server/Logger/FileLog.java

import java.util.Date;
import java.text.DateFormat;
import java.util.Locale;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

/**
 * FileLog <br> <br>
 * 
 * The FileLog class is an implementation of the Log interface, and as the
 * name suggest writes all output to a file. The filename is specified
 * during construction, and there is no default for a no-arg constructor.
 * Various checks are carried out to check that writing will be possible and
 * an IOException is thrown if for some reason it fails. If the file exists
 * then the write() method will append to it. <br> <br>
 * 
 * Revision History: <br>
 * 1.8 - Added a fix to the write() method to ensure log is synchronised correctly [28/04/00] <br>
 * 1.7 - Added suspend() and resume() methods [26/04/00] <br>
 * 1.6 - Added open() method so that a new log file can be opened after a close() [26/04/00] <br>
 * 1.5 - Made sure writing cannot be attempted when logfile not open [26/04/00] <br>
 * 1.4 - Method of clearing the logfile improved [26/04/00] <br>
 * 1.3 - Improved javadoc comments and tidied up [26/04/00] <br>
 * 1.2 - Used the .newLine() method to write a new line, rather than \n [14/04/00] <br>
 * 1.1 - Used an interface to create seperate File & Screen logs [15/03/00] <br>
 * 1.0 - Original File-only version <br>
 * 
 * @author T.D.Bishop [tdb1@ukc.ac.uk]
 * @version 1.8, 28/04/2000
 */
public class FileLog implements Log {
    
        /**
         * This attribute is used by the Server class to print out versions
         * of all class files that form the server on startup.
         */
    public static String version = "1.8, 28/04/2000";
    
        /**
         * The constructor checks that writing will be ok, then sets up the
         * writer. It makes use of the fileCheck() method found later on to
         * ensure writing will be ok, and throws an IOException if there is
         * a problem. Errors at this stage cannot be logged because the
         * logging mechanism has not be setup completely, so any problems
         * are printed to the screen in the same format used for logging.
         * 
         * @param filename The filename to which logging should be written.
         * @throws IOException if there is a problem with the file check.
         */
    public FileLog(String filename) throws IOException{
        this.filename = filename;
                // Perform file check to make sure writing is ok
        if(!fileCheck()){
                        // Have to system.out.println errors because logging mechanism failed !
            System.out.println(formatLogLine(this, "File check failed, construction terminated"));
            throw new IOException("File check failed, unable to create FileLog");
        }
        try{
                        // Setup the writer
            writer = new BufferedWriter(new FileWriter(filename, true));
                        // File is now open
                        open = true;
        }
        catch(IOException e){
            System.out.println(formatLogLine(this, "Attemp to setup writer failed: "+e.getMessage()));
        }
                // Put an initial line into the log
        write(this, "Logging initialised");
    }
    
        /**
         * The write() method writes a line of log to the file, prepending
         * it with some information about where to line came from and the
         * date. This formatting is handled by the formatLogLine() method.
         * There is some synchronisation here due to problems with the logfiles
         * having multiple lines written on the same line, followed by dotted
         * newlines in the wrong places. This is due to this method being
         * called by multiple threads.
         * 
         * @param source A reference to the source of the message.
         * @param input The message to be logged.
         */
    public void write(Object source, String input){
                // Check to make sure file is open
                if(open){
                        // Produce a nicely formatted line for the logfile
                        String line = formatLogLine(source, input);
                        try{
                                // We have to synchronize here due to problems with two write()'s being called before a newLine()
                                synchronized(writer){
                                        // Attempt to write the line
                                        writer.write(line);
                                        // Best to use newLine() as it will use the correct platform encoding
                                        writer.newLine();
                                }
                                // Make sure the line is written immeidiately
                                writer.flush();
                        }
                        catch(IOException e){
                                // We'd best log the error
                        System.out.println(formatLogLine(this, "Writing to logfile failed: "+e.getMessage()));
                                // As it's an IOException we should suspend logging
                                open = false;
                }
                }
                else{
                        // If file is not open we should print this to the screen
                        System.out.println(formatLogLine(this, "Write failed: file not open"));
                }
    }
    
