ServletContext对象
web容器在启动的时候，它会为每个web程序都创建一个对应的ServletContext对象， 它代表了当前的web应用;
共享数据
我在这个Servlet中保存的数据，可以在另外一个servlet中拿到;
1.新建一个javaweb的maven项目：
2.新建两个servlet：
HelloServlet：
package com.allen.servlet;
import javax.servlet.Servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class HelloServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//this.getInitParameter(); 初始化参数
//this.getServletConfig(); servlet配置
//this.getServletContext(); servlet上下文
ServletContext servletContext = this.getServletContext();
servletContext.setAttribute("userName", "allen"); //将一个数据保存到servlet中，键为userName，值为allen
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doGet(req, resp);
}
}GetServlet：
package com.allen.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class GetServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext servletContext = this.getServletContext();
String userName = (String) servletContext.getAttribute("userName");
resp.setContentType("text/html");
resp.setCharacterEncoding("utf-8");
resp.getWriter().print("名字：" + userName);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doGet(req, resp);
}
}web.xml:
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" version="4.0" metadata-complete="true"> <servlet> <servlet-name>hello</servlet-name> <servlet-class>com.allen.servlet.HelloServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>hello</servlet-name> <url-pattern>/hello</url-pattern> </servlet-mapping> <servlet> <servlet-name>getc</servlet-name> <servlet-class>com.allen.servlet.GetServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>getc</servlet-name> <url-pattern>/getc</url-pattern> </servlet-mapping> </web-app>
3.配置tomcat，启动测试：
第一次进入getc：
调用helloservlet之后：
结果：
获得初始化参数：
web.xml
<!-- 配置一些web应用的初始化参数 --> <context-param> <param-name>url</param-name> <param-value>jdbc:mysql://localhost:3306/mybatis</param-value> </context-param> <servlet> <servlet-name>ServletDemo03</servlet-name> <servlet-class>com.allen.servlet.ServletDemo03</servlet-class> </servlet> <servlet-mapping> <servlet-name>ServletDemo03</servlet-name> <url-pattern>/ServletDemo03</url-pattern> </servlet-mapping>
ServletDemo03
package com.allen.servlet;
import javax.servlet.Servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class ServletDemo03 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext servletContext = this.getServletContext();
String url = servletContext.getInitParameter("url");
resp.getWriter().print(url);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doGet(req, resp);
}
}访问ServletDemo03测试：
请求转发：
web.xml
<servlet> <servlet-name>ServletDemo04</servlet-name> <servlet-class>com.allen.servlet.ServletDemo04</servlet-class> </servlet> <servlet-mapping> <servlet-name>ServletDemo04</servlet-name> <url-pattern>/ServletDemo04</url-pattern> </servlet-mapping>
ServletDemo04
package com.allen.servlet;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class ServletDemo04 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext servletContext = this.getServletContext();
//RequestDispatcher requestDispatcher = servletContext.getRequestDispatcher("/ServletDemo03"); //转发的请求路径
//requestDispatcher.forward(req, resp); //调用forward实现转发
servletContext.getRequestDispatcher("/ServletDemo03").forward(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doGet(req, resp);
}
}访问ServletDemo04测试是否被转发到ServletDemo03：
读取资源文件：
Properties
在java目录下新建properties
●在resources目录下新建properties
发现:都被打包到了同一个路径下: classes, 我们俗称这个路径为classpath:
思路:需要一个文件流;
web.xml
<servlet> <servlet-name>ServletDemo05</servlet-name> <servlet-class>com.allen.servlet.ServletDemo05</servlet-class> </servlet> <servlet-mapping> <servlet-name>ServletDemo05</servlet-name> <url-pattern>/ServletDemo05</url-pattern> </servlet-mapping>
ServletDemo05
package com.allen.servlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;
public class ServletDemo05 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
InputStream in = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
Properties properties = new Properties();
properties.load(in);
String userName = properties.getProperty("userName");
String password = properties.getProperty("password");
resp.getWriter().print(userName + " " + password);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
this.doGet(req, resp);
}
}测试：
