----------------------------- ServletContext的揭秘------------------------------

ServletContext

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，它代表当前web应用。
由于一个WEB应用中的所有Servlet共享同一个ServletContext对象，因此Servlet对象之间可以通过ServletContext对象来实现通讯。ServletContext对象通常也被称之为context域对象。
查看ServletContext API文档，了解ServletContext对象的功能。

应用:

获取WEB应用的全局初始化参数

通过ServletContext对象实现数据共享

- 案例--- 统计站点访问次数

利用ServletContext对象读取资源文件

Object	getAttribute`(`String `name)` Returns the servlet container attribute with the given name, or `null` if there is no attribute by that name.
String	getContextPath`()` Returns the context path of the web application.
String	getInitParameter`(`String `name)` Returns a `String` containing the value of the named context-wide initialization parameter, or `null` if the parameter does not exist.
String	getRealPath`(`String `path)` Returns a `String` containing the real path for a given virtual path
`void`	setAttribute`(`String `name,` Object `object)` Binds an object to a given attribute name in this servlet context.
`InputStream`	getResourceAsStream`(`String `path)` Returns the resource located at the named path as an `InputStream` object.

全局参数获取代码示例：

package com.rl.servlet;

import java.io.IOException;

import javax.servlet.ServletConfig;

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 ServletDemo1 extends HttpServlet {

@Override

public void init(ServletConfig config) throws ServletException {

//获得ServletContext对象

ServletContext sc = config.getServletContext();

//获得ServletContext级别的全局参数

String contextValue = sc.getInitParameter("context_key");

System.out.println(contextValue);

}

<?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_3_0.xsd" id="WebApp_ID" version="3.0">

<context-param>

<param-name>context_key</param-name>

<param-value>context_value</param-value>

</context-param>

<servlet-name>ServletDemo1</servlet-name>

<servlet-class>com.rl.servlet.ServletDemo1</servlet-class>

<load-on-startup>1</load-on-startup>

</servlet>

<servlet-mapping>

<servlet-name>ServletDemo1</servlet-name>

<url-pattern>/servletDemo1</url-pattern>

</servlet-mapping>

</web-app>

ServletContext的揭秘

全局属性设置代码示例：

package com.rl.servlet;

import java.io.IOException;

import javax.servlet.ServletConfig;

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 ServletDemo1 extends HttpServlet {

@Override

public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

//获得Servlet容器对象

ServletContext sc = getServletContext();

//获得全局属性

Integer pvcount = (Integer)sc.getAttribute("pvcount");

if(pvcount == null){

sc.setAttribute("pvcount", 1);

pvcount = (Integer)sc.getAttribute("pvcount");

}else{

sc.setAttribute("pvcount", ++pvcount);

}

response.getOutputStream().write(("<font color='red' size='20'> 当前站点被点击了" + pvcount +"次</font>").getBytes());

}

ServletContext的揭秘

通过ServletContext获得项目根目录下的文件：

package com.rl.servlet;

import java.io.IOException;

import java.io.InputStream;

import java.util.Properties;

import javax.servlet.ServletConfig;

import javax.servlet.ServletContext;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

public class ServletDemo3 extends HttpServlet {

@Override

public void init(ServletConfig config) throws ServletException {

//获得ServletContext对象

ServletContext sc = config.getServletContext();

//获得工程目录webroot下文件的路径

//D:\tomcat-test\apache-tomcat-7.0.62\webapps\servlet_demo4\test.properties

//getRealPath的参数内容不会被校验，只有真正要用这个路径的时候才知道路径对不对

String path = sc.getRealPath("test.properties");

System.out.println(path);

//获得工程目录webroot下文件的输入流对象

//第一个/代表项目的根目录

InputStream in = sc.getResourceAsStream("/WEB-INF/test.properties");

Properties prop = new Properties();

try {

prop.load(in);

System.out.println(prop.get("key"));

} catch (IOException e) {

e.printStackTrace();

}

读取类路径下文件的两种方式：

package com.rl.servlet;

import java.io.IOException;

import java.io.InputStream;

import java.util.Properties;

import javax.servlet.ServletConfig;

import javax.servlet.ServletContext;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

public class ServletDemo4 extends HttpServlet {

@Override

public void init(ServletConfig config) throws ServletException {

//获得ServletContext对象

ServletContext sc = config.getServletContext();

//获得classpath下的资源的文件的流

//由于classpath下的文件发布之后是在web项目/WEB-INF/classes下

//所以去指定/WEB-INF/classes/test1.properties

//InputStream in = sc.getResourceAsStream("/WEB-INF/classes/test1.properties");

//另一种方法获取类文件

//通过当前类获取类对象

//通过类对象获得类加载器

//通过类加载器获得资源流，资源流指定的根目录是classpath,也就是java项目的src文件夹

//使用类加载器的方式来读取classpath下的资源文件

//好处不依赖于ServletContext，任何类都可以获得classpath下的文件

//不需要再自己指定/WEB-INF/classes

InputStream in = this.getClass().getClassLoader().getResourceAsStream("test1.properties");

//读取test1.properties中的值

Properties prop = new Properties();

try {

prop.load(in);

System.out.println(prop.get("key1"));

} catch (IOException e) {

e.printStackTrace();

}

ServletContext的揭秘

ServletContext的揭秘

ServletContext

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