Java Web学习笔记8

Posted 2020-08-24

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上下文参数(context-param)

由于init-param是配置在<servlet>标签里的,只能有这个Servlet来读取,因此它不是全局的参数,不能被其他的Servlet读取.

context-param叫做上下文参数,可以被所有的Sevlet读取.上下文标签使用<context-param>配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
    
  <context-param>
      <param-name>upload folder</param-name>
      <param-value>attachment</param-value>
  </context-param>
  
  <context-param>
      <param-name>allowed file type</param-name>
      <param-value>.gif, .jpg, .bmp</param-value>
  </context-param>

  <servlet>
    <servlet-name>ContextParamServlet</servlet-name>
    <servlet-class>com.helloxr.servlet.ContextParamServlet</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>ContextParamServlet</servlet-name>
    <url-pattern>/servlet/ContextParamServlet</url-pattern>
  </servlet-mapping>

package com.helloxr.servlet;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ContextParamServlet extends HttpServlet {

    private static final long serialVersionUID = 65464645464L;

    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        response.setCharacterEncoding("UTF-8");
        response.setContentType("text/html");
        
        PrintWriter out = response.getWriter();
        out.println("<!DOCTYPE HTML PUBLIC \\"-//W3C//DTD HTML 4.01 Transitional//EN\\">");
        out.println("<HTML>");
        out.println("  <HEAD><TITLE>读取上下文参数</TITLE></HEAD>");
        out.println("  <BODY>");
        out.println("  <link rel=‘stylesheet‘ type=‘text/css‘ href=‘../css/style.css‘>");
        out.println("<div align=center><br/>");
        out.println("<fieldset style=‘width:90%‘><legend>所有的上下文参数</legend><br/>");
        ServletContext servletContext = getServletConfig().getServletContext();
        
        String uploadFolder = servletContext.getInitParameter("upload folder");
        String allowedFileType = servletContext.getInitParameter("allowed file type");
            
        out.println("<div class=‘line‘>");
        out.println("   <div align=‘left‘ class=‘leftDiv‘>上传文件夹</div>");
        out.println("   <div align=‘left‘ class=‘rightDiv‘>" + uploadFolder + "</div>");
        out.println("</div>");
        out.println("<div class=‘line‘>");
        out.println("   <div align=‘left‘ class=‘leftDiv‘>实际磁盘路径</div>");
        out.println("   <div align=‘left‘ class=‘rightDiv‘>" + servletContext.getRealPath(uploadFolder) + "</div>");
        out.println("</div>");
        out.println("<div class=‘line‘>");
        out.println("   <div align=‘left‘ class=‘leftDiv‘>允许上传的文件类型</div>");
        out.println("   <div align=‘left‘ class=‘rightDiv‘>" + allowedFileType + "</div>");
        out.println("</div>");
        out.println("</fieldset></div>");
        out.println("  </BODY>");
        out.println("</HTML>");
        out.flush();
        out.close();
    }

}

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