Groovy: reading and writing files - appending content

In order to handle files Groovy has a class called File. Let's see some of the basic operations you can do with files.

filename = 'examples/data/count_digits.txt'

// read all the content of the file into a single string
File fh1 = new File(filename)
text = fh1.getText('UTF-8')

// read all the lines into a list, each line is an element in the list
File fh2 = new File(filename)
def lines = fh2.readLines()
for (line in lines) {
    // ...
}


File fh3 = new File(filename)
LineNumberReader reader = fh3.newReader()
while ((line = reader.readLine()) != null) {
    // ...
}

Write a new file

This will remove the content of the old file and start a new file.

File file = new File("out.txt")
file.write "First line\n"
file << "Second line\n"

println file.text

This will append to the end of the file.

File file = new File("out.txt")
file.append("hello\n")
println file.text

Write and Append

If we mix the calls to write and to append we'll get some strange results. For example the following code will only store "third" in the file.

File file = new File("out.txt")
file.write("first\n")
file.append("second\n")
file.write("third\n")

println file.text

Don't do this!

timestamp: 2018-06-03T14:30:01 tags:

• File
• getText
• readLines
• newReader
• readLine
• write
• append