1、獲得整個web應用初始化參數
類中：
public class ContextServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//通過config獲得context
ServletContext context=getServletConfig().getServletContext();
//從而獲得全局的參數
System.out.println(context.getInitParameter("hobby"));//一定不能忘記用context
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
web.xml中：
<context-param>
<param-name>hobby</param-name>
<param-value>唱兒歌</param-value>
</context-param>
2、實現全局數據共享
以記錄網站的訪問次數爲例
在countServlet
類中
public class countServlet extends HttpServlet {
@Override
public void init() throws ServletException {
//獲得servletcontext對象
ServletContext context=getServletContext();
//保存訪問次數0
context.setAttribute("visitimes",0);
}
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//每次訪問都回執行doget方法，因此把遞增次數的訪問次數放在doget中。
//從servletcontext中獲得訪問次數
ServletContext context=getServletContext();
int times=(Integer)context.getAttribute("visitimes");
//訪問次數遞增
times++;
//更新訪問次數到servletcontext中
context.setAttribute("visitimes", times);
response.getWriter().print("網站被訪問了"+times+"次");//輸出到瀏覽器！
//System.out.println("網站被訪問了"+times+"次");
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
在CountShowServlet類中（代碼和上個類中的代碼一致！）
public class CountShowServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
/*ServletContext context=getServletContext();
int times =(Integer)context.getAttribute("visitimes");*/
ServletContext context=getServletContext();
int time=(Integer)context.getAttribute("visitimes");
time++;
context.setAttribute("visitimes", time);
response.getWriter().print(time);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
}
此例說明了在countServlet中用context記錄的訪問次數，在CountShowServlet
也能訪問，即全局共享！
3、讀取we工程資源文件
package aweiyo.io;
public class ReadFileServlet extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
//因爲不在wenroot的路徑下，而在工程路徑下，所以要加上前面的路徑。又因爲工程的存放文件的路徑是在webroot的目錄下，所以可以read，但是
//web-inf目錄下的文件就不可以讀取了，因爲其不在webroot的目錄下
String filename2="/WEB-INF/classes/a.txt";
filename2=getServletContext().getRealPath(filename2);
readfile(filename2);
// 路徑開頭必須寫/，因爲webroot就是servlet重的根目錄，所以在webroot下的文件不用加其他的
String filename="/a2.txt";
//獲得該路徑的絕對路徑，即全部路徑
filename=getServletContext().getRealPath(filename);
readfile(filename);
//用Class的路徑，也可用於Java中
Class c=ReadFileServlet.class;
String filename3=c.getResource("/a.txt").getFile();
readfile(filename3);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
doGet(request, response);
}
public static void readfile(String filename) throws FileNotFoundException,
IOException {
BufferedReader in =new BufferedReader(new FileReader(filename));
String line;
while((line=in.readLine())!=null){
System.out.println(line);
}
in.close();
}
}
注：java讀取文件
/**
* 通過Java程序讀取文件
* @author aweiyoo
*
*/
public class FileReaderTest {
public static void main(String[] args) throws IOException {
String filename="src/a.txt";
readfile(filename);
String filename2="WebRoot/a2.txt";
readfile(filename2);
String filename3=("a3.txt");//位於根目錄下的文件可以直接寫
readfile(filename3);
}
public static void readfile(String filename) throws FileNotFoundException,
IOException {
BufferedReader in =new BufferedReader(new FileReader(filename));
String line;
while((line=in.readLine())!=null){
System.out.println(line);
}
in.close();
}
}