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ServletContext对象
概述
- 全局对象，拥有作用域，对应Tomcat的Web应用
- Web服务器启动时，会为每一个Web应用程序创建一块共享的存储区域（ServletContext）
- ServletContext在Web服务器
启动时创建，服务器关闭时销毁
获取ServletContext对象
- GenericServlet提供 getServletContext(); 方法 this.getServletContext();
- HttpServletRequest提供 getServletContext(); 方法
- HttpSession提供 getServletContext(); 方法
//获取ServletContext对象
ServletContext servletContext = this.getServletContext();
//通过request对象，获取ServletContext对象
ServletContext servletContext1 = request.getServletContext();
//通过request获取session对象，获取ServletContext对象
HttpSession session = request.getSession();
ServletContext servletContext2 = session.getServletContext();ServletContext 作用
• 获取项目真实路径（获取当前项目在服务器发布的真实路径）
String realpath = servletContext.getRealPath("/")；//获取ServletContext对象
ServletContext servletContext = this.getServletContext();
//获取项目真实路径
System.out.println(servletContext.getRealPath("/"));
/*
输出结果
D:Eclipseapache-tomcat-8.5.82-windows-x64apache-tomcat-8.5.82webappsServlet_Projects_war
*/
• 获取项目上下文路径（获取当前项目上下文路径：应用程序名称）
System.out.println(servletContext.getContextPath());
System.out.println(request.getContextPath());//获取ServletContext对象
ServletContext servletContext = this.getServletContext();
//获取项目上下文路径
System.out.println(servletContext.getContextPath());
System.out.println(request.getContextPath());
/*
输出结果：
/Servlet_Projects_war
/Servlet_Projects_war
*/
• 全局容器
ServletContext拥有作用域，可以存储数据到全局容器中
• 存储数据： servletContext.setAttribute(“name”,“服务器托管网value”);
• 获取数据： servletContext.getAttribute(“name”);
• 移除数据： servletContext.removeAttribute(“name”);
• ServletContextController类
@WebServlet(name = "ServletContextController", value = "/ctxController")
public class ServletContextController extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//获取ServletContext对象
ServletContext servletContext = this.getServletContext();
//获取项目真实路径
System.out.println(servletContext.getRealPath("/"));
//存储数据
servletContext.setAttribute("context","info");
}
}
• ShowContextController类
@WebServlet(name = "ShowContextController", value = "/ShowController")
public class ShowContextController extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//获取ServletContext对象
ServletContext servletContext = this.getServletContext();
//获取数据
String context = (String) servletContext.getAttribute("context");
System.out.println(context);
/*
输出结果：
D:Eclipseapache-tomcat-8.5.82-windows-x64apache-tomcat-8.5.82webappsServlet_Projects_war
info
*/
}
}ServletContext 特点
- 唯一性：一个应用对应一个ServletContext
- 生命周期：只要容器不关闭或者应用不卸载，ServletContext就一直存在
ServletContext 应用场景
• CounterController类
@WebServlet(name = "CounterController", value = "/counterController")
public class CounterController extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletRes服务器托管网ponse response) throws ServletException, IOException {
doPost(request, response);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//获取ServletContext对象
ServletContext servletContext = request.getServletContext();
//获取计数器
Integer counter = (Integer) servletContext.getAttribute("counter");
//计数器初始化
if (counter == null) {
counter = 1;
//counter存入计数器
servletContext.setAttribute("counter", counter);
} else {
counter++;
servletContext.setAttribute("counter", counter);
}
System.out.println("counter:" + counter);
}
}
• ShowCounterController类
@WebServlet(name = "ShowCounterController", value = "/ShowCounterController")
public class ShowCounterController extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//获取ServletContext对象
ServletContext servletContext = request.getServletContext();
//获取计数器
Integer counter = (Integer) servletContext.getAttribute("counter");
//计数器初始化
if (counter == null) {
counter = 1;
//counter存入计数器
servletContext.setAttribute("counter", counter);
} else {
counter++;
servletContext.setAttribute("counter", counter);
}
System.out.println("show:" + counter);
}
}
• 结果
counter:1
show:2
show:3
show:4
show:5
show:6
show:7作用域总结
- HttpServletRequest：一次请求，请求响应之前有效
- HttpSession：一次会话开始，浏览器不关闭或不超时之前有效
- ServletContext：服务器启动开始，服务器停止之前有效
结语：创作不易，如果觉得博主的文章赏心悦目，还请——
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