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我已经创建了一个运行 sql 查询的 jsp 页面。每次刷新页面时，都会创建一个新的活动会话，因此在达到最大活动会话后，数据库连接丢失，并显示以下错误：

java.sql.SQLException：侦听器拒绝连接并出现以下错误：ORA-12519，TNS：找不到合适的服务处理程序

如何阻止会话的增加。

jsp页面：

   <%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ page import="dao.Dao" %>
<%@ page import="model.Chat_model" %>
<%@ page import="java.util.*" %>
<%@ page import="model.Register_model" %>
  <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"    "http://www.w3.org/TR/html4/loose.dtd">
    <html>
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
     <title>Insert title here</title>
    </head>
      <body>
     <table>
     <%

     Dao object=new Dao();

      ArrayList<Chat_model> a=new ArrayList<Chat_model>();

      String email1=(String)session.getAttribute("email1");
      a=object.selectChat(email1, ((Register_model)(session.getAttribute("user"))).getEmail());

     String name1=(String)session.getAttribute("name1");
     String email2=((Register_model)(session.getAttribute("user"))).getEmail();
     String name2=((Register_model)(session.getAttribute("user"))).getName();
     for(Chat_model k:a)
     {
if(email1.equals(k.getEmail1()))
{
    out.println("<tr><td><b><u>"+name1+"</u>:</b></td><td>"+k.getChat()+"</td> </tr>");
}
else
{
    out.println("<tr><td><b><u>"+name2+"</u>:</b></td><td>"+k.getChat()+"</td><tr>");
}
    }









       %>


       </table>

         <form action="../Controller" method="post">
         <textarea name="chatbox" rows="4" cols="50"></textarea>
           <input type="hidden" name="action" value="chatsend"></input>
           <input type="submit" value="Send"></input>



           </form>
            </body>
            </html>

数据库事务方法：

          public ArrayList<Chat_model> selectChat(String s1,String s2)
  {
    DatabaseConnection db=new DatabaseConnection();
    Connection conn=db.getConnection1();
    Statement stmt = null;


    String email1 = null;
    String chat=null;

    ArrayList<Chat_model> a=new ArrayList<Chat_model>();
    try
    {
        stmt = conn.createStatement();


        String sql = "SELECT email1,chat FROM chat_all where email1="+"'"+s1+"' AND email2="+"'"+s2+"' OR email1="+"'"+s2+"' AND email2="+"'"+s1+"' order by tm_stamp";
        ResultSet rs = stmt.executeQuery(sql);

        while(rs.next()){

            Chat_model object=new Chat_model();


             email1=rs.getString("email1");
             chat=rs.getString("chat");
             object.setEmail1(email1);
             object.setChat(chat);

             a.add(object);



          }


    }

    catch(Exception e)
    {
    e.getStackTrace();  
    }

      return a;
}

数据库连接类：

        public class DatabaseConnection {

String driver = "oracle.jdbc.driver.OracleDriver";
String url = "jdbc:oracle:thin:@siddhartha-PC:1521:xe";
String username = "system";
String password = "password";

Connection conn = null;
public Connection getConnection1(){

    try {
        Class.forName(driver);
    } catch (ClassNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    try {
        conn = DriverManager.getConnection(url,username,password);
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    return conn;
}

public boolean closeConnection(Connection conn){

    try {
        conn.close();
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    return true;
   }
       }
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