一種比較簡陋的方法：
?1?ActionListener?taskPerformer?=?new?ActionListener()?{
?2?????????????public?void?actionPerformed(ActionEvent?evt)?{
?3?????????????????log.info("monitor?is?running?at?"?+?new?java.util.Date());
?4?????????????????String?configfile?=?(String)getServletContext().getAttribute("configfile");
?5?????????????????if(configfile?!=?null?&&?configfile.length()!=0){
?6?????????????????????try{
?7?????????????????????????File?file?=?new?File(configfile);
?8?????????????????????????if(file.lastModified()?>?lastModifyTime){
?9?????????????????????????????lastModifyTime?=?file.lastModified();
10?????????????????????????????loadProp();
11?????????????????????????}
12?????????????????????}catch(Exception?e){
13?????????????????????????log.error("construct?file:"?+?configfile?+?"?exception");
14?????????????????????????e.printStackTrace();
15?????????????????????}
16?????????????????}
17?????????????}
18? };
19?????????
20? //啟動監聽線程
21?new?Timer(delay,?taskPerformer).start();
來自geosoft.no的解決方法：
?1?import?java.io.File;
?2?
?3?/**
?4??*?Interface?for?listening?to?disk?file?changes.
?5??*?@see?FileMonitor
?6??*?
?7??*?@author?<a?href="mailto:jacob.dreyer@geosoft.no">Jacob?Dreyer</a>
?8??*/???
?9?public?interface?FileListener
10?{
11???/**
12????*?Called?when?one?of?the?monitored?files?are?created,?deleted
13????*?or?modified.
14????*?
15????*?@param?file??File?which?has?been?changed.
16????*/
17???void?fileChanged?(File?file);
18?}
??1?import?java.util.*;
??2?import?java.io.File;
??3?import?java.lang.ref.WeakReference;
??4?
??5?/**
??6??*?Class?for?monitoring?changes?in?disk?files.
??7??*?Usage:
??8??*
??9??*????1.?Implement?the?FileListener?interface.
?10??*????2.?Create?a?FileMonitor?instance.
?11??*????3.?Add?the?file(s)/directory(ies)?to?listen?for.
?12??*
?13??*?fileChanged()?will?be?called?when?a?monitored?file?is?created,
?14??*?deleted?or?its?modified?time?changes.
?15??*
?16??*?@author?<a?href="mailto:jacob.dreyer@geosoft.no">Jacob?Dreyer</a>
?17??*/???
?18?public?class?FileMonitor
?19?{
?20???private?Timer???????timer_;
?21???private?HashMap?????files_;???????//?File?->?Long
?22???private?Collection??listeners_;???//?of?WeakReference(FileListener)
?23????
?24?
?25???/**
?26????*?Create?a?file?monitor?instance?with?specified?polling?interval.
?27????*?
?28????*?@param?pollingInterval??Polling?interval?in?milli?seconds.
?29????*/
?30???public?FileMonitor?(long?pollingInterval)
?31???{
?32?????files_?????=?new?HashMap();
?33?????listeners_?=?new?ArrayList();
?34?
?35?????timer_?=?new?Timer?(true);
?36?????timer_.schedule?(new?FileMonitorNotifier(),?0,?pollingInterval);
?37???}
?38?
?39?
?40???
?41???/**
?42????*?Stop?the?file?monitor?polling.
?43????*/
?44???public?void?stop()
?45???{
?46?????timer_.cancel();
?47???}
?48???
?49?
?50???/**
?51????*?Add?file?to?listen?for.?File?may?be?any?java.io.File?(including?a
?52????*?directory)?and?may?well?be?a?non-existing?file?in?the?case?where?the
?53????*?creating?of?the?file?is?to?be?trepped.
?54????*?<p>
?55????*?More?than?one?file?can?be?listened?for.?When?the?specified?file?is
?56????*?created,?modified?or?deleted,?listeners?are?notified.
?57????*?
?58????*?@param?file??File?to?listen?for.
?59????*/
?60???public?void?addFile?(File?file)
?61???{
?62?????if?(!files_.containsKey?(file))?{
?63???????long?modifiedTime?=?file.exists()???file.lastModified()?:?-1;
?64???????files_.put?(file,?new?Long?(modifiedTime));
?65?????}
?66???}
?67?
?68???
?69?
?70???/**
?71????*?Remove?specified?file?for?listening.
?72????*?
