Reading CSV Files

1. Adding Apache commons csv library as dependencies
2. Putting your csv file in the project
3. Read the CSV file in your code

Put the following in your build.gradle dependencies{} section. The current version of commons cvs is 1.6. You might want to use a newer version upon its release.

compile group: 'org.apache.commons', name: 'commons-csv', version: '1.6'

For Grails 3 project, one of the good place to store your file is the /grails-app/conf directory. You can even create your own directory within it. We are going to use MTR Lines (except Airport Express & Light Rail) Fares mtr_lines_fares.csv as an example, and it can be downloaded at here.

The data look like the follow. Play attention to the header.

We can read the csv in a Grails controller or service. We are going to do this in a controller.

class PriceController {
    def grailsResourceLocator

    def index() {
        String strings = grailsResourceLocator.findResourceForURI('classpath:/mtr_lines_fares.csv').inputStream.getText(StandardCharsets.UTF_8.name())
        Iterable<CSVRecord> records = CSVFormat.RFC4180.withFirstRecordAsHeader().parse(new StringReader(strings))
        StringBuilder sb = new StringBuilder()
        for (CSVRecord cvsRecord : records) {
            try {
                sb.append(cvsRecord.get("SRC_STATION_NAME")).append(", ")
                sb.append(cvsRecord.get("SRC_STATION_ID")).append(", ")
                sb.append(cvsRecord.get("DEST_STATION_NAME")).append(", ")
                sb.append(cvsRecord.get("DEST_STATION_ID")).append(", ")
                sb.append(cvsRecord.get("OCT_ADT_FARE")).append(", ")
                sb.append(cvsRecord.get("OCT_STD_FARE")).append(", ")
                sb.append(cvsRecord.get("SINGLE_ADT_FARE")).append(", ")
                sb.append(cvsRecord.get("OCT_CON_CHILD_FARE")).append(", ")
                sb.append(cvsRecord.get("OCT_CON_ELDERLY_FARE")).append(", ")
                sb.append(cvsRecord.get("OCT_CON_PWD_FARE")).append(", ")
                sb.append(cvsRecord.get("SINGLE_CON_CHILD_FARE")).append(", ")
                sb.append(cvsRecord.get("SINGLE_CON_ELDERLY_FARE"))
                sb.append("<br>")
            } catch (Exception ignored) {
                log.error("Unable to convert ${cvsRecord.toString()}")
            }
        }
        render(sb.toString())
    }
}

First we load our csv file with grailsResourceLocator.

String strings = grailsResourceLocator.findResourceForURI('classpath:/mtr_lines_fares.csv').inputStream.getText(StandardCharsets.UTF_8.name())

Than parse it with withFirstRecordAsHeader. It will return an iterable CSVRecord, which is basically a map with headers as keys.

Iterable<CSVRecord> records = CSVFormat.RFC4180.withFirstRecordAsHeader().parse(new StringReader(strings))

With the iterable records, we can use a loop to loop though them to extract the data we want. Here we use the csv header as the key to obtains data in each column.

for (CSVRecord cvsRecord : records) {
   try {
      sb.append(cvsRecord.get("SRC_STATION_NAME")).append(", ")
      .
      .
      .
   } catch (Exception ignored) {
      log.error("Unable to convert ${cvsRecord.toString()}")
}

You can parse the string with

Iterable<CSVRecord> records = CSVFormat.RFC4180.parse(new StringReader(strings))

And loop though the records with

for (CSVRecord cvsRecord : records) {
   try {
      sb.append(cvsRecord.get(0).append(", ")
      sb.append(cvsRecord.get(1).append(", ")
      sb.append(cvsRecord.get(2).append(", ")
      .
      .
      .
   } catch (Exception ignored) {
      log.error("Unable to convert ${cvsRecord.toString()}")
}