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TOVAL comprises a set of java classes for common programming issues. It includes utils for arrays, lists, sets and collections for convenient handling and modification, but also support for mathematic definitions concerning logic (clauses + resolution) together with some algorithms for permutations, powersets and resolution. Additionally it contains a number of types for multisets, matrices with object keys and much more.
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package de.invation.code.toval.file;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.nio.charset.Charset;

import de.invation.code.toval.validate.ParameterException;
import de.invation.code.toval.validate.Validate;
import de.invation.code.toval.validate.ParameterException.ErrorCode;


public class FileWriter {
	
	public static final String DEFAULT_PATH = "";
	public static final String DEFAULT_FILE_NAME = "NewFile";
	public static final String DEFAULT_FILE_EXTENSION = "txt";
	public static final String DEFAULT_EOL_STRING = System.getProperty("line.separator");
	public static final Charset DEFAULT_CHARSET = Charset.forName("UTF-8");
	
	protected String path = getDefaultPath();
	protected String fileName = getDefaultFileName();
	protected Charset charset = DEFAULT_CHARSET;
	protected String eolString = DEFAULT_EOL_STRING;
	protected BufferedWriter output = null;
	protected File outputFile = null;
	protected String fileExtension = DEFAULT_FILE_EXTENSION;
	
	//------- Constructors -------------------------------------------------------------------
	
	/**
	 * Creates a new file writer.

	 * The constructor uses default values for:

	 * file name

	 * path

	 * charset

	 * eol-string

	 * @see #DEFAULT_FILE_NAME
	 * @see #DEFAULT_PATH
	 * @see #DEFAULT_CHARSET
	 * @see #DEFAULT_EOL_STRING
	 */
	public FileWriter() {
		try{
			initialize(getDefaultFileName(), getDefaultPath());
		}catch(ParameterException e){
			// Is only thrown if default path or file names are invalid.
			// Should be avoided by setting the static fields appropriately.
			e.printStackTrace();
		}
	}
	
	/**
	 * Creates a new file writer.

	 * The constructor uses default values for:

	 * path

	 * charset

	 * eol-string

	 * @see #DEFAULT_PATH
	 * @see #DEFAULT_CHARSET
	 * @see #DEFAULT_EOL_STRING
	 * @param fileName The name for the output file.
	 * @throws ParameterException if the file name is null or an empty string.
	 */
	public FileWriter(String fileName) throws ParameterException {
		initialize(fileName, getDefaultPath());
	}
	
	/**
	 * Creates a new file writer.

	 * The constructor uses default values for:

	 * charset

	 * eol-string

	 * @see #DEFAULT_CHARSET
	 * @see #DEFAULT_EOL_STRING
	 * @param path The path for the output file.
	 * @param fileName The name for the output file.
	 * @throws ParameterException if some parameters are null, 

	 * the file path is not a directory or the file name is an empty string.
	 */
	public FileWriter(String path, String fileName) throws ParameterException{
		initialize(fileName, path);
	}
	
	/**
	 * Creates an new file writer.

	 * The constructor uses default values for:

	 * file name

	 * path

	 * eol-string

	 * @see #DEFAULT_FILE_NAME
	 * @see #DEFAULT_PATH
	 * @see #DEFAULT_EOL_STRING
	 * @param charset Charset to use for output file.
	 * @throws ParameterException if the given charset is null.
	 */
	public FileWriter(Charset charset) throws ParameterException{
		setCharset(charset);
		initialize(getDefaultFileName(), getDefaultPath());
	}
	
	/**
	 * Creates a new file writer.

	 * The constructor uses default values for:

	 * path

	 * eol-string

	 * @see #DEFAULT_FILE_NAME
	 * @see #DEFAULT_EOL_STRING
	 * @param fileName The name for the output file.
	 * @param charset Charset to use for output file.
	 * @throws ParameterException if some parameters are null or the file name is an empty string.
	 */
	public FileWriter(String fileName, Charset charset) throws ParameterException {
		setCharset(charset);
		initialize(fileName, getDefaultPath());
	}
	
	/**
	 * Creates a new file writer.