        /**
         * This method generates a nicely formatted line for the logfile,
         * including the date/time and the source of the message. The date
         * and time are formatted using the DateFormat class, and the source
         * class is formatted using the toString() method found in every
         * source file for the server. This is then prepended to the message
         * and returned.
         * 
         * @param source A reference to the source of the message.
         * @param input The message to be logged.
         * @return The string to be written to the log.
         */
    private String formatLogLine(Object source, String input){
                // Construct the date string using the DateFormat class
        String date = DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.MEDIUM).format(new Date());
                // Return the date, the toString() of the source and the input
        return "[" + date + "] " + source.toString() + ": " + input;
    }
        
    /**
         * The toString() method returns the name of the Class for formatting
         * when it writes to the logfile. <br>
         * 
         * @return The formatted string identifying this Class.
         */
    public String toString(){
        return this.getClass().getName();
    }
    
        /**
         * The clear() method erases the contents of the logfile. It does
         * this in a very clumsy way - by closing the writer and opening a
         * new one which is set not to append. This results in the logfile
         * being overwritten, which effectively erases it.
         */
    public void clear(){
                // Check file is open
                if(open){
                        write(this, "Attempting to clear logfile");
                        try{
                                // Close appending writer
                                open = false;
                                writer.close();
                                // Open a non-appending writer
                                writer = new BufferedWriter(new FileWriter(filename));
                                open = true;
                        }
                        catch(IOException e){
                                // We'd best log the error
                                write(this, "Attempt to clear logfile failed: "+e.getMessage());
                                // As it's an IOException we should suspend logging
                                open = false;
                        }
                }
                else{
                        // If file is not open we should print this to the screen
                        System.out.println(formatLogLine(this, "Clearing failed: file not open"));
                }
    }
    
        /**
         * The close() method closes the logfile and no more data can be written.
         * If writing is attempted after close() has been called an error will be
         * generated. The open() method can be used to reopen or open a new file.
         */
    public void close(){
                // Check to see if a file is open
                if(open){
                        write(this, "Attempting to terminate logging");
                        try{
                                open = false;
                        writer.close();         
                        }
                        catch(IOException e){
                                write(this, "Attempt to close logfile failed: "+e.getMessage());
                                // As it's an IOException we should suspend logging
                                open = false;
                        }
                }
                else{
                        // If file is not open we should print this to the screen
                        System.out.println(formatLogLine(this, "Close failed: file not open"));
                }
    }
    
        /**
         * The open() method opens a new file after the close() method has
         * been called on the FileLog. This enables the user to easily change
         * the file to which the log is being written. An error is generated
         * if a file is already open.
         * 
         * @param filename The new file to write to.
         * @throws IOException if the file cannot be written to.
         */
        public void open(String filename) throws IOException{
                // Check to see if a file is open
                if(open){
                        // If file is already open then we should log that this went wrong
                        write(this, "Open failed: a file is already open");
                }
                else{
                        this.filename = filename;
                        if(!fileCheck()) {
                                // Have to system.out.println errors because logging mechanism failed !
                                System.out.println(formatLogLine(this, "File check failed, construction terminated"));
                                throw new IOException("File check failed, unable to create FileLog");
                        }
                        try{
                                // Setup the writer
                                writer = new BufferedWriter(new FileWriter(filename, true));
                                // File is now open
                                open = true;
                        }
                        catch(IOException e){
                                System.out.println(formatLogLine(this, "Attempt to open writer failed: "+e.getMessage()));
                        }
                }
        }
        
        /**
         * The suspend() method halts writing to the file by setting the open
         * boolean to false, and thus blocking the write() method. A line is
         * written to the logfile beforehand to note that writing has been
         * suspended.
         */
        public void suspend(){
                // Check to see if a file is open
                if(open){
                        // Make a note of the fact that writing has been suspended
                        write(this, "Writing suspended");
                        // Make sure writing not permitted
                        open=false;
                }
                else{
                        // If file is not open we should print this to the screen
                        System.out.println(formatLogLine(this, "Suspend failed: file not open"));
                }
        }
        
