Stuck thread in server

Question

My java class is this

package com.indiabulls.portfoliotracker.dao;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import com.indiabulls.trade.dbConnection.JDBCConnection;


public class AppKeyValidationDao {
private static  JDBCConnection instance;
private static  Connection con;
private static  PreparedStatement pstmntAppKeyValidate = null;
private static long lastAccess;
private static Statement stmt = null;

private static String strappKeyValidate = "select count(1) from tablename";

static {
    try {
        instance = new JDBCConnection();
        con = instance.getConnection();
        pstmntAppKeyValidate = con.prepareStatement(strappKeyValidate);
        lastAccess = System.currentTimeMillis();
    } catch (SQLException e) {
    }
}

/**
 * 
 * @param userId
 * @param AppKey
 * @return this method will used for validate app Key from the database
 * @throws SQLException
 */
public static  String validateAppKey(String userId, String AppKey) throws SQLException {
    String status = "false";
    int count = 0;
    ResultSet rs = null;

    try {
        checkConnection();
        pstmntAppKeyValidate.setString(1, userId.trim());
        pstmntAppKeyValidate.setString(2, AppKey.trim());
        rs = pstmntAppKeyValidate.executeQuery();
        if (rs != null) {
            while (rs.next()) {
                count = rs.getInt(1);
            }
        }
        if (count > 0) {
            status = "true";
        }

    } catch (Exception e) {
        status = "ERROR";
        System.out.println("***********************Exception is*******" + e.getMessage());
        e.printStackTrace();
    } finally {
        try {
            if (rs != null) {
                rs.close();
                rs = null;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    return status;

}

/*public static String validateAppKey(String userId, String AppKey) {
    String status = "false";
    int count = 0;
    ResultSet rs = null;
    JDBCConnection instance = null;
    PreparedStatement pstmntAppKeyValidate = null;
    try {
        instance = new JDBCConnection();
    } catch (SQLException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }
     Connection con = instance.getConnection();

    String query = "select count(1) from users_login_details where uld_entity_id = ? and uld_app_key = ? and trunc(uld_current_login_time) >= trunc(sysdate) and uld_invalid_login_flag in ('Y', 'C')";
    try {
         pstmntAppKeyValidate = con.prepareStatement(query);

        pstmntAppKeyValidate.setString(1, userId.trim());
        pstmntAppKeyValidate.setString(2, AppKey.trim());
        rs = pstmntAppKeyValidate.executeQuery();
        if (rs != null) {
            while (rs.next()) {
                count = rs.getInt(1);
            }
        }
        if (count > 0) {
            status = "true";
        }
    } catch (SQLException e) {
        status = "ERROR";
        System.out.println("***********************Exception is*******" + e.getMessage());
        e.printStackTrace();
    } finally {
        try {
            if(rs != null) {
                rs.close();
            }
            if(pstmntAppKeyValidate != null) {
                pstmntAppKeyValidate.close();
            }
            if(con != null) {
                con.close();
            }   
        }catch(Exception e) {
            e.printStackTrace();
        }

    }

    return status;
}*/

private static synchronized void checkConnection() {
    try {
        if ((System.currentTimeMillis() - lastAccess) >= 120000) {
            stmt = con.createStatement();
        }
    } catch (Exception g) {
        try {
            // instance = new JDBCConnection();
            con = instance.getConnection();
            pstmntAppKeyValidate = con.prepareStatement(strappKeyValidate);
            // lastAccess = System.currentTimeMillis();
        } catch (Exception m) {
        }
    }
    lastAccess = System.currentTimeMillis();
}


 }

I am getting stuck thread message on production when there were multiple users . is it good to make synchronized validateAppKey method instead of instance method ?

Answer 1

This problem can be solved by using thread safety (i.e synchronized method )

Answer 2

Remove static on validateAppKey method because it causes the lock on class level.