ServletConfig
- Servlet配置文件中，可以使用一个或多个<init-param>标签配置一些初始化参数
- 创建实例对象时，自动将初始化参数封装到ServletConfig对象中，并在调用Servlet的init方法时，将Servletconfig对象传递给servlet。
<!-- 演示初始化参数 -->
<servlet>
<servlet-name>ServletDemo6</servlet-name>
<servlet-class>cn.servlet.ServletDemo6</servlet-class>
<!-- 配置初始化参数 -->
<init-param>
<param-name>username</param-name>
<param-value>root</param-value>
</init-param>
<init-param>
<param-name>password</param-name>
<param-value>123</param-value>
</init-param>
</servlet>
ServletConfig的几种方法：
- String getServletName() 得到当前servlet的名字
- String getInitParameter(String name) 通过参数名获得参数值
- java.util.Enumeration<E> getInitParameterNames() 将所有参数返回到一个枚举对象中
- ServletContext getServletContext() 返回ServletContext对象
public class ServletDemo6 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//测试ServletConfig对象的api
//先获取ServletCongig对象
ServletConfig config = getServletConfig();
//获取配置文件中servlet的名称
System.out.println("servlet的名称："+ config.getServletName());
//获取初始化参数
String username = config.getInitParameter("username");
String password = config.getInitParameter("password");
System.out.println(username + password);
Enumeration e = config.getInitParameterNames();
while(e.hasMoreElements()){
String name = (String)e.nextElement();
String value = config.getInitParameter(name);
System.out.println(name + value);
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
ServletContext对象（域对象）
- 每个web应用程序都创建一个对应的ServletContext对象，代表当前web应用
- 通过 ServletConfig.getServletContext方法获得该对象
- 一个web应用中所有Servlet共享同一个ServletContext对象，所以可以通过ServletContext实现通讯
- 应用
- 获取web应用的全局初始化参数
- String getInitParameter(String)
- getInitParameterNames()
- 通过ServletContext对象实现数据共享
- void setAttribute(String name, Object obj) 存入数据
- void removeAttribute(String name) 删除数据
- Object getAttribute(String name) 获取数据
- 利用ServletContext对象读取资源文件
- InputStream getResourceAsStream(String path) 通过文件的地址获取输入流
- String getRealPath(String path) 通过文件的地址获取文件的绝对路径
- 获取web应用的全局初始化参数
<!-- 配置全局的初始化参数 web.xml-->
<context-param>
<param-name>encoding</param-name>
<param-value>UTF-8</param-value>
</context-param>
public class ContextDemo1 extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//获取ServletContext对象
ServletContext context = getServletContext();
//读取全局的初始化参数
String encoding = context.getInitParameter("encoding");
System.out.println("编码:"+ encoding);
Enumeration e = context.getInitParameterNames();
while(e.hasMoreElements()){
String name = (String)e.nextElement();
String value = context.getInitParameter(name);
System.out.println(name + ":" +value);
}
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
public class CountServlet extends HttpServlet {
/**
* 实例被创建，调用init方法进行初始化
* 在域对象中存入一个变量，赋值为0
*/
public void init() throws ServletException {
//获取ServletContext对象
getServletContext().setAttribute("count", 0);
}
/**
* 每一次访问，都会执行该方法
* 拿出Count变量，值自增，存进去
*/
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
ServletContext context = getServletContext();
Integer count = (Integer)context.getAttribute("count");
context.setAttribute("count", ++count);
System.out.println("被访问了 ");
response.setContentType("text/html;charset=UTF-8");
response.getWriter().write("<h1>打野下次来</h1>");
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
//另一个servlet文件，用来显示网站显示次数
public class Show extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
Integer count = (Integer)getServletContext().getAttribute("count");
response.setContentType("text/html;charset=UTF-8");
response.getWriter().write("<h1>那个网站被访问了"+count+"次</h1>");
System.out.println("被访问了 ");
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
public class ReadServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
read2();
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
/**
* 通过ServletCOntext获取文件的绝对路径
* @throws IOException
*/
public void read3() throws IOException{
//获取对象
String path = getServletContext().getRealPath("/WEB-INF/classes/db.properties");
System.out.println(path);
InputStream in = getServletContext().getResourceAsStream(path);
//打印方式
print(in);
}
/**
* 获取src目录下的文件
* @throws IOException
*/
public void read2() throws IOException{
//ServletContext读取文件
InputStream in = getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
//打印方式
print(in);
}
/**
* 传统方式读取文件
* @throws IOException
*/
public void read1() throws IOException{
InputStream in = new FileInputStream("");
print(in);
}
/**
* 在控制台打印
* @throws IOException
*/
public void print(InputStream in) throws IOException{
Properties pro = new Properties();
pro.load(in);
//
String username = pro.getProperty("username");
String password = pro.getProperty("password");
String desc = pro.getProperty("desc");
System.out.println("用户名："+ username);
}
}
