Griddle is a Groovy library for easily processing tabular data. Currently, it supports Excel files (both HSSF and XSSF) and CSV files.

First, add a dependency to your build file. Releases are published to Bintray JCenter. See the change log for the latest version.

Gradle:

repositories {
    jcenter()
}
dependencies {
    compile "com.commercehub:griddle:3.0.0"
}

Maven:

<dependency>
    <groupId>com.commercehub</groupId>
    <artifactId>griddle</artifactId>
    <version>3.0.0</version>
</dependency>

Next, create the desired instance of TabularDataSource.

Please note that com.commercehub.griddle.opencsv.CSVTabularDataSource is deprecated; use com.commercehub.griddle.supercsv.CSVTabularDataSource instead.

def tabularDataSource = new CSVTabularDataSource()
// OR
def tabularDataSource = new HSSFTabularDataSource()
// OR
def tabularDataSource = new XSSFTabularDataSource()
// OR
def tabularDataSource = new StreamingXSSFTabularDataSource()

Then use the TabularDataSource to process files. The withFile method is used to provide access to TabularData objects processed from a file. Each TabularData object provides access to the names of the columns in that table, as well as the rows in the table (represented as a Map of String, column name to cell value). The file is automatically closed at the end of the closure passed to withFile.

def file = new File("myfile.xlsx")
tabularDataSource.withFile(file) { Iterable<TabularData> tables ->
    for (table in tables) {
        println "Processing a table with columns ${table.columnNames}..."
        for (row in table.rows) {
            println "Row: ${row}"
        }
        println "Completed table processing."
    }
}

Sometimes, the column names or values that you want when processing aren't exactly what is present in your file. For example, you may want to trim whitespace from data cell values, or treat column names in a case-insensitive manner. To accomplish this, set a transformer using the setColumnNameTransformer or setValueTransformer methods on TabularDataSource. For common cases, you can use pre-written transformers provided by the Transformers class.

Excel cells are actually rather complex. They have different types, can contain formulas, have styles, have a presentation format, etc. To control how Apache POI Cells are converted into Strings, implement the ExcelCellMapper interface and provide an instance to the HSSFTabularDataSource/XSSFTabularDataSource constructor. Note, the StreamingXSSFTabularDataSource does not yet support cell mapping using this mechanism.

Sometimes, it may be useful to ignore certain rows in the file. To do this, when calling the getRows method on TabularDataSource, pass a closure defining your row skip criteria. This closure is passed the row Map as the argument, and should return true if the row should be skipped.

The StreamingXSSFTabularDataSource relies on org.apache.poi.xssf.eventusermodel.XSSFSheetXMLHandler to format output, which provides for minimal formatting extension points. Overriding the handlerBuilder method of StreamingXSSFTabularData to return a customized org.apache.poi.xssf.eventusermodel.XSSFSheetXMLHandler is the only current mechanism to manipulate the default formatting/mapping behavior.

Releases are uploaded to Bintray via the gradle-release plugin and gradle-bintray-plugin. To upload a new release, you need to be a member of the commercehub-oss Bintray organization. You need to specify your Bintray username and API key when uploading. Your API key can be found on your Bintray user profile page. You can put your username and API key in ~/.gradle/gradle.properties like so:

bintrayUserName = johndoe
bintrayApiKey = 0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef

Then, to upload the release:

./gradlew release

Alternatively, you can specify your Bintray username and API key on the command line:

./gradlew -PbintrayUserName=johndoe -PbintrayApiKey=0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef release

The release task will prompt you to enter the version to be released, and will create and push a release tag for the specified version. It will also upload the release artifacts to Bintray.

After the release artifacts have been uploaded to Bintray, they must be published to become visible to users. See Bintray's Publishing documentation for instructions.

After publishing the release on Bintray, it's also nice to create a GitHub release. To do so:

• Visit the project's releases page
• Click the "Draft a new release" button
• Select the tag that was created by the Gradle release task
• Enter a title; typically, this should match the tag (e.g. "1.2.0")
• Enter a description of what changed since the previous release (see the changelog)
• Click the "Publish release" button