JAVAWeb开发之Servlet-18.Servlet共享变量与变量的作用域

2021-09-05 08:58:53

–共享变量
? setAttribute
? getAttribute
–变量的作用域
? ServletContext
? HttpSession
? HttpServletRequest
–实例
? 测试变量的作用域

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? 共享变量
–无论对象的作用域如何，共享变量和获得变量的
方法都是一致的
? 共享变量
–setAttribute(“varName”,obj);
? 获得变量
–getAttribute（“varName”）；

? 变量的作用域
–在Servlet中有三个作用域
? ServletContext
–范围最大，应用程序级别的，整个应用程序都能访问
? HttpSession
–次之，会话级别的，在当前的浏览器中都能访问
? HttpServletRequest
–范围最小，请求级别，请求结束，变量的作用域也结束

? 实例
–测试变量的作用域

同一页面测试变量

ScopeServlet.java

package com.michael.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;
import javax.servlet.http.HttpSession;

public class ScopeServlet extends HttpServlet {

 /**
 * Constructor of the object.
 */
 public ScopeServlet() {
 super();
 }

 /**
 * Destruction of the servlet. 
 */
 public void destroy() {
 super.destroy(); // Just puts "destroy" string in log
 // Put your code here
 }

 /**
 * The doGet method of the servlet. 
 *
 * This method is called when a form has its tag value method equals to get.
 *
 * @param request the request send by the client to the server
 * @param response the response send by the server to the client
 * @throws ServletException if an error occurred
 * @throws IOException if an error occurred
 */
 public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 doPost(request,response);
 }

 /**
 * The doPost method of the servlet. 
 *
 * This method is called when a form has its tag value method equals to post.
 *
 * @param request the request send by the client to the server
 * @param response the response send by the server to the client
 * @throws ServletException if an error occurred
 * @throws IOException if an error occurred
 */
 public void doPost(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {
 // 1
 ServletContext sc = this.getServletContext();
 sc.setAttribute("sc_name", "sc_value");
 // 2
 HttpSession session = request.getSession();
 session.setAttribute("session_name", "session_value");
 // 3
 request.setAttribute("request_name", "request_value");
 String sc_value = (String) sc.getAttribute("sc_name");
 String session_value = (String) session.getAttribute("session_name");
 String request_value = (String) request.getAttribute("request_name");

 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>A Servlet</TITLE></HEAD>");
 out.println(" <BODY>");
 out.print(sc_value);
 out.print(session_value);
 out.println(request_value);
 out.println(" </BODY>");
 out.println("</HTML>");
 out.flush();
 out.close();
 }

 /**
 * Initialization of the servlet. 
 *
 * @throws ServletException if an error occure
 */
 public void init() throws ServletException {
 // Put your code here
 }

}

获取同一页面变量

两页面获取变量

ScopeServlet2.java

package com.michael.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;
import javax.servlet.http.HttpSession;

public class ScopeServlet2 extends HttpServlet {

 /**
 * Constructor of the object.
 */
 public ScopeServlet2() {
 super();
 }

 /**
 * Destruction of the servlet. 
 */
 public void destroy() {
 super.destroy(); // Just puts "destroy" string in log
 // Put your code here
 }

 /**
 * The doGet method of the servlet. 
 *
 * This method is called when a form has its tag value method equals to get.
 *
 * @param request the request send by the client to the server
 * @param response the response send by the server to the client
 * @throws ServletException if an error occurred
 * @throws IOException if an error occurred
 */
 public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 doPost(request,response);
 }

 /**
 * The doPost method of the servlet. 
 *
 * This method is called when a form has its tag value method equals to post.
 *
 * @param request the request send by the client to the server
 * @param response the response send by the server to the client
 * @throws ServletException if an error occurred
 * @throws IOException if an error occurred
 */
 public void doPost(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {
 ServletContext sc = this.getServletContext();
 HttpSession session = request.getSession();
 String sc_value = (String) sc.getAttribute("sc_name");
 String session_value = (String) session.getAttribute("session_name");
 String request_value = (String) request.getAttribute("request_name");

 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>A Servlet</TITLE></HEAD>");
 out.println(" <BODY>");
 out.println(sc_value);
 out.println(session_value);
 out.println(request_value);
 out.println(" </BODY>");
 out.println("</HTML>");
 out.flush();
 out.close();
 }

 /**
 * Initialization of the servlet. 
 *
 * @throws ServletException if an error occure
 */
 public void init() throws ServletException {
 // Put your code here
 }

}

测试第二个页面获取共享变量

打开第二个页面测试

由ScopeServlet跳转转发到ScopeServlet3页面

ScopeServlet.java

package com.michael.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;
import javax.servlet.http.HttpSession;

public class ScopeServlet extends HttpServlet {

 /**
 * Constructor of the object.
 */
 public ScopeServlet() {
 super();
 }

 /**
 * Destruction of the servlet. 
 */
 public void destroy() {
 super.destroy(); // Just puts "destroy" string in log
 // Put your code here
 }

 /**
 * The doGet method of the servlet. 
 *
 * This method is called when a form has its tag value method equals to get.
 *
 * @param request the request send by the client to the server
 * @param response the response send by the server to the client
 * @throws ServletException if an error occurred
 * @throws IOException if an error occurred
 */
 public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 doPost(request,response);
 }