	 * The constructor uses default values for:

	 * eol-string

	 * @see #DEFAULT_EOL_STRING
	 * @param path The path for the output file.
	 * @param fileName The name for the output file.
	 * @param charset Charset to use for output file.
	 * @throws ParameterException if some parameters are null or file name is an empty string.
	 */
	public FileWriter(String path, String fileName, Charset charset) throws ParameterException{
		setCharset(charset);
		initialize(fileName, path);
	}
	
	/**
	 * Creates a new file writer.

	 * The constructor uses default values for:

	 * file name

	 * path

	 * charset

	 * @see #DEFAULT_FILE_NAME
	 * @see #DEFAULT_PATH
	 * @see #DEFAULT_CHARSET
	 * @param eolType
	 * @see EOLType The eol property.
	 * @throws ParameterException if the eolType is null.
	 */
	public FileWriter(EOLType eolType) throws ParameterException{
		this();
		setEOLString(eolType);
	}
	
	/**
	 * Creates a new file writer.

	 * The constructor uses default values for:

	 * path

	 * charset

	 * @see #DEFAULT_PATH
	 * @see #DEFAULT_CHARSET
	 * @param fileName The name for the output file.
	 * @param eolType The eol property.
	 * @throws ParameterException if some parameters are null or the file name is an empty string.
	 */
	public FileWriter(String fileName, EOLType eolType) throws ParameterException {
		this(fileName);
		setEOLString(eolType);
	}
	
	/**
	 * Creates a new file writer.

	 * The constructor uses default values for:

	 * charset

	 * @see #DEFAULT_CHARSET
	 * @param path The path for the output file.
	 * @param fileName The name for the output file.
	 * @param eolType The eol property.
	 * @throws ParameterException if some parameters are null or the file name is an empty string.
	 */
	public FileWriter(String path, String fileName, EOLType eolType) throws ParameterException{
		this(path, fileName);
		setEOLString(eolType);
	}
	
	/**
	 * Creates a new file writer.

	 * The constructor uses default values for:

	 * file name

	 * path

	 * @see #DEFAULT_FILE_NAME
	 * @see #DEFAULT_PATH
	 * @param charset Charset to use for output file.
	 * @param eolType The eol property.
	 * @throws ParameterException if some parameters are null
	 */
	public FileWriter(Charset charset, EOLType eolType) throws ParameterException{
		this(charset);
		setEOLString(eolType);
	}
	
	/**
	 * Creates a new file writer.

	 * The constructor uses default values for:

	 * path

	 * @see #DEFAULT_PATH
	 * @param fileName The name for the output file.
	 * @param charset Charset to use for output file.
	 * @param eolType The eol property.
	 * @throws ParameterException if some parameters are null or the file name is an empty string.
	 */
	public FileWriter(String fileName, Charset charset, EOLType eolType) throws ParameterException {
		this(fileName, charset);
		setEOLString(eolType);
	}
	
	/**
	 * Creates a new file writer.

	 * @param path The path for the output file.
	 * @param fileName The name for the output file.
	 * @param charset Charset to use for output file.
	 * @param eolType The eol property.
	 * @throws ParameterException if some parameters are null or the file name is an empty string.
	 */
	public FileWriter(String path, String fileName, Charset charset, EOLType eolType) throws ParameterException{
		this(path, fileName, charset);
		setEOLString(eolType);
	}
	
