J2EE学习经验：JSP学习总结2

接着写个Servlet来加载log4j：

package powerwind.servlet;

import org.apache.log4j.Logger;
import org.apache.log4j.PropertyConfigurator;

import javax.servlet. * ;
import javax.servlet.http. * ;

public class Log4jInit extends HttpServlet {
public void init(ServletConfig config) throws ServletException {
         super .init(config);
          String prefix = getServletContext().getRealPath( " / " );
          String file = getInitParameter( " log4j " );
          System.out.println( " init log4j... " );
         if (file != null ){
            PropertyConfigurator.configure(prefix + file);
          } else
          {
                   PropertyConfigurator.configure(prefix + " log4j.properties " );
          }
}
}

然后同时要在web.xml下配置：

< servlet >
          < servlet-name > log4jInit </ servlet-name >
          < servlet-class > powerwind.servlet.Log4jInit </ servlet-class >
               < init-param >
                 < param-name > log4j </ param-name >
                 < param-value > WEB-INF/classes/log4j.properties </ param-value >
               </ init-param >
          < load-on-startup > 1 </ load-on-startup >
</ servlet >

6、国际化

# test_zh_CN.properties
#login page
login.title = 登录页面

小型的应用中，我们并不常需要国际化。但是，如果网站要中文版和英文版的话，这个就不错啦。使用时很简单，把资源 test_zh_CN.properties文件放到classes目录下，然后用JSTL的fmt标签调用。

< fmt:setLocale value ="zh_CN"     scope =”session” />
< fmt:setBundle basename ="test" scope =”session” var =”hehe” />
< fmt:message key ="login.title" bundle =”${hehe}” scope =”session” />

其中var和scope属性不是必需的。三者结合，就可以实现国际化了。

二、极限与安全

资源放在WEB-INF下是安全的，因为这个目录对于客户端是不存在的。权限控制并不是仅仅这样就可以了。如果只是简单地判断用户是否登录，可用一个过滤器检查Session对象即可。若需要级别控制的话，就在Session中保存级别信息，然后加以判断。

一般把权限的控制做成一个标签（tag）。如：

public int doEndTag() throws JspException {
                HttpSession session = pageContext.getSession();
               if ((session != null ) && (session.getAttribute( " user " ) != null )) {
                       String t = ((UserBean) session.getAttribute( " user " )).getType();
                      if (t == null || role == null ) {
                              invalid();
                             return (SKIP_PAGE);
                       }
                       String[] roles = role.split(delimiter);
                      for ( int i = 0 ; i < roles.length; i ++ ) {
                             if (roles[i].equalsIgnoreCase(role))
                                    return (EVAL_PAGE);
                       }
                } else {
                       invalid();
                      return (SKIP_PAGE);
                }
               return (EVAL_PAGE);
         }

三、上传与下载

上传的话，一般使用已有的组件，如commons-fileupload 或者欧莱礼的cos （可能会遇到中文编码的问题）。而下载，比较简单，就自己写了个Servlet。

public void handleRequest(HttpServletRequest request,
                HttpServletResponse response) throws IOException, ServletException {
                String name = request.getParameter( " name " );
                String type = request.getParameter( " type " );
                String dir = request.getParameter( " dir " );
               if (name == null || name.length() < 2 || dir == null || dir.length() < 1 || type == null || type.length() < 1 ) {
                      throw new ServletException( " Sorry,error occured " );
                }
               char ch = dir.charAt(dir.length() - 1 );
               if (ch != ' / ' || ch != ' \ ' )
                       dir = dir + " / " ;
                ServletOutputStream os = null ;
                BufferedInputStream bis = null ;
               try {
                       File file = new File(dir + name);
                      if ( ! file.exists() || file.length() >= Integer.MAX_VALUE) {
                              logger.error( " Invalid file or file to large,file: " + name);
                             throw new ServletException(
                                           " Invalid file or file to large,file: " + name);
                       }
                       response.setContentType( " application/ " + type);
                       response.addHeader( " Content-Disposition " , " attachment; filename= " + name);
                       response.setContentLength(( int ) file.length());
                       os = response.getOutputStream();
                       bis = new BufferedInputStream( new FileInputStream(file));
                      int size = - 1 ;
                      while ((size = bis.read()) != - 1 )
                              os.write(size);
                } catch (IOException ioe) {
                      throw new ServletException(ioe.getMessage());
                } finally {
                      if (os != null )
                              os.close();
                      if (bis != null )
                              bis.close();
                }
         }

          以上只是个示例程序，灵活与方便的做法应该是在Servlet初始化参数（<init-param>）设置下载文件所在目录，当然也可以在页面中设置参数。甚至可以做成一个下载标签，方便使用。

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