《深入浅出 Servlet：Java Web 开发的基石》（二）

<servlet>
    <servlet-name>hello</servlet-name>
    <servlet-class>cn.tx.servlet.Servlet1</servlet-class>
    <init-param>
        <param-name>username</param-name>
        <param-value>root</param-value>
    </init-param>
    <init-param>
        <param-name>password</param-name>
        <param-value>txjava</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
</servlet>

String username = Cservletonfig.getInitParameter("username");
System.out.println("username:"+username);
Enumeration<String> parameterNames = servletConfig.getInitParameterNames();
while (parameterNames.hasMoreElements()){
    String element = parameterNames.nextElement();
    System.out.println(element+":"+servletConfig.getInitParameter(element));
}

 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.

<context-param>
    <param-name>company</param-name>
    <param-value>达内教育</param-value>
</context-param>

ServletContext servletContext = config.getServletContext();
String company = servletContext.getInitParameter("company");
System.out.println("company:"+company);

@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    doPost(request, response);
}

@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    ServletContext servletContext = getServletContext();
    Integer visitNums = (Integer)(servletContext.getAttribute("visitNums"));
    visitNums = visitNums == null ? 0 : visitNums;
    servletContext.setAttribute("visitNums",++visitNums);
    response.setCharacterEncoding("UTF-8");
    response.getWriter().write("当前网站访问人次:"+visitNums);
}

// 获得到ServletContext对象
ServletContext servletContext = config.getServletContext();

// 获得工程目录web下文件的绝对路径 D:\workspace\idea\servlet-demo1\out\artifacts\servlet_demo1_war_exploded\tx.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 = servletContext.getRealPath("tx.properties");

String path = servletContext.getRealPath("tx.properties");
System.out.println(path);
try {
    InputStream is = new FileInputStream(path);
    Properties p = new Properties();
    p.load(is);
    String username = p.getProperty("username");
    System.out.println(username);
} catch (Exception e)

    e.printStackTrace();
}

//获得工程目录web下文件的流第一个/代表项目的根目录
InputStream is = servletContext.getResourceAsStream("/WEB-INF/tx1.properties");

//使用类加载器的方式来读取classpath下的资源文件，好处不依赖与ServletContext，任何类都可以获得classpath下的资源文件，
//不需要再自己指定/WEB-INF/classes
InputStream is = this.getClass().getClassLoader().getResourceAsStream("tx2.properties");