        /**
         * The resume() method resumes writing to the file by setting the open
         * boolean to true. A line is written to the logfile to signify this
         * event occuring.
         */
        public void resume(){
                // Check to see if a file is open
                if(open){
                        // If file is open we should print this to the screen
                        System.out.println(formatLogLine(this, "Resume failed: file open"));
                }
                else{
                        // Permit writing again
                        open=true;
                        // Make a note of the fact that writing has been resumed
                        write(this, "Writing resumed");
                }
        }
        
        /**
         * The fileCheck() method is used to ensure that writing is ok. It
         * performs so basic checks to make sure that if the file exists
         * it can be written to, and if not a new file is created. A boolean
         * result is returned to signify success or failure.
         * 
         * @return A boolean value signify whether the test was sucessful.
         */
    private boolean fileCheck(){
        boolean fileOK = false;
        try{
            File file = new File(filename);
                        
                        // File already exists
            if(file.exists()) {
                /* Only want success if it is a file (not a directory)
                                 * and can be written to.
                                 */
                                if(file.isFile() && file.canWrite()) {
                    fileOK = true;
                }
            }
                        // Create a new file and suceed
            else{
                file.createNewFile();
                fileOK = true;
            }
        }
        catch(IOException e){
            System.out.println(formatLogLine(this, "File check failed: "+e.getMessage()));
        }
        
        return fileOK;
    }
    
        /**
         * The filename of the currently open, or last open, file.
         */
    private String filename;
        
        /**
         * A reference to the writer being used.
         */
    private BufferedWriter writer;
        
        /**
         * A boolean signifying whether a file is open or not.
         */
        private boolean open = false;
    
