016_Servlet上下文

一. Servlet上下文

1. 每个web工程都只有一个ServletContext对象。也就是在同一个web工程里, 所有的servlet获取到的这个类的对象都是同一个。

2. 获取上下文对象: ServletContext context = getServletContext();

3. ServletContext 的作用

3.1. 获取全局配置参数;

3.2. 获取web工程中的资源;

3.3. 存取数据, servlet间共享数据。

4. ServletContext何时创建: 服务器启动的时候, 会为托管的每一个web应用程序, 创建一个ServletContext对象。

5. ServletContext何时销毁: 从服务器移除托管或者是关闭服务器。

6. ServletContext 的作用范围: 只要在这个项目里面, 都可以取。

二. ServletContext 获取全局配置参数

1. 新建一个UseServletContext的Web工程

2. 在下WebContent新建一个index.html

3. 编写index.html

<!DOCTYPE html>
<html><head><meta charset="UTF-8" /><title>servlet上下文</title></head><body><a href="GetContextParam.action">获取全局配置参数</a><br/></body>
</html>

4. 新建一个GetContextParam.java类

5. 编辑GetContextParam.java

package com.lywgames.myservlet;import java.io.IOException;
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 GetContextParam extends HttpServlet {private static final long serialVersionUID = 1L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 获取ServletContext对象ServletContext servletContext = getServletContext();// 获取全局配置参数String address = servletContext.getInitParameter("address");System.out.println("address = " + address);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

6. 编辑web.xml

7. 部署运行

8. 点击”获取全局配置参数”超链接, 控制台打印

三. ServletContext 获取资源

1. 在WebContent目录下, 新建一个file目录, 放入config.properties文件, 文件内容如下图:

2. servletContext.getRealPath("/"): 工程(项目)在tomcat里面的根目录。

C:\Users\lywgames\Desktop\software\apache-tomcat-7.0.52\wtpwebapps\UseServletContext\

3. 新建一个GetResources.java类

4. 编辑GetResources.java, 使用getRealPath获取资源

package com.lywgames.myservlet;import java.io.FileInputStream;
import java.io.IOException;
import java.util.Properties;
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 GetResources extends HttpServlet {private static final long serialVersionUID = 1L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 获取ServletContext对象ServletContext servletContext = getServletContext();/* servletContext.getRealPath("/"): 工程在tomcat里面的根目录。* C:\Users\lywgames\Desktop\software\apache-tomcat-7.0.52\wtpwebapps\UseServletContext\*/// 获取给定的文件在服务器上面的绝对路径String realPath = servletContext.getRealPath("file/config.properties");Properties properties = new Properties();properties.load(new FileInputStream(realPath));System.out.println("name = " + properties.getProperty("name"));}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

5. 编写web.xml

6. 编辑index.html

7. 部署运行项目

8. 点击”获取资源”超链接, 控制台打印

9. 使用servletContext.getResourceAsStream(“资源文件路径”)获取资源文件输入流, 资源文件路径之前的路径是工程在tomcat里面的根目录。资源文件路径必须存在, 否则返回null。继续编辑我们的GetResources.java

package com.lywgames.myservlet;import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
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 GetResources  extends HttpServlet {private static final long serialVersionUID = 1L;public void getRealPath() throws ServletException, IOException {// 获取ServletContext对象ServletContext servletContext = getServletContext();/* servletContext.getRealPath("/"): 工程在tomcat里面的根目录。* C:\Users\lywgames\Desktop\software\apache-tomcat-7.0.52\wtpwebapps\UseServletContext\*/// 获取给定的文件在服务器上面的绝对路径String realPath = servletContext.getRealPath("file/config.properties");Properties properties = new Properties();properties.load(new FileInputStream(realPath));System.out.println("name = " + properties.getProperty("name"));}@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 获取ServletContext对象ServletContext servletContext = getServletContext();// servletContext.getResourceAsStream使用工程在tomcat里面的根目录。InputStream is = servletContext.getResourceAsStream("file/config.properties");Properties properties = new Properties();properties.load(is);System.out.println("name = " + properties.getProperty("name"));}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

10. 类路径相对的是classes目录

11. 使用类路径获取资源, 继续编辑我们的GetResources.java

package com.lywgames.myservlet;import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
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 GetResources  extends HttpServlet {private static final long serialVersionUID = 1L;public void getRealPath() throws ServletException, IOException {// 获取ServletContext对象ServletContext servletContext = getServletContext();/* servletContext.getRealPath("/"): 工程在tomcat里面的根目录。* C:\Users\lywgames\Desktop\software\apache-tomcat-7.0.52\wtpwebapps\UseServletContext\*/// 获取给定的文件在服务器上面的绝对路径String realPath = servletContext.getRealPath("file/config.properties");Properties properties = new Properties();properties.load(new FileInputStream(realPath));System.out.println("name = " + properties.getProperty("name"));}public void getResourceAsStream() throws ServletException, IOException {// 获取ServletContext对象ServletContext servletContext = getServletContext();// servletContext.getResourceAsStream使用工程在tomcat里面的根目录。InputStream is = servletContext.getResourceAsStream("file/config.properties");Properties properties = new Properties();properties.load(is);System.out.println("name = " + properties.getProperty("name"));}@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 类路径相对于classes路径:C:\Users\lywgames\Desktop\software\apache-tomcat-7.0.52\wtpwebapps\UseServletContext\WEB-INF\classesInputStream is = this.getClass().getClassLoader().getResourceAsStream("../../file/config.properties");Properties properties = new Properties();properties.load(is);System.out.println("name = " + properties.getProperty("name"));}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

四. ServletContext存取数据, servlet间共享数据

1. 新建CunQuData.java和OutLoginCount.java

2. 编辑CunQuData.java

package com.lywgames.myservlet;import java.io.IOException;
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 CunQuData extends HttpServlet {private static final long serialVersionUID = 1L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 获取ServletContext对象ServletContext servletContext = getServletContext();Object loginCount =  servletContext.getAttribute("loginCount");if(loginCount != null){servletContext.setAttribute("loginCount", (((int)loginCount) + 1));}else{servletContext.setAttribute("loginCount", 1);}resp.sendRedirect("OutLoginCount.action");}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

3. 编辑OutLoginCount.java

package com.lywgames.myservlet;import java.io.IOException;
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 OutLoginCount extends HttpServlet {private static final long serialVersionUID = 1L;@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {// 获取ServletContext对象ServletContext servletContext = getServletContext();int loginCount =  (int)servletContext.getAttribute("loginCount");StringBuilder sb = new StringBuilder();sb.append("<!DOCTYPE html>").append("\r\n");sb.append("<html>").append("\r\n");sb.append("<head>").append("\r\n");// 网页编码UTF-8sb.append("<meta charset='UTF-8' />").append("\r\n");sb.append("<title>登录次数</title>").append("\r\n");sb.append("</head>").append("\r\n");sb.append("<body>").append("\r\n");sb.append("<h1>登录次数:").append(loginCount).append("</h1>").append("\r\n");sb.append("</body>").append("\r\n");sb.append("</html>");// 相应客户端的内容类型是text/html 编码是UTF-8(包含字符编码和网页编码)resp.setContentType("text/html;charset=UTF-8");// 字符流响应客户端resp.getWriter().println(sb.toString());}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}

4. 编辑index.html

5. 编辑web.xml

6. 部署运行项目

7. 多点击几次登录, 显示登录次数

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