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

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
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。
doFilter() Filter 链的执行

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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