?73????*?@param?file??File?to?remove.
?74????*/
?75???public?void?removeFile?(File?file)
?76???{
?77?????files_.remove?(file);
?78???}
?79?
?80?
?81???
?82???/**
?83????*?Add?listener?to?this?file?monitor.
?84????*?
?85????*?@param?fileListener??Listener?to?add.
?86????*/
?87???public?void?addListener?(FileListener?fileListener)
?88???{
?89?????//?Don't?add?if?its?already?there
?90?????for?(Iterator?i?=?listeners_.iterator();?i.hasNext();?)?{
?91???????WeakReference?reference?=?(WeakReference)?i.next();
?92???????FileListener?listener?=?(FileListener)?reference.get();
?93???????if?(listener?==?fileListener)
?94?????????return;
?95?????}
?96?
?97?????//?Use?WeakReference?to?avoid?memory?leak?if?this?becomes?the
?98?????//?sole?reference?to?the?object.
?99?????listeners_.add?(new?WeakReference?(fileListener));
100???}
101?
102?
103???
104???/**
105????*?Remove?listener?from?this?file?monitor.
106????*?
107????*?@param?fileListener??Listener?to?remove.
108????*/
109???public?void?removeListener?(FileListener?fileListener)
110???{
111?????for?(Iterator?i?=?listeners_.iterator();?i.hasNext();?)?{
112???????WeakReference?reference?=?(WeakReference)?i.next();
113???????FileListener?listener?=?(FileListener)?reference.get();
114???????if?(listener?==?fileListener)?{
115?????????i.remove();
116?????????break;
117???????}
118?????}
119???}
120?
121?
122???
123???/**
124????*?This?is?the?timer?thread?which?is?executed?every?n?milliseconds
125????*?according?to?the?setting?of?the?file?monitor.?It?investigates?the
126????*?file?in?question?and?notify?listeners?if?changed.
127????*/
128???private?class?FileMonitorNotifier?extends?TimerTask
129???{
130?????public?void?run()
131?????{
132???????//?Loop?over?the?registered?files?and?see?which?have?changed.
133???????//?Use?a?copy?of?the?list?in?case?listener?wants?to?alter?the
134???????//?list?within?its?fileChanged?method.
135???????Collection?files?=?new?ArrayList?(files_.keySet());
136???????
137???????for?(Iterator?i?=?files.iterator();?i.hasNext();?)?{
138?????????File?file?=?(File)?i.next();
139?????????long?lastModifiedTime?=?((Long)?files_.get?(file)).longValue();
140?????????long?newModifiedTime??=?file.exists()???file.lastModified()?:?-1;
141?
142?????????//?Chek?if?file?has?changed
143?????????if?(newModifiedTime?!=?lastModifiedTime)?{
144?
145???????????//?Register?new?modified?time
146???????????files_.put?(file,?new?Long?(newModifiedTime));
147?
148???????????//?Notify?listeners
149???????????for?(Iterator?j?=?listeners_.iterator();?j.hasNext();?)?{
150?????????????WeakReference?reference?=?(WeakReference)?j.next();
151?????????????FileListener?listener?=?(FileListener)?reference.get();
152?
153?????????????//?Remove?from?list?if?the?back-end?object?has?been?GC'd
154?????????????if?(listener?==?null)
155???????????????j.remove();
156?????????????else
157???????????????listener.fileChanged?(file);
158???????????}
159?????????}
160???????}
161?????}
162???}
163?
164?
165???/**
166????*?Test?this?class.
167????*?
168????*?@param?args??Not?used.
169????*/
170???public?static?void?main?(String?args[])
171???{
172?????//?Create?the?monitor
173?????FileMonitor?monitor?=?new?FileMonitor?(1000);
174?
175?????//?Add?some?files?to?listen?for
176?????monitor.addFile?(new?File?("D:\\myjava\\JCreatorWorkspace\\FileMonitor\\test.txt"));
177?
178?????//?Add?a?dummy?listener
179?????monitor.addListener?(monitor.new?TestListener());
180?
181?????//?Avoid?program?exit
182?????while?(!false)?;
183???}
184?
185???
186???private?class?TestListener
187?????implements?FileListener
188???{
189?????public?void?fileChanged?(File?file)
190?????{
191???????System.out.println?("File?["?+?file.getName()?+?"]?changed?At:"?+?new?java.util.Date());
192?????}
193???}
194?}
195?
196?
197?