fsad/assignment4/src/main/java/net/akpain/BooksDatabaseService.java

package net.akpain;/*
 * BooksDatabaseService.java
 *
 * The service threads for the books database server.
 * This class implements the database access service, i.e. opens a JDBC connection
 * to the database, makes and retrieves the query, and sends back the result.
 *
 * author: 2430671
 *
 */

import java.io.*;
//import java.io.OutputStreamWriter;

import java.net.Socket;

import java.util.Arrays;
import java.util.Properties;
import java.util.StringTokenizer;

import java.sql.*;
import javax.sql.rowset.*;
    //Direct import of the classes CachedRowSet and CachedRowSetImpl will fail becuase
    //these clasess are not exported by the module. Instead, one needs to impor
    //javax.sql.rowset.* as above.



public class BooksDatabaseService extends Thread{

    private Socket serviceSocket = null;
    private String[] requestStr  = new String[2]; //One slot for author's name and one for library's name.
    private ResultSet outcome   = null;

	//JDBC connection
    private String USERNAME = Credentials.USERNAME;
    private String PASSWORD = Credentials.PASSWORD;
    private String URL      = Credentials.URL;



    //Class constructor
    public BooksDatabaseService(Socket aSocket){
        serviceSocket = aSocket;
        this.start();
    }


    //Retrieve the request from the socket
    public String[] retrieveRequest()
    {
		StringBuilder sb = new StringBuilder();
        try {
            BufferedReader in = new BufferedReader(new InputStreamReader(serviceSocket.getInputStream()));
            int c = 0;
            while (c != '#') {
                c = in.read();
                if (c == 0) {
                    System.out.println("reading null bytes");
                    System.exit(1);
                }
                sb.append((char) c);
            }
         }catch(IOException e){
            System.out.println("Service thread " + this.getId() + ": " + e);
        }

        String inp = sb.toString();
        this.requestStr = inp.substring(0, inp.length() - 1).split(";");

        // returns [0]: author, [1]: city
        return this.requestStr;
    }


    //Parse the request command and execute the query
    public boolean attendRequest()
    {
        boolean flagRequestAttended = true;
		
		this.outcome = null;
		
		String sql = "select book.title, book.publisher, book.genre, book.rrp, count(*) as \"number_available\" from bookcopy join book on bookcopy.bookid = book.bookid where\n" +
                "\tlibraryid  = (select libraryid from \"library\" where city = ?) and\n" +
                "\tbookcopy.bookid in (select bookid from book where authorid = (select authorid from author where familyname = ?))" +
                // "\t and (onloan = false or onloan is null)\n" +
                "group by book.title, book.publisher, book.genre, book.rrp;";
        // city then author name
		
		try {
			//Connet to the database
            Properties connectionProps = new Properties();
            connectionProps.put("user", USERNAME);
            connectionProps.put("password", PASSWORD);
            Connection conn = DriverManager.getConnection(URL, connectionProps);
			
			//Make the query
			PreparedStatement q = conn.prepareStatement(sql);
            q.setString(1, this.requestStr[1]); // city
            q.setString(2, this.requestStr[0]); // author surname
			
			//Process query
            ResultSet res = q.executeQuery();
            RowSetFactory aFactory = RowSetProvider.newFactory() ;
            CachedRowSet crs = aFactory.createCachedRowSet();
            crs.populate(res);
            outcome = crs;

			//Clean up
			res.close();
            q.close();
            conn.close();
			
		} catch (Exception e)
		{ System.out.println(e); }

        return flagRequestAttended;
    }



    //Wrap and return service outcome
    public void returnServiceOutcome(){
        try {
			//Return outcome
            ObjectOutputStream output = new ObjectOutputStream(serviceSocket.getOutputStream());
            output.writeObject(outcome);
			
            System.out.println("Service thread " + this.getId() + ": Service outcome returned; " + this.outcome);
            
			//Terminating connection of the service socket
			output.close();
            serviceSocket.close();
        }catch (IOException e){
            System.out.println("Service thread " + this.getId() + ": " + e);
        }
    }


    //The service thread run() method
    public void run()
    {
		try {
			System.out.println("\n============================================\n");
            //Retrieve the service request from the socket
            this.retrieveRequest();
            System.out.println("Service thread " + this.getId() + ": Request retrieved: "
						+ "author->" + this.requestStr[0] + "; library->" + this.requestStr[1]);

            //Attend the request
            boolean tmp = this.attendRequest();

            //Send back the outcome of the request
            if (!tmp)
                System.out.println("Service thread " + this.getId() + ": Unable to provide service.");
            this.returnServiceOutcome();

        }catch (Exception e){
            System.out.println("Service thread " + this.getId() + ": " + e);
        }
        //Terminate service thread (by exiting run() method)
        System.out.println("Service thread " + this.getId() + ": Finished service.");
    }

}