}
Revision:	1.1
Committed:	Mon Nov 6 21:28:53 2000 UTC (24 years ago) by tdb
Branch:	MAIN
CVS Tags:	PROJECT_COMPLETION, HEAD
Log Message:	File Logging implementation of the logging mechanism interface.
#	User	Rev	Content
1	tdb	1.1	import java.util.Date;
2			import java.text.DateFormat;
3			import java.util.Locale;
4			import java.io.BufferedWriter;
5			import java.io.File;
6			import java.io.FileWriter;
7			import java.io.IOException;
8
9			/**
10			* FileLog <br> <br>
11			*
12			* The FileLog class is an implementation of the Log interface, and as the
13			* name suggest writes all output to a file. The filename is specified
14			* during construction, and there is no default for a no-arg constructor.
15			* Various checks are carried out to check that writing will be possible and
16			* an IOException is thrown if for some reason it fails. If the file exists
17			* then the write() method will append to it. <br> <br>
18			*
19			* Revision History: <br>
20			* 1.8 - Added a fix to the write() method to ensure log is synchronised correctly [28/04/00] <br>
21			* 1.7 - Added suspend() and resume() methods [26/04/00] <br>
22			* 1.6 - Added open() method so that a new log file can be opened after a close() [26/04/00] <br>
23			* 1.5 - Made sure writing cannot be attempted when logfile not open [26/04/00] <br>
24			* 1.4 - Method of clearing the logfile improved [26/04/00] <br>
25			* 1.3 - Improved javadoc comments and tidied up [26/04/00] <br>
26			* 1.2 - Used the .newLine() method to write a new line, rather than \n [14/04/00] <br>
27			* 1.1 - Used an interface to create seperate File & Screen logs [15/03/00] <br>
28			* 1.0 - Original File-only version <br>
29			*
30			* @author T.D.Bishop [tdb1@ukc.ac.uk]
31			* @version 1.8, 28/04/2000
32			*/
33			public class FileLog implements Log {
34
35			/**
36			* This attribute is used by the Server class to print out versions
37			* of all class files that form the server on startup.
38			*/
39			public static String version = "1.8, 28/04/2000";
40
41			/**
42			* The constructor checks that writing will be ok, then sets up the
43			* writer. It makes use of the fileCheck() method found later on to
44			* ensure writing will be ok, and throws an IOException if there is
45			* a problem. Errors at this stage cannot be logged because the
46			* logging mechanism has not be setup completely, so any problems
47			* are printed to the screen in the same format used for logging.
48			*
49			* @param filename The filename to which logging should be written.
50			* @throws IOException if there is a problem with the file check.
51			*/
52			public FileLog(String filename) throws IOException{
53			this.filename = filename;
54			// Perform file check to make sure writing is ok
55			if(!fileCheck()){
56			// Have to system.out.println errors because logging mechanism failed !
57			System.out.println(formatLogLine(this, "File check failed, construction terminated"));
58			throw new IOException("File check failed, unable to create FileLog");
59			}
60			try{
61			// Setup the writer
62			writer = new BufferedWriter(new FileWriter(filename, true));
63			// File is now open
64			open = true;
65			}
66			catch(IOException e){
67			System.out.println(formatLogLine(this, "Attemp to setup writer failed: "+e.getMessage()));
68			}
69			// Put an initial line into the log
70			write(this, "Logging initialised");
71			}
72
73			/**
74			* The write() method writes a line of log to the file, prepending
75			* it with some information about where to line came from and the
76			* date. This formatting is handled by the formatLogLine() method.
77			* There is some synchronisation here due to problems with the logfiles
78			* having multiple lines written on the same line, followed by dotted
79			* newlines in the wrong places. This is due to this method being
80			* called by multiple threads.
81			*
82			* @param source A reference to the source of the message.
83			* @param input The message to be logged.
84			*/
85			public void write(Object source, String input){
86			// Check to make sure file is open
87			if(open){
88			// Produce a nicely formatted line for the logfile
89			String line = formatLogLine(source, input);
90			try{
91			// We have to synchronize here due to problems with two write()'s being called before a newLine()
92			synchronized(writer){
93			// Attempt to write the line
94			writer.write(line);
95			// Best to use newLine() as it will use the correct platform encoding
96			writer.newLine();
97			}
98			// Make sure the line is written immeidiately
99			writer.flush();
100			}
101			catch(IOException e){
102			// We'd best log the error
103			System.out.println(formatLogLine(this, "Writing to logfile failed: "+e.getMessage()));
104			// As it's an IOException we should suspend logging
105			open = false;
106			}
107			}
108			else{
109			// If file is not open we should print this to the screen
110			System.out.println(formatLogLine(this, "Write failed: file not open"));
111			}
112			}
113
114			/**
115			* This method generates a nicely formatted line for the logfile,
116			* including the date/time and the source of the message. The date
117			* and time are formatted using the DateFormat class, and the source
118			* class is formatted using the toString() method found in every
119			* source file for the server. This is then prepended to the message
120			* and returned.
121			*
122			* @param source A reference to the source of the message.
123			* @param input The message to be logged.
124			* @return The string to be written to the log.
125			*/
126			private String formatLogLine(Object source, String input){
127			// Construct the date string using the DateFormat class
128			String date = DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.MEDIUM).format(new Date());
129			// Return the date, the toString() of the source and the input
130			return "[" + date + "] " + source.toString() + ": " + input;
131			}
132
133			/**
