Filter应用+struts2x拦截器区别

(1)
Filter与struts2x拦截器区别：
Filter：
当程序请求servlet,jsp时，Filter会进行拦截。程序将先经过filter后，才到达目标的servlet,jsp；常用于系统权限管理（即用户访问某些页面之前，进行Filter权限检查）
struts2x拦截器：
只是在程序访问Action之前进行拦截。常用于记录系统操作日志，或添加额外功能。

(2)
Filter简介：
Filter的三个方法:init(),destroy(),doFilter();

三个实例如下：
(1)-------<利用filter进行中文字符处理>------------
1)
在web.xml中的配置:
<filter>
<filter-name>encoding</filter-name>
<filter-class>
org.lxh.myzngt.filter.EncodingFilter
</filter-class>
<init-param>
<param-name>charset</param-name>
<param-value>gbk</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>encoding</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
2)
JAVA代码:
public class EncodingFilter implements Filter {
private String charset = null;
public void destroy() {
}
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
req.setCharacterEncoding(this.charset);
chain.doFilter(req, resp);
}
//Filter获取web.xml中的初始参数;
public void init(FilterConfig arg0) throws ServletException {
this.charset = arg0.getInitParameter("charset");
}
}

(2)<利用filter进行用户登录过滤>------------
1)
<filter>
<filter-name>userlogin</filter-name>
<filter-class>
org.lxh.myzngt.filter.UserLoginFilter
</filter-class>
</filter>
<filter-mapping>
<filter-name>userlogin</filter-name>
<url-pattern>/jsp/user/*</url-pattern>
</filter-mapping>
<filter-mapping> -->可以多个匹配!!!!
<filter-name>userlogin</filter-name>
<url-pattern>/jsp/ques/*</url-pattern>
</filter-mapping>
2)
public class UserLoginFilter implements Filter {
public void destroy() {
}
public void doFilter(ServletRequest arg0, ServletResponse arg1,
FilterChain arg2) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) arg0;
if (req.getSession().getAttribute("userid") != null) {
arg2.doFilter(arg0, arg1);
} else {
req.getRequestDispatcher("forward.htm").forward(arg0, arg1) ;
}
}
public void init(FilterConfig arg0) throws ServletException {
}
}

（3）
在用户访问目标页面之前，利用Filter进行进行权限查询：
1.用户是否已登录（即session中是否有相应的记录）
2.用户权限是否符合访问页面要求。
如下：
(1)在web.xml中添加：
<filter>
<filter-name>PrivilegeFilter</filter-name>
<filter-class>com.demo.web.filter.PrivilegeFilter</filter-class>
<init-param>
<param-name>doNotFilterURL</param-name>
<param-value>
admin/rand, /login, admin/logout, /common/, /images/, /style/, /js/,
/fckeditor/, /userFilesAbsolutePath, /editPass
</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>PrivilegeFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

(2)
com.demo.web.filter.PrivilegeFilter定义：
public class PrivilegeFilter implements Filter {
/** 不需要过滤的URL */
private String[] doNotFilterURL;
public void init(FilterConfig filterConfig) throws ServletException {
String params = filterConfig.getInitParameter("doNotFilterURL");
if (params != null) {
String urls[] = params.split(",");
doNotFilterURL = new String[urls.length];
for (int i = 0, size = urls.length; i < size; i++) {
doNotFilterURL[i] = urls[i];
}
}
}

HttpServletRequest req = (HttpServletRequest) request;
String requestPath = req.getRequestURI(); //如：demo/login.action
String contextRoot = req.getContextPath(); //如：demo
int length = contextRoot.length();
String path = requestPath.substring(length); //如：/login.action
if (path != null && path.length() != 0) {
path = path.trim();
}
/** 登录页面不进行拦截 */
if (Constants.FIRST_LOGIN_URL.getStringValue().equals(path)) {
return true;
}

//获取请求的地址，比对不需要过滤的URL的数组doNotFilterURL。
boolean doNotFilter = false;
if (doNotFilterURL != null) {
for (String url : doNotFilterURL) {
if (url != null && path.contains(url.trim())) {
doNotFilter = true;
break;
}
}
}
//对不属于不用过滤的，查询数据表，看用户是否有权访问。若没，则返回提示用户无限访问页面。若有，则直接通过。
}
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