File Deletion, and problems with overwriting instead of adding to file.

[Ben Robertson]

Hey guys, I was gonna put this in the I/O forum, but because i'm pretty new to Java I figured this might actually just be a rookie mistake i'm making and be better suited here, either way, I would really appreciate some help on this:

I am currently writing an IRC bot, originally just for practicing and learning Java, but I am now adding more and more complex functions to it every day, however this latest idea of mine seems to have led me to a brick wall, I was troubleshooting this on my own for four hours last night and it feels like <- that.

The function I am adding is a way to send offline messages to people via a '.pm username: message' command, when you send the command the bot writes a load of stuff to an external .txt, and in my onJoin() method it searches that .txt file for the person who has joined, and if they have been sent a message, will inform them they have new messages. The person then types '.get' and the message is queried to them.

All of this, so far, works, but with the following issues, that I guess I am too inexperienced to work out:

1) When writing the .pm information to the pmList.txt it will only write on the first line, therefore overwriting the last .pm added

2) The pm information needs to be removed from the pmList.txt after they have recieved it, so they don't recieve it every time they join.

Now, I like to find things out for myself before asking people I don't know, so I searched around, and found the best way to handle the removal of the message details from the list, is to have a temp.txt, and write everything in pmList.txt to temp.txt UNLESS it matches the message which was recieved, then delete pmList.txt and rename temp.txt to pmList.txt, this sounded fair enough to me, and the source examples I found made sense, so I set about doing that. But it didnt work. I tried a few different ways of doing it, and none of that worked either, it wasn't deleting or renaming anything. After that I discovered that it is also overwriting the first line of temp.txt with every line of pmList.txt (manually added for testing) instead of adding them, so temp.txt only ever contained the last line of pmList.txt

The following has had commentlines added so you can follow my (probably flawed) logic flow, and again I would really appreciate help with this, this feature is so close to completion, I just need this to work correctly.

/**
*All of the below takes place inside the onMessage() method which is native to PircBot API
*The first part writes the command(and appends the sender for later use)to pmList.txt
*The second is for delivery and removal of the message after deliver (or not, as the case may be)
**/

if(message.startsWith(".pm")&&message.substring(3).startsWith(" ")){
				try{
					FileWriter pmList = new FileWriter("pmList.txt");
					BufferedWriter out = new BufferedWriter(pmList);
					FileInputStream file=new FileInputStream("pmList.txt");
					DataInputStream in = new DataInputStream(file);
					BufferedReader br = new BufferedReader(new InputStreamReader(in));
                   /** 
					*Presumably this is the part which is overwriting the first line rather than adding a new line
					* this works as I thought it would apart from that slight detail :P
					**/
					if(br.readLine()==null);{
						out.write(message+"~"+sender);
						out.close();
					}
				}
				catch(Exception e){
					sendNotice("Bottleskup", Colors.BLUE+"***[TTW]*** Error writing to files");
				}
			}

/**
 *End of writer
 **/

			if (message.startsWith(".get")){
				try{
					FileInputStream file=new FileInputStream("pmList.txt");
					File xfile = new File("pmList.txt");
					DataInputStream in = new DataInputStream(file);
					BufferedReader br = new BufferedReader(new InputStreamReader(in));
					String fullCmd;
					while((fullCmd=br.readLine())!=null){
						/**
						 * if the line it is reading contains the person who sent the .get message
						 * the whole message (which looks like '.pm user: message~sender'
						 * is split up to get the user, message and sender saved as String target, msg and source respectively
						 * The message is then queried to the sender
						 * 
						 * The else{} section is my latest attempt at getting it to remove the line once it has been sent
						 * the theory is that if the line doesnt contain the person who sent '.get' then it is written to
						 * the tempfile, pmList is then deleted and tempfile renamed.
						 * 
						 * Doesnt work though...
						 **/
						if(fullCmd.contains(sender)){
							String[] splitCmd=fullCmd.split(":");
							String[] storeTarg=splitCmd[0].split(" ");
							String[] storeMsg=splitCmd[1].split("~");
							String msg=storeMsg[0];
							String source=storeMsg[1];
							String target=storeTarg[1];
							sendMessage(target, Colors.BLUE+"***[TTW MAIL]*** New message from "+Colors.BLACK+source.toUpperCase()
									+Colors.NORMAL+Colors.BLACK+": " + msg);
						}
						else{
							/** 
							 * This works to the extent that it does make the temp file
							 * and it does write to it
							 * however it also overwrites rather than adding, and deletion and renaming doesnt work at all...
							 */
							File tempFile = new File("TempFile.txt");
							BufferedWriter out = new BufferedWriter(new FileWriter(tempFile));
							out.write(fullCmd);
							out.newLine();
							out.close();
							boolean success=xfile.delete();
							if(success){
								sendNotice("Bottleskup", "file deleted");
							}
							else{
								sendNotice("Bottleskup", "file not deleted");
								xfile.delete();
							}
							boolean renamesuccess=tempFile.renameTo(xfile);
							if(renamesuccess){
								sendNotice("Bottleskup", "file renamed");
							}
							else{
								sendNotice("Bottleskup", "file not renamed");
								tempFile.renameTo(xfile);
							}
						}
					}
				}
				
				catch(Exception e){
				}
			}	

Any comments are appreciated

EDIT: the file.delete() and file.renameTo() methods inside my 'failed to delete' and 'failed to rename' sections are just me being cheeky and saying 'ok if you fail to delete the file, delete the file', but to no avail. Long shot really.

[Rob Spoor]

FileWriter pmList = new FileWriter("pmList.txt");   
BufferedWriter out = new BufferedWriter(pmList);   
FileInputStream file=new FileInputStream("pmList.txt");   
DataInputStream in = new DataInputStream(file);   
BufferedReader br = new BufferedReader(new InputStreamReader(in));   
/**   
 *Presumably this is the part which is overwriting the first line rather than adding a new line  
 * this works as I thought it would apart from that slight detail :P  
 **/   
if(br.readLine()==null);{   
    out.write(message+"~"+sender);   
    out.close();   
} 

Very important: that ; after the if shouldn't be there. It causes the next block to be executed always; after all, the ; is now the body of the if-statement.
Also, the DataInputStream is unnecessary as the InputStreamReader doesn't use any of its, only those of InputStream.

When you create a new FileWriter like this it will clear the current contents. Use one of the other constructors, with a boolean, to make it append instead.

You are here trying to write to the same file as you're reading from. That's not going to work, period. You'd need to write to a temp file.

You only close the BufferedReader around pmList.txt when there's nothing more to read (well, if that ; is removed). You never close the BufferedReader though. As a result, pmList.txt will always have an open FileInputStream, and therefore the file is always busy. That's why the deletion of this file fails. And because the file still exists when you try to rename to it, the renaming fails as well.

[Ben Robertson]

Rob Spoor wrote:Very important: that ; after the if

jeeeez, I didnt even see that, thanks for pointing that out.

I guess it makes sense that you cant write to something you are reading, and I understand what you have said about the input stream always being busy so it cant delete and therefore rename. My bad.

That's cleared things up a bit, it doesnt work yet, but I'm gonna go study Javadoc reading writing and i/o streams a bit closer, i'm obviously implementing things incorrectly.

Thanks again for your help

[Rob Spoor]

You're welcome

[Campbell Ritchie]

Ben Robertson wrote: . . . i/o streams . . .

. . . in which case you won't want to read about I/O Streams with capital letters