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PreservingFileWriter.javaAPI DocGlassfish v2 API3386Wed Aug 30 15:34:10 BST 2006persistence.antlr

PreservingFileWriter

public class PreservingFileWriter extends FileWriter
PreservingFileWriter only overwrites target if the new file is different. Mainly added in order to prevent big and unnecessary recompiles in C++ projects. I/O is buffered.

Fields Summary
protected File
target_file
protected File
tmp_file
Constructors Summary
public PreservingFileWriter(String file)

		super(file+".antlr.tmp");

		// set up File thingy for target..
		target_file = new File(file);

		String parentdirname = target_file.getParent();
		if( parentdirname != null )
	    {
			File parentdir = new File(parentdirname);

			if (!parentdir.exists())
				throw new IOException("destination directory of '"+file+"' doesn't exist");
			if (!parentdir.canWrite())
				throw new IOException("destination directory of '"+file+"' isn't writeable");
		}
		if( target_file.exists() && ! target_file.canWrite() )
			throw new IOException("cannot write to '"+file+"'");

		// and for the temp file
		tmp_file = new File(file+".antlr.tmp");
		// have it nuked at exit
		// RK: this is broken on java 1.4 and
		// is not compatible with java 1.1 (which is a big problem I'm told :) )
		// sigh. Any real language would do this in a destructor ;) ;)
		// tmp_file.deleteOnExit();
Methods Summary
public voidclose()
Close the file and see if the actual target is different if so the target file is overwritten by the copy. If not we do nothing

		Reader source = null;
		Writer target = null;

		try {
			// close the tmp file so we can access it safely...
			super.close();

			char[] buffer = new char[1024];
			int cnt;

			// target_file != tmp_file so we have to compare and move it..
			if( target_file.length() == tmp_file.length() )
			{
				// Do expensive read'n'compare
				Reader tmp;
				char[] buf2 = new char[1024];

				source = new BufferedReader(new FileReader(tmp_file));
				tmp = new BufferedReader(new FileReader(target_file));
				int cnt1, cnt2;
				boolean equal = true;

				while( equal )
				{
					cnt1 = source.read(buffer,0,1024);
					cnt2 = tmp.read(buf2,0,1024);
					if( cnt1 != cnt2 )
					{
						equal = false;
						break;
					}
					if( cnt1 == -1 )		// EOF
						break;
					for( int i = 0; i < cnt1; i++ )
					{
						if( buffer[i] != buf2[i] )
						{
							equal = false;
							break;
						}
					}
				}
				// clean up...
				source.close();
				tmp.close();

				source = tmp = null;

				if( equal )
					return;
			}

			source = new BufferedReader(new FileReader(tmp_file));
			target = new BufferedWriter(new FileWriter(target_file));

			while(true)
			{
				cnt = source.read(buffer,0,1024);
				if( cnt == -1 )
					break;
				target.write(buffer, 0, cnt );
			}
		}
		finally {
			if( source != null )
			{
				try { source.close(); }
				catch( IOException e ) { ; }
			}
			if( target != null )
			{
				try { target.close(); }
				catch( IOException e ) { ;	}
			}
			// RK: Now if I'm correct this should be called anytime.
			if( tmp_file != null && tmp_file.exists() )
			{
				tmp_file.delete();
				tmp_file = null;
			}
		}