J2EE学习经验：JSP学习总结2(转载)

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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