ServletContextListener的使用

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Java Servlet SQL 应用服务器 Web

1：ServletContext对象是一个为整个web应用提供共享的内存，任何请求都可以访问里面的内容
2：如何实现在服务启动的时候就动态的加入到里面的内容：我们需要做的有：
1）实现servletContextListerner接口并将要共享的通过setAttribute（name,data）方法提交到内存中去
2）应用项目在通过getAttribute(name)将数据或到

package ServletContextTest;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import util.ConnectTool;

public class ServletContextLTest implements ServletContextListener{

	public void contextDestroyed(ServletContextEvent sce) {
	System.out.println("this is last destroyeed");
	
		
	}

	public void contextInitialized(ServletContextEvent sce) {
		ServletContext sct=sce.getServletContext();
		Map<Integer,String> depts=new HashMap<Integer,String>();
		Connection connection=null;
		PreparedStatement pstm=null;
		ResultSet rs=null;
		
		try{
			connection=ConnectTool.getConnection();
			String sql="select deptNo,dname from dept";
			pstm=connection.prepareStatement(sql);
			rs=pstm.executeQuery();
			
			/*put the data into the deptNames */
			while(rs.next()){
				depts.put(rs.getInt(1), rs.getString(2));
			}
			
			sct.setAttribute("dept", depts);
			System.out.println("======listener test is beginning============================");
			
		}catch(Exception e){
			e.printStackTrace();
		}finally{
			ConnectTool.releasersc(rs, pstm, connection);
			
		}
		
	}

}

在配置文件中加入

 <listener>
  <listener-class>ServletContextTest.ServletContextLTest</listener-class>
  </listener>

这样监视器就设置好了
以下通用应用调用上面的数据

package ServletContextTest;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.*;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class CreateEmployee extends HttpServlet{

	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		
		ServletContext sct=getServletConfig().getServletContext();
		Map<Integer,String> dept=(Map<Integer,String>)sct.getAttribute("dept");
		Set<Integer> key=dept.keySet();
		
		response.setContentType("text/html;charset=utf-8");
		PrintWriter out=response.getWriter();
		
		out.println("<html>");
		out.println("<body>");
		out.println("<form action='/register' action='post'>");
		out.println("<table alignb='center'>");
		
		out.println("<tr>");
		out.println("<td>");
		out.println("username:");
		out.println("</td>");
		out.println("<td>");
		out.println("<input type='text' name='username'");
		out.println("</tr>");
		
		out.println("<tr>");
		out.println("<td>");
		out.println("city:");
		out.println("</td>");
		out.println("<td>");
		out.println("<select name='dept'");
		for(Integer i:key){
			out.println("<option value='"+i+"'>"+dept.get(i)+"</option>");
		}
		out.println("</select>");
		out.println("</td>");
		out.println("<tr>");
		
		out.println("</table>");
		out.println("</form>");
		out.println("</body>");
		out.println("</html>");
		out.flush();
	}
	
}

Session和request也可以设置相应的监视器来处理数据

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