ServletContext相关

我不是女神ヾ 2022-04-02 16:24 250阅读 0赞

简介

如何得到对象

有什么作用

1、获取全局配置参数

2、获取web工程中的资源

3、存取数据，servlet间共享数据 域对象

ServlerContext的生命周期

ServletContext 的作用范围

--------------------

# 简介 #

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。

--------------------

# 如何得到对象 #

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

# 有什么作用 #

1.  获取全局配置参数
2.  获取web工程中的资源
3.  存取数据，servlet间共享数据 域对象

## 1、获取全局配置参数 ##

web.xml中设置参数

<context-param>
        <param-name>name</param-name>
        <param-value>朱俊伟</param-value>
     </context-param>
    </web-app>

创建Servlet并配置Servlet并读取相应的参数

package com.zhujunwei.servletContext;
    
    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;
    /**
     * 
     * @author Administrator
     * 创建ServletContext读取全局变量的值
     *
     */
    public class ServletContext01 extends HttpServlet {
    	private static final long serialVersionUID = 1L;
    
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		//读取全局变量的值
    		ServletContext context = getServletContext();
    		String name = context.getInitParameter("name");
    		System.out.println(name);
    	}
    
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request, response);
    	}
    
    }

运行结果

朱俊伟

## 2、获取web工程中的资源 ##

如果在项目中存在配置文件想要读取（如config.properties），可采用如下三种方法：

config.properties文件所在目录

-WebContent
      -file
        -config.properties
      -META-INF
      -WEB-INF

config.properties文件内容

name=zhujunwei

读取的三种方法

package com.zhujunwei.servletContext;
    
    import java.io.FileInputStream;
    import java.io.FileNotFoundException;
    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;
    
    /**
     * 
     * @author Administrator 
     * 读取工程文件的三种方法
     *
     */
    public class ServletContext02 extends HttpServlet {
    	private static final long serialVersionUID = 1L;
    
    	protected void doGet(HttpServletRequest request, HttpServletResponse response)
    			throws ServletException, IOException {
    		getProperty1();
    		getProperty2();
    		getProperty3();
    	}
    	
    	/**
    	 * 方法3：通过类加载器读取工程中的文件
    	 * @throws IOException
    	 */
    	private void getProperty3() throws IOException {
    		// 1、创建属性对象
    		Properties properties = new Properties();
    
    		// 2、指定载入的数据源
    		InputStream inStream = this.getClass().getClassLoader().getResourceAsStream("../../file/config.properties");
    		properties.load(inStream);
    
    		// 3、获取name属性的值
    		String name = properties.getProperty("name");
    		System.out.println("getProperty3():name=" + name);
    	}
    
    	/**
    	 * 方法2：通过ServletContext中的getResourceAsStream方法读取文件
    	 * @throws IOException
    	 */
    	private void getProperty2() throws IOException {
    		// 获取ServletContext对象
    		ServletContext context = getServletContext();
    
    		// 1、创建属性对象
    		Properties properties = new Properties();
    
    		// 2、指定载入的数据源
    		InputStream inStream = context.getResourceAsStream("file/config.properties");
    		properties.load(inStream);
    
    		// 3、获取name属性的值
    		String name = properties.getProperty("name");
    		System.out.println("getProperty2():name=" + name);
    	}
    	
    	/**
    	 * 方法1：通过ServletContext中的getRealPath方法读取文件
    	 * @throws FileNotFoundException
    	 * @throws IOException
    	 */
    	private void getProperty1() throws FileNotFoundException, IOException {
    		// 获取ServletContext对象
    		ServletContext context = getServletContext();
    		// 获取给定的文件在服务器上面的绝对路径
    		String path = context.getRealPath("file/config.properties");
    
    		// 1、创建属性对象
    		Properties properties = new Properties();
    
    		// 2、指定载入的数据源
    		InputStream inStream = new FileInputStream(path);
    		properties.load(inStream);
    
