ServletContext

一、ServletContext(Servlet 上下文)

每个web工程都只有一个ServletContext对象。 说白了也就是不管在哪个servlet里面，获取到的这个类的对象都是同一个。

举例步骤：新建一个项目–java Resources–src右键新建Servlet–填写类名和包名

自动生成代码如下：

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package servleter;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class ServletContext01
 */
public class ServletContext01 extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public ServletContext01() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.getWriter().append("Served at: ").append(request.getContextPath());
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

###如何得到对象(和ServletConfig相似)

//1. 获取对象
    ServletContext context = getServletContext();

二、ServletContext获取全局参数

ServletConfig----在servlet里面对<init-paramd>写具体的参数

ServletContext---对根标签servlet外面对<context-param>写全局参数

使用了直接右键server所以不用自己配

web.xml的完整内容：

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<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>ServletRegister</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
  <context-param>     //在这加context-param标签!!!!!!!!!!!!!!!
    <param-name>address</param-name>
    <param-value>shenzhen</param-value>
  </context-param>
  
  <servlet>
    <servlet-name>Demo</servlet-name>
    <servlet-class>servlet.Demo</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Demo</servlet-name>
    <url-pattern>/Demo</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>ServletContext01</display-name>
    <servlet-name>ServletContext01</servlet-name>
    <servlet-class>servleter.ServletContext01</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ServletContext01</servlet-name>
    <url-pattern>/ServletContext01</url-pattern>
  </servlet-mapping>
  <servlet>
    <description></description>
    <display-name>ServletContext02</display-name>
    <servlet-name>ServletContext02</servlet-name>
    <servlet-class>servleter.ServletContext02</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>ServletContext02</servlet-name>
    <url-pattern>/ServletContext02</url-pattern>
  </servlet-mapping>
</web-app>

ServletContext01/02代码几乎一样都是创建对象然后输出

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public class ServletContext02 extends HttpServlet {
	
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//1.获取对象
			ServletContext context=getServletContext();
		//2.获得address		
			String address=context.getInitParameter("address");
			System.out.println("这是ServletContext02的address="+address);
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
			doGet(request, response);
	}
}

01通过浏览器去刷新/02通过eclipse自带的页面浏览器刷新

三、ServletContext获取Web应用中的资源

  1. 获取资源在tomcat里面的绝对路径(getRealpath()方法)

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public class Demo04 extends HttpServlet {
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//1.获取对象
			ServletContext context=getServletContext();
			String path=context.getRealPath("file/config.properties");   //获取给定的文件在服务器上面的绝对路径 ---如果“”里面没有东西意思就是找到根目录
				System.out.println("path="+path);
				
				 //1.创建属性对象
				Properties properties=new Properties(); 
				InputStream is=new FileInputStream(path);  //通过InputStream数据流连接path
				properties.load(is); //加载输入流
				
				//3.获取name属性的值
				String name=properties.getProperty("name");
				System.out.println("name="+name); 			
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		doGet(request, response);
	}

}

代码结果如下：

  1. ServletContext对象.getResourceAsStream获取资源流对象
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public class Demo04 extends HttpServlet {
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//test01(); 
		test02();
	}

	private void test02() throws IOException {
		//1.获取对象
		Properties properties=new Properties();
		ServletContext context=getServletContext();  //创建ServletContext对象
		InputStream is=context.getResourceAsStream("file/config.properties");  //直接写文件路径(不需要path)
		properties.load(is);	//加载文件
		//3.获取name属性的值
		String name=properties.getProperty("name");
		System.out.println("name22="+name);
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		doGet(request, response);
	}

}
  1. 通过classloader去获取web工程下的资源

  • ServletContext：
    　　
    a路径：F:\tomcat\apache-tomcat…\wtpwebapps\Demo04

  • ClassLoader：
    　　
    a路径：F:\tomcat\apache-tomcat…\wtpwebapps\Demo04\WEB-INF\classes