	
	//------- Getters and Setters ------------------------------------------------------------
	
	public String getFileName() {
		return String.format("%s%s.%s", getPath(), fileName, getFileExtension());
	}
	
	public String getDefaultFileName(){
		return DEFAULT_FILE_NAME;
	}
	
	public String getPath() {
		return path;
	}
	
	public String getDefaultPath(){
		return DEFAULT_PATH;
	}
	
	public String getFileExtension(){
		return fileExtension;
	}
	
	public void setFileExtension(String extension){
		this.fileExtension = extension;
	}
	
	public String getCharset(){
		return charset.name();
	}
	
	private void setCharset(Charset charset) throws ParameterException{
		Validate.notNull(charset);
		this.charset = charset;
	}
	
	public String getEOLString(){
		return eolString;
	}
	
	protected void setEOLString(EOLType eolType) throws ParameterException{
		Validate.notNull(eolType);
		this.eolString = eolType.toString();
	}
	
	public File getFile(){
		return outputFile;
	}
	
	//------- Methods for setting up the file writer -----------------------------------------
	
	/**
	 * Initializes the file writer with the given file and path names.
	 * @param fileName
	 * @param path
	 * @throws ParameterException if some parameters are null, 

	 * the file path is not a directory or the file name is an empty string.
	 */
	private synchronized void initialize(String fileName, String path) throws ParameterException {
		if(!path.equals(this.path)){
			checkPath(path);
			this.path = path;
		}
		if(!fileName.equals(this.fileName)){
			checkFileName(fileName);
			this.fileName = fileName;
		}
	}

	/**
	 * Sets the path for the file writer where output files are put in.
	 * @param logPath Desired log path.
	 * @throws ParameterException if the given path is null or not a directory.
	 */
	private synchronized void checkPath(String logPath) throws ParameterException {
		Validate.notNull(path);
		File cPath = new File(logPath);
		if(!cPath.exists())
			cPath.mkdirs();
		if(!cPath.isDirectory())
			throw new ParameterException(ErrorCode.INCOMPATIBILITY, logPath + " is not a valid path!");
	}
	
	/**
	 * Sets the name for the output file.
	 * @param fileName Desired file name.
	 * @throws IllegalArgumentException if the given file name is empty.
	 */
	private synchronized void checkFileName(String fileName) throws ParameterException{
		Validate.notNull(fileName);
		File cFile = new File(fileName);
		if(cFile.getName().length()==0)
			throw new ParameterException(ErrorCode.INCOMPATIBILITY, fileName + " is not a valid file-name!");
	}
	
	/**
	 * Creates the output file on the file system.
	 * @throws IOException if the output file is a directory or not writable.
	 */
	private synchronized void prepareFile() throws IOException{
		outputFile = new File(getFileName());
		if(outputFile.exists()) 
			outputFile.delete();
		if(outputFile.isDirectory())
			throw new IOException("I/O Error on creating file: File is a directory!");
		outputFile.createNewFile();
		if(!outputFile.canWrite())
			throw new IOException("I/O Error on creating file: Unable to write into file!");
	}
	
	/**
	 * Creates a buffered writer for writing content into the output file.
	 * @throws IOException if the file cannot be found.
	 */
	private synchronized void prepareWriter() throws IOException{
		output = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(outputFile), charset));
	}
	
	/**
	 * Creates the output file and a buffered writer for filling it with content.
	 * @throws IOException if file or writer could not be created.
	 * @see #prepareFile()
	 * @see #prepareWriter()
	 */
	protected synchronized void prepare() throws IOException{
		if(output == null){
			prepareFile();
			prepareWriter();
		}
	}
	
	
	//------- Functionality ------------------------------------------------------------------
	
	public synchronized void write(Object obj) throws IOException{
		prepare();
		output.write(obj.toString());
	}
	
	public synchronized void writeLine(Object obj) throws IOException{
		prepare();
		output.write(obj.toString());
		output.write(eolString);
		output.flush();
	}
	
	public synchronized void newLine() throws IOException{
		prepare();
		output.newLine();
		output.flush();
	}
	
	public synchronized void closeFile() throws IOException {
		if(output != null){
			output.close();
		}
	}

}