/*
ServletConfig对象
·在Servlet的配置文件中，可以使用一个或多个<init-param>标签为servlet配置一些初始化参数。
·Servlet配置了初始化参数后，web容器在创建servlet实例对象时，会自动将这些初始化参数封装到ServletConfig对象中，
并在调用servlet的init方法时，将ServletConfig对象传递给servlet。进而，程序员通过ServletConfig对象就可以得到当前servlet的初始化参数信息。
ServletContext对象
一、原理简介:
·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。
·ServletConfig对象中维护了ServletContext对象的引用，开发人员在编写servlet时，可以通过ServletConfig.getServletContext方法获得ServletContext对象。
·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。
二、应用：
1、多个Servlet通过ServletContext对象实现数据共享。
2、获取WEB应用的初始化参数。
3、实现Servlet的转发。
4、利用ServletContext对象读取资源文件。
·得到文件路径
·读取资源文件的三种方式
·properties文件（属性文件）
*/
//多个servlet通过servletContext实现数据共享
public class ServletContextDemo1 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String data = "abcddffdf";
ServletContext context = this.getServletConfig().getServletContext();
context.setAttribute("data", data); //map
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
public class ServletContextDemo2 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
ServletContext context = this.getServletContext();
String data = (String) context.getAttribute("data");
System.out.println(data);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
//获取整个web站点的初始化参数
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
ServletContext context = this.getServletContext();
String url = context.getInitParameter("url");
System.out.println(url);
}
/*
用servletContext实现请求转发:mvc
注意：
·转发之前的所有写入都无效
·转发之前，response不能提交，否则转发的时候服务器会抛：Cannot forward after response has been committed
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.getOutputStream().write("111".getBytes());
ServletContext context = this.getServletContext();
RequestDispatcher rd = context.getRequestDispatcher("/servlet/ServletDemo2");
rd.forward(request, response);
response.getOutputStream().write("222".getBytes());
}
//读取资源文件的三种方式
//使用servletContext读取资源文件
public class ServletContextDemo1 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
/*
做web工程时，不建议采用传统方式读取文件数据
FileInputStream in = new FileInputStream("db.properties");
System.out.println(in);
*/
test1(response);
}
private void test1(HttpServletResponse response) throws IOException {
// 获取web资源的绝对路径后，再用传统方式得到该资源的文件流
String path = this.getServletContext().getRealPath(
"/WEB-INF/classes/db.properties");
FileInputStream in = new FileInputStream(path);
Properties prop = new Properties();
prop.load(in);
// 该方法的好处是可以得到资源的名称
String filename = path.substring(path.lastIndexOf("\\")+1);
String password = prop.getProperty("password");
System.out.println(filename + " " + password);
}
private void test2(HttpServletResponse response) throws IOException {
// 直接得到该资源文件以流的形式返回
InputStream in = this.getServletContext().getResourceAsStream(
"/WEB-INF/classes/db.properties");
Properties prop = new Properties();
prop.load(in);
String password = prop.getProperty("password");
System.out.println(password);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
//用类装载器读取资源文件
public class ServletContextDemo2 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//获取到装载当前类的类装载器
ClassLoader loader = ServletContextDemo2.class.getClassLoader();
//读取指定目录下的文件资源
//通过类装载器读取资源文件的注意事项:不适合装载大文件，否则会导致jvm内存溢出
InputStream in = loader.getResourceAsStream("he/junhua/Servlet/db.properties");
Properties prop = new Properties();
prop.load(in);
System.out.println(prop.getProperty("driver"));
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
//在Servlet外读取资源文件
public class ServletContextDemo3 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
Dao dao = new Dao();
dao.run();
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
public class Dao {
public void run() throws IOException {
URL url = Dao.class.getClassLoader().getResource("db2.properties");
String path = url.getPath();
FileInputStream in = new FileInputStream(path);
Properties prop = new Properties();
prop.load(in);
System.out.println(prop.size());
System.out.println(prop.getProperty("username"));
prop.setProperty("username", "xxx");
FileOutputStream out = new FileOutputStream(path);
prop.store(out, "");
System.out.println(prop.getProperty("username"));
out.close();
in.close();
}
}
//一个简单的应用：读取PranavMistry_2009I_480.mp4,并拷贝到e:\根目录下
public class ServletContextDemo5 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
ServletContext context = this.getServletContext();
//得到文件名
String path = context.getRealPath("/1.jpg");
String filename = path.substring(path.lastIndexOf("\\")+1);
//得到资源文件读的流,并写入指定目录
InputStream in = context.getResourceAsStream("/1.jpg");
byte buffer[] = new byte[1024];
int len = 0;
FileOutputStream out = new FileOutputStream("E:\\temp\\"+filename);
while((len=in.read(buffer))>0){
out.write(buffer,0,len);
}
out.close();
in.close();
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}