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ConnectionPool |
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1 /* 2 * Copyright (c) 1998-2002, The University of Sheffield. 3 * 4 * This file is part of GATE (see http://gate.ac.uk/), and is free 5 * software, licenced under the GNU Library General Public License, 6 * Version 2, June 1991 (in the distribution as file licence.html, 7 * and also available at http://gate.ac.uk/gate/licence.html). 8 * 9 * Atanas Kiryakov, 01/02/2002 10 * 11 * $Id: ConnectionPool.java,v 1.1 2002/02/04 08:12:46 nasso Exp $ 12 */ 13 package gate.persist; 14 15 16 import java.util.*; 17 import java.sql.*; 18 19 /** 20 A generic implementation of pool of references to objects of any kind. 21 It is thread-safe, so, allows multiple users to get and release objects 22 "simultaneously". In fact, the standard Java synchronization is used. 23 <BR><BR> 24 The base idea is that, a calling routine will try to get 25 an object from the pool with method Get. On success, it will use the 26 object and return it in the pool with the method Put. 27 <BR><BR> 28 If there ares no available objects in the pool, Get will return <B>null</B>. 29 Then the calling routine should create a new object. Further, scenario goes 30 in the same way - when finished using the object, calling routine shoud Put 31 it in the pool for future use, instead of leaving it to be garbage-collected. 32 <BR><BR> 33 The pool initially is empty. The only way to increase the number of objects 34 managed by the pool, is some external process to Put an object, that was 35 created, instead of previously Get from the pool. 36 <BR><BR> 37 Pool stores only references to currently "free" or available objects. When 38 some external routine Gets an object from the pool, its reference is not 39 locked, it is simply removed from the pool. 40 */ 41 public class ConnectionPool { 42 private Vector connections; 43 private int size; 44 private String url; 45 private int connCount; 46 47 /** 48 Constructs and object pool with specified size. 49 @param size determines the maximum size of the pool. This is the number 50 free objects that it can manage at the same time 51 */ 52 public ConnectionPool(int size, String url) { 53 this.size = size; 54 connections = new Vector(this.size); 55 this.url = url; 56 this.connCount = 0; 57 } // ConnectionPool 58 59 /** 60 Pulls out an object from the pool. The reference to the object is removed 61 from the pool and their is no longer any kind of relation between this 62 object and the pool. It can be returned back (released) by Put method. 63 @return an object from the pool, if available.<BR> 64 Otherwise, returns <B>null</B> 65 */ 66 public synchronized Connection get() 67 throws SQLException,ClassNotFoundException{ 68 int currAvailable = connections.size(); 69 if (currAvailable > 0){ 70 Connection conn = (Connection) connections.elementAt(currAvailable-1); 71 connections.removeElementAt(currAvailable-1); 72 return conn; 73 } 74 else { 75 if (connCount < size) { 76 Connection newCon = DBHelper.connect(url); 77 connCount++; 78 return newCon; 79 } 80 else { 81 try { 82 wait(); 83 } 84 catch (java.lang.InterruptedException ie) { 85 throw new SQLException(" Thread interrupted while waiting " 86 +"to get Connection from ConnectionPool !"); 87 } 88 return get(); 89 } 90 } 91 } // Get 92 93 /** 94 Puts an object in the pool, those stating that it's "free" or available 95 for use by another processes and routines. An object can be put in the pool, 96 without need to be get from there before. 97 @return <B>true</B> on success<BR> 98 <B>false</B> when the object was not put in the pool, 99 because the maximal number of references in the pool was riched 100 */ 101 public synchronized boolean put(Connection conn){ 102 connections.addElement(conn); 103 notify(); 104 return true; 105 } // Put 106 107 public void finalize() { 108 for (int i = 0; i<connections.size(); i++){ 109 try { 110 DBHelper.disconnect((Connection) connections.elementAt(i)); 111 } 112 catch (Exception e){ 113 e.printStackTrace(); 114 } 115 } 116 } 117 }
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