 /**
 * The doPost method of the servlet. 
 *
 * This method is called when a form has its tag value method equals to post.
 *
 * @param request the request send by the client to the server
 * @param response the response send by the server to the client
 * @throws ServletException if an error occurred
 * @throws IOException if an error occurred
 */
 public void doPost(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {
 // 1
 ServletContext sc = this.getServletContext();
 sc.setAttribute("sc_name", "sc_value");
 // 2
 HttpSession session = request.getSession();
 session.setAttribute("session_name", "session_value");
 // 3
 request.setAttribute("request_name", "request_value");
 request.getRequestDispatcher("/servlet/ScopeServlet3").forward(request, response);
 /*
 String sc_value = (String) sc.getAttribute("sc_name");
 String session_value = (String) session.getAttribute("session_name");
 String request_value = (String) request.getAttribute("request_name");

 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>A Servlet</TITLE></HEAD>");
 out.println(" <BODY>");
 out.print(sc_value);
 out.print(session_value);
 out.println(request_value);
 out.println(" </BODY>");
 out.println("</HTML>");
 out.flush();
 out.close();
 **/
 }

 /**
 * Initialization of the servlet. 
 *
 * @throws ServletException if an error occure
 */
 public void init() throws ServletException {
 // Put your code here
 }

}

ScopeServlet3.java

package com.michael.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;
import javax.servlet.http.HttpSession;

public class ScopeServlet3 extends HttpServlet {

 /**
 * Constructor of the object.
 */
 public ScopeServlet3() {
 super();
 }

 /**
 * Destruction of the servlet. 
 */
 public void destroy() {
 super.destroy(); // Just puts "destroy" string in log
 // Put your code here
 }

 /**
 * The doGet method of the servlet. 
 *
 * This method is called when a form has its tag value method equals to get.
 *
 * @param request the request send by the client to the server
 * @param response the response send by the server to the client
 * @throws ServletException if an error occurred
 * @throws IOException if an error occurred
 */
 public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 doPost(request,response);
 }

 /**
 * The doPost method of the servlet. 
 *
 * This method is called when a form has its tag value method equals to post.
 *
 * @param request the request send by the client to the server
 * @param response the response send by the server to the client
 * @throws ServletException if an error occurred
 * @throws IOException if an error occurred
 */
 public void doPost(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 ServletContext sc = this.getServletContext();
 HttpSession session = request.getSession();
 String sc_value = (String) sc.getAttribute("sc_name");
 String session_value = (String) session.getAttribute("session_name");
 String request_value = (String) request.getAttribute("request_name");

 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>A Servlet</TITLE></HEAD>");
 out.println(" <BODY>");
 out.println(" <h1>");
 out.println("ScopeServlet3");
 out.println(" </h1>");
 out.println(sc_value);
 out.println(session_value);
 out.println(request_value);
 out.println(" </BODY>");
 out.println("</HTML>");
 out.flush();
 out.close();
 }

 /**
 * Initialization of the servlet. 
 *
 * @throws ServletException if an error occure
 */
 public void init() throws ServletException {
 // Put your code here
 }

}

超链接跳转测试

ScopeServlet.java

package com.michael.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;
import javax.servlet.http.HttpSession;

public class ScopeServlet extends HttpServlet {

 /**
 * Constructor of the object.
 */
 public ScopeServlet() {
 super();
 }

 /**
 * Destruction of the servlet. 
 */
 public void destroy() {
 super.destroy(); // Just puts "destroy" string in log
 // Put your code here
 }

 /**
 * The doGet method of the servlet. 
 *
 * This method is called when a form has its tag value method equals to get.
 *
 * @param request the request send by the client to the server
 * @param response the response send by the server to the client
 * @throws ServletException if an error occurred
 * @throws IOException if an error occurred
 */
 public void doGet(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {

 doPost(request,response);
 }

 /**
 * The doPost method of the servlet. 
 *
 * This method is called when a form has its tag value method equals to post.
 *
 * @param request the request send by the client to the server
 * @param response the response send by the server to the client
 * @throws ServletException if an error occurred
 * @throws IOException if an error occurred
 */
 public void doPost(HttpServletRequest request, HttpServletResponse response)
 throws ServletException, IOException {
 // 1
 ServletContext sc = this.getServletContext();
 sc.setAttribute("sc_name", "sc_value");
 // 2
 HttpSession session = request.getSession();
 session.setAttribute("session_name", "session_value");
 // 3
 request.setAttribute("request_name", "request_value");
 //request.getRequestDispatcher("/servlet/ScopeServlet3").forward(request, response);
 /*String sc_value = (String) sc.getAttribute("sc_name");
 String session_value = (String) session.getAttribute("session_name");
 String request_value = (String) request.getAttribute("request_name");**/

 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>A Servlet</TITLE></HEAD>");
 out.println(" <BODY>");
 out.println(" <a href=/Servlet_Scope/servlet/ScopeServlet3>");
 out.println(" ScopeServlet3");
 out.println(" </a>");
 /*out.print(sc_value);
 out.print(session_value);
 out.println(request_value);**/
 out.println(" </BODY>");
 out.println("</HTML>");
 out.flush();
 out.close();
 }

 /**
 * Initialization of the servlet. 
 *
 * @throws ServletException if an error occure
 */
 public void init() throws ServletException {
 // Put your code here
 }

}

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本文转自redking51CTO博客，原文链接：http://blog.51cto.com/redking/273398，如需转载请自行联系原作者

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