package me.gacl.web.filter;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
/**
* @ClassName: FilterDemo
* @Description:filter的三種典型應(yīng)用：
* 、可以在filter中根據(jù)條件決定是否調(diào)用chain.doFilter(request, response)方法，
* 即是否讓目標(biāo)資源執(zhí)行
* 、在讓目標(biāo)資源執(zhí)行之前，可以對(duì)request\response作預(yù)處理，再讓目標(biāo)資源執(zhí)行
* 、在目標(biāo)資源執(zhí)行之后，可以捕獲目標(biāo)資源的執(zhí)行結(jié)果，從而實(shí)現(xiàn)一些特殊的功能
* @author: 孤傲蒼狼
* @date: -- 下午::
*/ 
public class FilterDemo implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("----過濾器初始化----");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
//對(duì)request和response進(jìn)行一些預(yù)處理
request.setCharacterEncoding("UTF-");
response.setCharacterEncoding("UTF-");
response.setContentType("text/html;charset=UTF-");
System.out.println("FilterDemo執(zhí)行前?。?！");
chain.doFilter(request, response); //讓目標(biāo)資源執(zhí)行，放行
System.out.println("FilterDemo執(zhí)行后?。。?);
}
@Override
public void destroy() {
System.out.println("----過濾器銷毀----");
}
} 

<?xml version="." encoding="UTF-"?>
<web-app version="." 
xmlns="http://java.sun.com/xml/ns/javaee" 
xmlns:xsi="http://www.w.org//XMLSchema-instance" 
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
http://java.sun.com/xml/ns/javaee/web-app__.xsd">
<display-name></display-name> 
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<!--配置過濾器-->
<filter>
<filter-name>FilterDemo</filter-name>
<filter-class>me.gacl.web.filter.FilterDemo</filter-class>
</filter>
<!--映射過濾器-->
<filter-mapping>
<filter-name>FilterDemo</filter-name>
<!--“/*”表示攔截所有的請(qǐng)求 -->
<url-pattern>/*</url-pattern>
</filter-mapping>
</web-app> 

package me.gacl.web.filter;
import java.io.IOException;
import java.util.Enumeration;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
public class FilterDemo implements Filter {
/* 過濾器初始化
* @see javax.servlet.Filter#init(javax.servlet.FilterConfig)
*/
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("----過濾器初始化----");
/**
* <filter>
<filter-name>FilterDemo</filter-name>
<filter-class>me.gacl.web.filter.FilterDemo</filter-class>
<!--配置FilterDemo過濾器的初始化參數(shù)-->
<init-param>
<description>配置FilterDemo過濾器的初始化參數(shù)</description>
<param-name>name</param-name>
<param-value>gacl</param-value>
</init-param>
<init-param>
<description>配置FilterDemo過濾器的初始化參數(shù)</description>
<param-name>like</param-name>
<param-value>java</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>FilterDemo</filter-name>
<!--“/*”表示攔截所有的請(qǐng)求 -->
<url-pattern>/*</url-pattern>
</filter-mapping>
*/
//得到過濾器的名字
String filterName = filterConfig.getFilterName();
//得到在web.xml文件中配置的初始化參數(shù)
String initParam = filterConfig.getInitParameter("name");
String initParam = filterConfig.getInitParameter("like");
//返回過濾器的所有初始化參數(shù)的名字的枚舉集合。
Enumeration<String> initParameterNames = filterConfig.getInitParameterNames();
System.out.println(filterName);
System.out.println(initParam);
System.out.println(initParam);
while (initParameterNames.hasMoreElements()) {
String paramName = (String) initParameterNames.nextElement();
System.out.println(paramName);
}
}
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
System.out.println("FilterDemo執(zhí)行前?。?！");
chain.doFilter(request, response); //讓目標(biāo)資源執(zhí)行，放行
System.out.println("FilterDemo執(zhí)行后！?。?);
}
@Override
public void destroy() {
System.out.println("----過濾器銷毀----");
}
}

<filter>
<description>FilterDemo過濾器</description>
<filter-name>FilterDemo</filter-name>
<filter-class>me.gacl.web.filter.FilterDemo</filter-class>
<!--配置FilterDemo過濾器的初始化參數(shù)-->
<init-param>
<description>配置FilterDemo過濾器的初始化參數(shù)</description>
<param-name>name</param-name>
<param-value>gacl</param-value>
</init-param>
<init-param>
<description>配置FilterDemo過濾器的初始化參數(shù)</description>
<param-name>like</param-name>
<param-value>java</param-value>
</init-param>
</filter> 

<!--映射過濾器-->
<filter-mapping>
<filter-name>FilterDemo</filter-name>
<!--“/*”表示攔截所有的請(qǐng)求 -->
<url-pattern>/*</url-pattern>
</filter-mapping> 

<filter-mapping>
<filter-name>testFilter</filter-name>
<url-pattern>/index.jsp</url-pattern>
<dispatcher>REQUEST</dispatcher>
<dispatcher>FORWARD</dispatcher>
</filter-mapping>