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Reading Files

There are several ways to read files in Groovy.

Using the File.text property

First, you can simply get the text property of the file.

def file2 = new File('groovy2.txt')
// Using the text property:
file2.text = '''We can even use the text property of
a file to set a complete block of text at once.'''

Using A Writer instance

def file3 = new File('groovy3.txt')
// Using a writer object:
file3.withWriter('UTF-8') { writer ->
    writer.write('We can also use writers to add contents.')
}

Reading Contents into An Array

def file1 = new File('groovy1.txt')
// Reading contents of files to an array:
def lines = file1.readLines()
assert 2 == lines.size()
assert 'Working with files the Groovy way is easy.' == lines[0]
 
// Or we read with the text property:
assert 'We can also use writers to add contents.' == file3.text

Using Reader

def file2 = new File('groovy2.txt')
// Or with a reader:
count = 0
file2.withReader { reader ->
    while (line = reader.readLine()) {
        switch (count) {
            case 0:
                assert 'We can even use the text property of' == line
                break
            case 1:
                assert 'a file to set a complete block of text at once.' == line
                break
        }
        count++
    }
}

Using a Filter

def file1 = new File('groovy1.txt')

// We can also read contents with a filter:
sw = new StringWriter()
file1.filterLine(sw) { it =~ /Groovy/ }
assert 'Working with files the Groovy way is easy.\r\n' == sw.toString()

Retrieving Files

We can look for files in a directory with different methods. For a complete list, see the File GDK documentation.

files = []
new File('.').eachFileMatch(~/^groovy.*\.txt$/) { files << it.name }
assert ['groovy1.txt', 'groovy2.txt', groovy3.txt'] == files

Writing to Files

Appending Content

You can also get a File object (passing the path to the File constructor) and append text to it with a << operator:

// Using the leftShift operator:
new File('/Users/paford/Documents/test.txt') << 'See how easy it is to add text to a file.\n'

Overwriting Files

However, that method appends, what if you want to overwrite the file content completely? Groovy provides a File.write() method that does that:

// Writing to the files with the write method:
def file1 = new File('groovy1.txt')
file1.write 'Working with files the Groovy way is easy.\n'

References