134			* The toString() method returns the name of the Class for formatting
135			* when it writes to the logfile. <br>
136			*
137			* @return The formatted string identifying this Class.
138			*/
139			public String toString(){
140			return this.getClass().getName();
141			}
142
143			/**
144			* The clear() method erases the contents of the logfile. It does
145			* this in a very clumsy way - by closing the writer and opening a
146			* new one which is set not to append. This results in the logfile
147			* being overwritten, which effectively erases it.
148			*/
149			public void clear(){
150			// Check file is open
151			if(open){
152			write(this, "Attempting to clear logfile");
153			try{
154			// Close appending writer
155			open = false;
156			writer.close();
157			// Open a non-appending writer
158			writer = new BufferedWriter(new FileWriter(filename));
159			open = true;
160			}
161			catch(IOException e){
162			// We'd best log the error
163			write(this, "Attempt to clear logfile failed: "+e.getMessage());
164			// As it's an IOException we should suspend logging
165			open = false;
166			}
167			}
168			else{
169			// If file is not open we should print this to the screen
170			System.out.println(formatLogLine(this, "Clearing failed: file not open"));
171			}
172			}
173
174			/**
175			* The close() method closes the logfile and no more data can be written.
176			* If writing is attempted after close() has been called an error will be
177			* generated. The open() method can be used to reopen or open a new file.
178			*/
179			public void close(){
180			// Check to see if a file is open
181			if(open){
182			write(this, "Attempting to terminate logging");
183			try{
184			open = false;
185			writer.close();
186			}
187			catch(IOException e){
188			write(this, "Attempt to close logfile failed: "+e.getMessage());
189			// As it's an IOException we should suspend logging
190			open = false;
191			}
192			}
193			else{
194			// If file is not open we should print this to the screen
195			System.out.println(formatLogLine(this, "Close failed: file not open"));
196			}
197			}
198
199			/**
200			* The open() method opens a new file after the close() method has
201			* been called on the FileLog. This enables the user to easily change
202			* the file to which the log is being written. An error is generated
203			* if a file is already open.
204			*
205			* @param filename The new file to write to.
206			* @throws IOException if the file cannot be written to.
207			*/
208			public void open(String filename) throws IOException{
209			// Check to see if a file is open
210			if(open){
211			// If file is already open then we should log that this went wrong
212			write(this, "Open failed: a file is already open");
213			}
214			else{
215			this.filename = filename;
216			if(!fileCheck()) {
217			// Have to system.out.println errors because logging mechanism failed !
218			System.out.println(formatLogLine(this, "File check failed, construction terminated"));
219			throw new IOException("File check failed, unable to create FileLog");
220			}
221			try{
222			// Setup the writer
223			writer = new BufferedWriter(new FileWriter(filename, true));
224			// File is now open
225			open = true;
226			}
227			catch(IOException e){
228			System.out.println(formatLogLine(this, "Attempt to open writer failed: "+e.getMessage()));
229			}
230			}
231			}
232
233			/**
234			* The suspend() method halts writing to the file by setting the open
235			* boolean to false, and thus blocking the write() method. A line is
236			* written to the logfile beforehand to note that writing has been
237			* suspended.
238			*/
239			public void suspend(){
240			// Check to see if a file is open
241			if(open){
242			// Make a note of the fact that writing has been suspended
243			write(this, "Writing suspended");
244			// Make sure writing not permitted
245			open=false;
246			}
247			else{
248			// If file is not open we should print this to the screen
249			System.out.println(formatLogLine(this, "Suspend failed: file not open"));
250			}
251			}
252
253			/**
254			* The resume() method resumes writing to the file by setting the open
255			* boolean to true. A line is written to the logfile to signify this
256			* event occuring.
257			*/
258			public void resume(){
259			// Check to see if a file is open
260			if(open){
261			// If file is open we should print this to the screen
262			System.out.println(formatLogLine(this, "Resume failed: file open"));
263			}
264			else{
265			// Permit writing again
266			open=true;
267			// Make a note of the fact that writing has been resumed
268			write(this, "Writing resumed");
269			}
270			}
271
272			/**
273			* The fileCheck() method is used to ensure that writing is ok. It
274			* performs so basic checks to make sure that if the file exists
275			* it can be written to, and if not a new file is created. A boolean
276			* result is returned to signify success or failure.
277			*
278			* @return A boolean value signify whether the test was sucessful.
279			*/
280			private boolean fileCheck(){
281			boolean fileOK = false;
282			try{
283			File file = new File(filename);
284
285			// File already exists
286			if(file.exists()) {
287			/* Only want success if it is a file (not a directory)
288			* and can be written to.
289			*/
290			if(file.isFile() && file.canWrite()) {
291			fileOK = true;
292			}
293			}
294			// Create a new file and suceed
295			else{
296			file.createNewFile();
297			fileOK = true;
298			}
299			}
300			catch(IOException e){
301			System.out.println(formatLogLine(this, "File check failed: "+e.getMessage()));
302			}
303
304			return fileOK;
305			}
306
307			/**
308			* The filename of the currently open, or last open, file.
309			*/
310			private String filename;
311
312			/**
313			* A reference to the writer being used.
314			*/
315			private BufferedWriter writer;
316
317			/**
318			* A boolean signifying whether a file is open or not.
319			*/
320			private boolean open = false;
321
322			}