Tomcat中使用servletContext
Tomcat中使用servletContext
- 运行在JVM上的每一个web应用程序都有一个与之对应的Servlet上下文（Servlet运行环境）
- Servlet API提供ServletContext接口用来标识Servlet上下文，ServletContext对象可以被web应用程序中的所有Servlet访问
- ServletContext对象是web服务器中的一个一直路径的根
- ServletContext用来解决不同用户之间的数据共享
ServletContext的特点
- 由服务器创建
- 所有用户共享同一个ServletContext对象
- 所有的Servlet都可以访问到同一个ServletContext中的属性
- 每一个web项目对象的是一个ServletContext
ServletContext的使用
-
获取ServletContext
- 方式1
ServletContext servletContext = this.getServletContext() - 方式2
ServletContext servletContext1 = this.getServletConfig().getServletContext(); - 方式3
ServletContext servletContext2 = request.getSession().getServletContext();
- 方式1
-
servletcontext设置属性值
servletContext.setAttribute("name", "zhangsan");
-
读取servletcontext的属性值
String name = (String)servletContext.getAttribute("name");
-
获取web，xml中配置的公共属性
-
<context-param> <param-name>chengdu</param-name> <param-value>beautiful</param-value> </context-param> <!-- 在xml配置中添加公共属性 --> -
String chengdu = servletContext.getInitParameter("chengdu");
-
-
获取项目下某个文件的绝对路径
String realPath = servletContext.getRealPath("web.xml");
-
获取web项目的上下文路径（虚拟目录路径）
String contextPath = servletContext.getContextPath();
public class ServletContextServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doGet(request, response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 设置编码
request.setCharacterEncoding("utf-8");
response.setCharacterEncoding("utf-8");
response.setContentType("text/html:charset=utf-8");
// 获取ServletContext
// 方式1
ServletContext servletContext = this.getServletContext();
// 方式2
ServletContext servletContext1 = this.getServletConfig().getServletContext();
// 方式3
ServletContext servletContext2 = request.getSession().getServletContext();
// servletcontext设置属性值
servletContext.setAttribute("name", "zhangsan");
// 读取servletcontext的属性值
String name = (String)servletContext.getAttribute("name");
// 从web和xml中获取参数值
String chengdu = servletContext.getInitParameter("chengdu");
System.out.println(chengdu);
// 获取项目下某个文件的绝对路径
String realPath = servletContext.getRealPath("web.xml");
System.out.println(realPath);
// 获取web项目的上下文路径
String contextPath = servletContext.getContextPath();
System.out.println(contextPath);
}
}
- 网页访问计数器
public class NumServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doGet(request, response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// 设置编码
request.setCharacterEncoding("utf-8");
response.setCharacterEncoding("gbk");
// 获取servletcontext对象
ServletContext servletContext = this.getServletContext();
// 获取属性值
Integer num = (Integer)servletContext.getAttribute("num");
if(num==null){
servletContext.setAttribute("num",1);
}else{
// 实现每次访问加1，并将num设置到ServletContext中
servletContext.setAttribute("num", ++num);
}
// 获取输出对象
PrintWriter out = response.getWriter();
// 给客户端返回数据
out.write("<html>");
out.write("<head>");
out.write("</head>");
out.write("<body>");
out.write("<h1>用户的访问次数为："+ num +"次</h1>");
out.write("</body>");
out.write("</html>");
}
}
