Servlet（二）

通过servletCOnfig获取servlet配置的初始化参数

<servlet>
    <servlet-name>ServletDemo4</servlet-name>
    <servlet-class>cn.itcast.web.servlet.ServletDemo4</servlet-class>
    <init-param>  <!-- servletConfig -->
    	<param-name>charset</param-name>
    	<param-value>UTF-8</param-value>
    </init-param>
    <init-param>  <!-- servletConfig -->
    	<param-name>xxx</param-name>
    	<param-value>yyy</param-value>
    </init-param>
</servlet>

ServletConfig config = this.getServletConfig();	
//获取配置的初始化参数的方式1 
//String value = config.getInitParameter("charset");		
Enumeration e = config.getInitParameterNames();
while(e.hasMoreElements()){
	String name = (String) e.nextElement();
	String value = config.getInitParameter(name);
	System.out.println(name + "=" + value);
}

通过servletContexg,获取为web应用配置的初始化参数

<!-- 为web应用设置初始化参数，这些设置的初始化参数可以通过servletContext对象的getInitParameter()方法获取 -->
  <context-param>
  	<param-name>url</param-name>
  	<param-value>jdbc:mysql://localhost:3306/test</param-value>
  </context-param>
  
  <context-param>
  	<param-name>username</param-name>
  	<param-value>root</param-value>
  </context-param>
  
  <context-param>
  	<param-name>password</param-name>
  	<param-value>root</param-value>
  </context-param>

//String value = this.getServletContext().getInitParameter("xxx");
String url = this.getServletContext().getInitParameter("url");
String username = this.getServletContext().getInitParameter("username");
String password = this.getServletContext().getInitParameter("password");

通过servletContext获取文件的mime类型

String filename = "1.jpg";
ServletContext context = this.getServletContext();
System.out.println(context.getMimeType(filename));	
response.setHeader("content-type", "image/jpeg");

获取web.xml文件中配置的web应用的显示名称

<display-name>ProjectName</display-name>

String name = this.getServletContext().getServletContextName();

//设置浏览器的缓存

long expriestime = System.currentTimeMillis() + 1*24*60*60*1000;(one day)
response.setDateHeader("expires", expriestime);
String data = "adsdfsdfsdfsdfdsf";
response.getWriter().write(data);

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用servletContext读取web工程不同位置的资源文件

url=jdbc:mysql://localhost:3306/test
username=root
password=root

//读取配置文件的第一种方式		
ServletContext context = this.getServletContext();
InputStream in = context.getResourceAsStream("/db.properties");	
Properties prop = new Properties();  //map
prop.load(in);				
String url = prop.getProperty("url");
String username = prop.getProperty("username");
String password = prop.getProperty("password");

//读取配置文件的第二种方式
ServletContext context = this.getServletContext();
String realpath = context.getRealPath("/db.properties"); 
//获取到操作文件名  
String filename = realpath.substring(realpath.lastIndexOf("\\")+1);
System.out.println("当前读到的文件是：" + filename);
FileInputStream in = new FileInputStream(realpath);
Properties prop = new Properties();
prop.load(in);	
String url = prop.getProperty("url");
String username = prop.getProperty("username");
String password = prop.getProperty("password");

//读取配置文件的第三种方式
ServletContext context = this.getServletContext();
URL url = context.getResource("/resource/db.properties");
InputStream in = url.openStream();
Properties prop = new Properties();
prop.load(in);	
String urlStr = prop.getProperty("url");
String username = prop.getProperty("username");
String password = prop.getProperty("password");

//读取src下面的配置文件
InputStream in = this.getServletContext().getResourceAsStream("/WEB-INF/classes/db.properties");
Properties prop = new Properties();  //map
prop.load(in);				
String url = prop.getProperty("url");
String username = prop.getProperty("username");
String password = prop.getProperty("password");

 在web工程的普通java程序中如何读取资源文件

ClassLoader loader = StudentDao.class.getClassLoader();
URL url = loader.getResource("com/dao/db.properties");
String filepath = url.getPath();
FileInputStream in = new FileInputStream(filepath);
Properties prop = new Properties();  //map
prop.load(in);	
String dburl = prop.getProperty("url");
String username = prop.getProperty("username");
String password = prop.getProperty("password");