要想让classloader回到Demo03的位置：

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//获得该java文件吧内磨机片的class然后获取到加载这个class的虚拟机中的那个类加载器对象
InputStream is=this.getClass().getClassLoader().getResourceAsStream("../../file/config.properties");

四、ServletContext存取数据

此为web代码框架：

实现界面分析：

步骤：

  1. Client客户端：主要是要有两个html的客户端代码：
    login主要是有三个input标签分别是登录、注册、提交按钮；login_success是用来用href标签弹出网站成功登陆次数(通过ServletContext对象的getAttribute()方法获取loginservlet类中的count值)
  2. server服务器端：主要是两个类：
    CountServlet类只是获取LoginServlet类的ServletContext对象获取count输出
    LoginServlet主要分为两步骤：一是通过request的getParameter方法获取login.html输入的账户密码；二是通过ServletContext()对象的set/getAttribute方法获取和更改登陆成功数字。成功可以通过response的setStatus(302)方法设置状态码，然后通过setHeader方法跳转到预定的login_success.html页面。

LoginServlet类代码：

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public class LoginServlet extends HttpServlet {
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//1.获取数据
		String username=request.getParameter("username");  //request 包括请求的信息
		String password=request.getParameter("password");
		System.out.println(username+password);
		
		//2.校验数据
		PrintWriter pw=response.getWriter();  //response 响应数据给浏览器 
		
		if("admin".equals(username)&&"123".equals(password))
		{
			//System.out.println("登陆成功!");
			//pw.write("login success..");
			
		//1.成功的次数累计加一	
			Object obj=getServletContext().getAttribute("count");//使用ServeletContext对象的getAttribute方法获取count数
			
			//默认是0次
			int totalCount=0; //计数用
			if(obj!=null)
			{
				totalCount=(int) obj;  //如果不为0就把obj强转给计数用的totalCount
			}
			System.out.println("已经登陆成功的次数是："+totalCount);
			
			//给count赋新的值
			getServletContext().setAttribute("count",totalCount+1);  //输出之后可以使用ServletContext对象的setAttribute方法更改count数字(当前输出的数字加一付给count)
		
		//2.跳转到成功的界面
			//设置状态码
			response.setStatus(302);
			//定位----->跳转去 login_success.html		
			response.setHeader("Location","login_success.html");
		}
		else
		{
			System.out.println("登录失败！");
			pw.write("login failed..");
		}	
		
	}
	
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
			doGet(request, response);
	}

}

CountServlet类代码：

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public class CountServlet extends HttpServlet {
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {	
		//1.取值
		int count=(int) getServletContext().getAttribute("count");
			
		//2.输出到界面
		response.getWriter().write("当前网站成功登录总次数为"+count+"次");	
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		doGet(request, response);
	}

}

login_success.html代码：

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<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>

	<h2>登录成功了</h2>
	<a href="CountServlet">获取网站登录成功总数 </a>   <!--href找的是xml里面 url标签的内容-->
</body>
</html>

login.html代码：

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<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<h2>请输入以下内容，完成登陆</h2>
	<form action="LoginServlet" method="get">  <!--action找的是xml里面 url标签的内容-->
		账号:<input type="text" name="username"/><br>
		密码:<input type="text" name="password"/><br>
		<input type="submit" value="登录"/>
	</form>
</body>
</html>

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本文标题:ServletContext

文章作者:Larkkkkkkk

发布时间:2020年02月18日 - 14时02分

最后更新:2020年02月22日 - 21时10分

原始链接:https://larkkkkkkk.github.io/2020/02/18/ServletContext/

许可协议: "署名-非商用-相同方式共享 3.0" 转载请保留原文链接及作者。

文章目录
  1. 1. 一、ServletContext(Servlet 上下文)
  2. 2. 二、ServletContext获取全局参数
  3. 3. 三、ServletContext获取Web应用中的资源
  4. 4. 四、ServletContext存取数据
,