscriptaccess="always" allowfullscreen="false" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" flashvars="id=8&width=0&height=0" wmode="transparent" width="0" align="middle" height="0"></div> <a href="#" class="PrintSource" title="print" onclick="dp.sh.Toolbar.Command('PrintSource',this);return false;">print</a><a href="#" class="About" title="?" onclick="dp.sh.Toolbar.Command('About',this);return false;">?</a></div></div><ol start="1"><li class="alt">  </li></ol><div class="save_code tracking-ad" data-mod="popu_249"><a href="javascript:;" target="_blank"><img src="http://static.blog.csdn.net/images/save_snippets.png"></a></div></div><pre name="code" class="plain" style="display: none;"></pre><pre></pre>
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原文地址：https://www.cnblogs.com/tiancai/p/6040004.html