Web容器在启动时,它会为每个Web应用程序都创建一个对应的ServletContext对象,这个对象代表当前Web应用。并且它被所有客户端共享(比如你在淘宝登陆了,那你的登陆信息会被带到很多页面,就是跳到其他页面发现也是登陆上的)。
package com.cheng.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;
import java.io.PrintWriter;
public class HelloServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext();
String username = "万里顾一程";//数据
context.setAttribute("username", "万里顾一程");//将一个数据保存在ServletContext中,username=万里顾一程
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
hello
com.cheng.servlet.HelloServlet
hello
/hello
package com.cheng.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 context = this.getServletContext();
String attribute = (String) context.getAttribute("username");//返回值,并类型强转为String
resp.setContentType("text/html");
resp.setCharacterEncoding("utf-8");
resp.getWriter().print("名字="+attribute);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
hello1
com.cheng.servlet.GetServlet
hello1
/hello1
在 web.xml 里配置的初始化参数可以用getInitParameter()
方法获取
url
jdbc:mysql://localhost:3306/mybatis
package com.cheng.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 ServletDemon03 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext();
String url = context.getInitParameter("url");
resp.getWriter().print(url);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
hello3
com.cheng.servlet.ServletDemon03
hello3
/hello3
/hello3
的 ServletDemon03
,继续编写一个能处理 /hello4
的 ServletDemon04
, ServletDemon04
在收到浏览器的请求后,它并不自己发送响应,而是把请求和响应都转发给路径为 /hello3
的 ServletDemon03
,后续请求的处理实际上是由 ServletDemon03
完成的。这种处理方式称为转发( Forward )
流程图如下所示:
package com.cheng.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;
/**
* @User len
* @Classname com.cheng.servlet.ServletDemon04
* @Project javaweb-01-servlet
* @Description TODO
* @Author wpcheng
* @Create 2021-02-06-18:36
* @Version 1.0
*/
public class ServletDemon04 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext context = this.getServletContext();
//RequestDispatcher 代表请求的派发者, 只能使用绝对路径
RequestDispatcher dispatcher = context.getRequestDispatcher("/hello3");//请求的是地址为/hello3的资源,因此该请求是由路径为/hello3的servlet实现的
dispatcher.forward(req,resp);//内部转发
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
hello4
com.cheng.servlet.ServletDemon04
hello4
/hello4
hello3
com.cheng.servlet.ServletDemon03
hello3
/hello3
类路径:即发布到Tomcat服务器后的ClassPath路径,在classes目录下 Properties可以用来保存属性集(类似Map, 以键值的形式保存数据,不同的是Properties都是String类型的)。这个类的优势是可以从流中获得属性集,或者把属性集报错到流中。 获取配置文件的信息
username=root
password=123456
package com.cheng.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 ServletDemon05 extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// “ / ”代表了当前工程的根目录
InputStream is = this.getServletContext().getResourceAsStream("/WEB-INF/classes/jdbc.properties");
Properties prop = new Properties();
prop.load(is);//下载文件流
String user = prop.getProperty("username");//通过键获取属性
String pwd = prop.getProperty("password");
resp.getWriter().println(user);
resp.getWriter().println(pwd);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
hello5
com.cheng.servlet.ServletDemon05
hello5
/hello5