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摘要: 用Servlet开发和配置过滤器(字符集设置)
下面我们来看一个具体的例子,这个例子将介绍怎么开发过滤器,并且介绍怎么在web.xml文件里配置过滤器。这个例子里有两个JSP页面,前一个页面用户输入一些信息然后提交,后一个页面显示用户提交的信息。在提交信息后,要经过两个过滤器的处理,一个检查用户是否登录,一个把用户的提交信息用GB2312进行重新编码。
开发一个Filter,这个Filter需要实现Filter接口,Filter接口定义了以下的方法:
</td> </tr> </table>destroy() //由Web容器调用,销毁此Filter
init(FilterConfig filterConfig) ///由Web容器调用,初始化此Filter
doFilter(ServletRequest request, ServletResponse response,
FilterChain chain)//具体过滤处理代码
</td> </tr> </table>1 // ==================== Program Discription =====================
2 // 程序名称:示例14-7 : EncodingFilter .java
3 // 程序目的:学习使用编码过滤器
4 // ==============================================================
5 import javax.servlet.FilterChain;
6 import javax.servlet.ServletRequest;
7 import javax.servlet.ServletResponse;
8 import java.io.IOException;
9 import javax.servlet.Filter;
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse;
12 import javax.servlet.ServletException;
13 import javax.servlet.FilterConfig;
14
15 public class EncodingFilter implements Filter
16 {
17
18 private String targetEncoding = "gb2312";
19 protected FilterConfig filterConfig;
20
21 public void init(FilterConfig config) throws ServletException {
22 this.filterConfig = config;
23 this.targetEncoding = config.getInitParameter("encoding");
24 }
25
26
27 public void doFilter(ServletRequest srequest,
ServletResponse sresponse,FilterChain chain)
28 throws IOException, ServletException {
29
30 HttpServletRequest request = (HttpServletRequest)srequest;
31 request.setCharacterEncoding(targetEncoding);//把请求用指定的方式编码
32 // 把处理发送到下一个过滤器
33 chain.doFilter(srequest,sresponse);
34 }
35
36 public void destroy()
37 {
38 this.filterConfig=null;
39 }
40
41 public void setFilterConfig(final FilterConfig filterConfig)
42 {
43 this.filterConfig=filterConfig;
44 }
45 }
</td> </tr> </table>1 // ==================== Program Discription =====================
2 // 程序名称:示例14-8 : LoginFilter.java
3 // 程序目的:学习使用登录过滤器
4 // ==============================================================
5 import javax.servlet.FilterChain;
6 import javax.servlet.ServletRequest;
7 import javax.servlet.ServletResponse;
8 import java.io.IOException;
9 import javax.servlet.Filter;
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse;
12 import javax.servlet.ServletException;
13 import javax.servlet.FilterConfig;
14
15 public class LoginFilter implements Filter
16 {
17 String LOGIN_PAGE="init.jsp";
18 protected FilterConfig filterConfig;
19 public void doFilter(final ServletRequest req,final ServletResponse
res,FilterChain chain)throws IOException,ServletException
20 {
21 HttpServletRequest hreq = (HttpServletRequest)req;
22 HttpServletResponse hres = (HttpServletResponse)res;
23 String isLog=(String)hreq.getSession().getAttribute("isLog");
24 if((isLog!=null)&&((isLog.equals("true"))||(isLog=="true")))//检查是否登录
25 {
26 chain.doFilter(req,res);
27 return ;
28 }
29 else
30 hres.sendRedirect(LOGIN_PAGE);//如果没有登录,把视图派发到登录页面
31 }
32
33 public void destroy()
34 {
35 this.filterConfig=null;
36 }
37 public void init(FilterConfig config)
38 {
39 this.filterConfig=config;
40 }
41 public void setFilterConfig(final FilterConfig filterConfig)
42 {
43 this.filterConfig=filterConfig;
44 }
45 }
</td> </tr> </table>
encoding
EncodingFilter
encoding
gb2312
auth
LoginFilter
encoding
/*
auth
/target.jsp
</td> </tr> </table><% session.setAttribute("isLog","true");%>
</td> </tr> </table>
encoding
/*
</td> </tr> </table>
encoding
/nothing
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