Files

Text File

Here is the file we'll play with for these examples (with highly imaginative file contents)

Line 1
Line 2
Line 3
Line 4

Read Lines

1. Read all the lines in the file using the "Files" utility method readAllLines
2. The try-catch is typical for many file operations. The compiler will tell you when you need to catch an exception, and you can use a similar try-catch statement.

Here is the output:

------------------
demoReadLinesFromFile
Line Count: 4
Lines Read:
[Line 1, Line 2, Line 3, Line 4]

private void demoReadLinesFromFile()  {
	//
	//Note: Many file methods need exception handling as shown here
	//Assume file "FourLines.txt" is in current (run) directory
	String path = "FourLines.txt";
	List<String> lines = null;

	//UTF_8 preferred over default
	//Charset.defaultCharset());

	#2try {
		lines = #1Files.readAllLines(Paths.get(path), StandardCharsets.UTF_8);
	} catch (IOException exeption) {
		System.out.println("IO exception for -- " + path);
		System.out.println(exeption.getMessage());
	}
	System.out.println("------------------");
	System.out.println("demoReadLinesFromFile");
	System.out.println("Line Count: " + lines.size());
	System.out.println("Lines Read:");
	System.out.println(lines);
}

Read Text

Here we read the entire file contents as a String. The helper method readFile is where the work happens. We open a scanner on the path and read up to the end-of-file marker.

Here is the output:

------------------
demoReadTextFromFile
Text:
Line 1
Line 2
Line 3
Line 4

private void demoReadTextFromFile()  {
	//Here we'll call a helper method
	String
		path = "FourLines.txt",
		text = null;
	try { text = readFile(path);
	} catch (FileNotFoundException exeption) {
		System.out.println("IO exception for -- " + path);
		System.out.println(exeption.getMessage());
	}
	System.out.println("------------------");
	System.out.println("demoReadTextFromFile");
	System.out.println("Text:");
	System.out.println(text);
}

public static String readFile(String path) throws FileNotFoundException  {
	//Helper utility method that reads and returns all text from a file path
	//Note that "\\Z" is a end-of-file character for a text file
	String content = "";
	File file = new File(path);
	Scanner scanner = new Scanner(file);
	scanner.useDelimiter("\\Z");
	if (scanner.hasNext())
		content = scanner.next();
	scanner.close();
	return content;
}

Write Text

Here we write a string to a file.

public static void writeFile(String path , String contents)  {
	try {
		PrintWriter writer = new PrintWriter(path, "UTF-8");
		writer.println(contents);
		writer.close();
	} catch(Exception e) {
		System.out.println("EXCEPTION in writeFile() " + e.toString()); }
}