    		// 3、获取name属性的值
    		String name = properties.getProperty("name");
    		System.out.println("getProperty1():name=" + name);
    	}
    
    	protected void doPost(HttpServletRequest request, HttpServletResponse response)
    			throws ServletException, IOException {
    		doGet(request, response);
    	}
    
    }

配置Servlet，执行得到结果

getProperty1():name=zhujunwei
    getProperty2():name=zhujunwei
    getProperty3():name=zhujunwei

## 3、存取数据，servlet间共享数据 域对象 ##

思路分析

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMyOTY1MTg3_size_16_color_FFFFFF_t_70][]

<!DOCTYPE html>
    <html>
    <head>
    	<meta charset="UTF-8">
    	<title>Insert title here</title>
    </head>
    <body>
    	<h2>请输入账号密码登录</h2>
    	<form action="LoginServlet" method="get">
    		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>

LoginServlet

package com.zhujunwei.servletContext;
    
    import java.io.IOException;
    import java.io.PrintWriter;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    /**
     * 从客户端取得用户输入的账号和密码，经过校验后跳转到指定的页面
     * @author Administrator
     *
     */
    public class LoginServlet extends HttpServlet {
    	private static final long serialVersionUID = 1L;
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		//获取客户端输入的值
    		String username = request.getParameter("username");
    		String password = request.getParameter("password");
    		
    		//对值进行校验并返回客户端
    		if("admin".equals(username)&&"123456".equals(password))
    		{
    			//1、成功次数的累加
    			//获取以前存的值，然后在旧的值基础上+1
    			Object obj = getServletContext().getAttribute("count");
    			//默认就是0次
    			int totalCount = 0;
    			if(obj!=null)
    			{
    				totalCount = (int) obj;
    			}
    			//给count赋新的值
    			getServletContext().setAttribute("count", totalCount+1);
    			//2、跳转到login_success.html
    			//设置状态码 ：重新定位状态码
    			response.setStatus(302);
    			//定位跳转的位置是哪一个页面
    			response.setHeader("Location", "login_success.html");
    		}
    		else
    		{
    			PrintWriter pw = response.getWriter();
    			pw.write("login filed...");
    		}
    	}
    
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request, response);
    	}
    
    }

<!DOCTYPE html>
    <html>
    <head>
    <meta charset="UTF-8">
    <title>Insert title here</title>
    </head>
    <body>
    	<h2>登录成功</h2>
    	<a href="ServletContext04">查看网页登录成功的次数。</a>
    </body>
    </html>

CountServlet

package com.zhujunwei.servletContext;
    
    import java.io.IOException;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    public class CountServlet extends HttpServlet {
    	private static final long serialVersionUID = 1L;
    	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		//取值
    		int count = (int) getServletContext().getAttribute("count");
    		//输出到界面
    		response.getWriter().write("Login Success Count:"+count);
    	}
    
    	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    		doGet(request, response);
    	}
    
    }

运行结果

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMyOTY1MTg3_size_16_color_FFFFFF_t_70 1][]

![20181227231900128.png][]

![20181227231924231.png][]

# ServlerContext的生命周期 #

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

从服务器移除托管，或者是关闭服务器。

# ServletContext 的作用范围 #

只要在这个项目里面，都可以取。 只要同一个项目。 A项目存，在B项目取，是取不到的，因为ServletContext对象不同。

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMyOTY1MTg3_size_16_color_FFFFFF_t_70]: /images/20220402/818f31dfdb7d45d18a3403034fc6b863.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzMyOTY1MTg3_size_16_color_FFFFFF_t_70 1]: /images/20220402/0054e42686f047b08fcc51b9b9341aad.png
[20181227231900128.png]: /images/20220402/916b8124aaed4e3fb0f2c414ab6b1506.png
[20181227231924231.png]: /images/20220402/46d986bbc3d74455ba39b5b2628ec9a2.png