Read / Write files with Apache Groovy
Reading files
In the previous post I talked about some substantial differences between Groovy and Java, now we are going to talk about how to work with Files in Groovy
First, reading files in Groovy is just as easy or easier than reading files in Java. Of course not, let’s first look at an example of reading files in Java which would look something like this.
Since Java 8
Path filePath = Path.of("file.txt");
StringBuilder contentBuilder = new StringBuilder();
try (Stream<String> stream = Files.lines(Paths.get(filePath), StandardCharsets.UTF_8)) {
//Read the content with Stream
stream.forEach(s -> contentBuilder.append(s).append("\n"));
} catch (IOException e) {
e.printStackTrace();
}
String fileContent = contentBuilder.toString();
Of course there are ways to do it in less code, personally I do prefer Groovy’s style
String fileContent = new File("file.txt").text
or we can read line by line
new File("file.txt").eachLine { line -> println line }
Writing into a file
Groovy is very intuitive, there is not much to explain, now, if we want to write into file,
we just need to create a PrintWriter object for the file and then call the method print or println
to write on it as in the following sample.
File file = new File('output.txt')
out = file.newPrintWriter()
10.times { out.println("line $it") }
out.close() // The file needs to be closed for it to be saved to the file
As we saw, reading/writing files in Groovy is quite simple.
Now I will show you some samples that might help you when you work with files on Groovy
Collect filenames on a directory
List<String> fileNames = new File("<your-directory>")
.listFiles() // method from Java 8
.collect{ it.name } // closure from Groovy
Filter files on a directory with a REGEX
String regex = /.*\.pdf/
List<String> fileNames = []
new File("<your-directory>")
.eachFileMatch(~regex) { file -> // Closure eachFileMatch
fileNames << file.name // The file variable is of type java.io.File
}
Iterate over directories
import groovy.io.FileType
new File("<your-directory>")
.eachFile(FileType.DIRECTORIES) { directory -> // Closure eachFile
fileNames << directory.name // The directory variable is of type java.io.File
}
There more cool things that you can easily do with Groovy and Files, iterate over a directory, find all the files in a subdirectory, find text on a file, etc.
The last example shows how to collect all occurrences of a specific word, it will print the file name,
the word and the lines on the file where it was found.
File dir = new File('<your-directory>')
String regex = /.*\.txt/
String word = "word"
dir.eachFileMatch(~regex) { file ->
List lineNumbers = []
file.readLines()
.eachWithIndex{ line, index ->
if(line.contains(word)) {
lineNumbers << index
}
}
if(lineNumbers) {
println "File: ${file.name} contains [$word] at lines $lineNumbers"
}
}
Thanks for reading I hope this samples can help you to better understand how Groovy works with Files.