Insane Programming Java ramblings and finds on the net

Having fun with JSON and DbUnit

DbUnit is one of those invaluable frameworks in my toolbox. The only thing I don't like are the XML dataset formats. Having played around with JSON for the last couple of weeks, I decided a nice exercise would be to create a JSON-based dataset.

I started off with the dataset format I'd like to use

{
  "mytable":
  [
    {
      "field1": "value1",
      "field2": "value2"
    },
    {
      "field1": "value3",
    }
  ]
}

This would create 2 rows in the mytable database table, with the second row having its field2 set to NULL. Writing the code for DbUnit to be able to process this took me about 15 minutes (including unit tests for it). It uses Jackson for the JSON processing. Here it is:

import org.codehaus.jackson.map.ObjectMapper;
import org.dbunit.dataset.*;
import org.dbunit.dataset.datatype.DataType;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.*;

/**
 * DBUnit DataSet format for JSON based datasets. It is similar to the flat XML layout,
 * but has some improvements (columns are calculated by parsing the entire dataset, not just
 * the first row). It uses Jackson, a fast JSON processor.
 * <br/><br/>
 * The format looks like this:
 * <br/>
 * <pre>
 * {
 *    "&lt;table_name&gt;": [
 *        {
 *             "&lt;column&gt;":&lt;value&gt;,
 *             ...
 *        },
 *        ...
 *    ],
 *    ...
 * }
 * </pre>
 * <br/>
 * I.e.:
 * <br/>
 * <pre>
 * {
 *    "test_table": [
 *        {
 *             "id":1,
 *             "code":"JSON dataset",
 *        },
 *        {
 *             "id":2,
 *             "code":"Another row",
 *        }
 *    ],
 *    "another_table": [
 *        {
 *             "id":1,
 *             "description":"Foo",
 *        },
 *        {
 *             "id":2,
 *             "description":"Bar",
 *        }
 *    ],
 *    ...
 * }
 * </pre>
 *
 * @author Lieven DOCLO
 */
public class JSONDataSet extends AbstractDataSet {
    // The parser for the dataset JSON file
    private JSONITableParser tableParser = new JSONITableParser();

    // The tables after parsing
    private List<ITable> tables;

    /**
     * Creates a JSON dataset based on a file
     * @param file A JSON dataset file
     */
    public JSONDataSet(File file) {
        tables = tableParser.getTables(file);
    }

    /**
     * Creates a JSON dataset based on an inputstream
     * @param is An inputstream pointing to a JSON dataset
     */
    public JSONDataSet(InputStream is) {
        tables = tableParser.getTables(is);
    }

    @Override
    protected ITableIterator createIterator(boolean reverse) throws DataSetException {
        return new DefaultTableIterator(tables.toArray(new ITable[tables.size()]));
    }

    private class JSONITableParser {

        private ObjectMapper mapper = new ObjectMapper();

        /**
         * Parses a JSON dataset file and returns the list of DBUnit tables contained in
         * that file
         * @param jsonFile A JSON dataset file
         * @return A list of DBUnit tables
         */
        public List<ITable> getTables(File jsonFile) {
            try {
                return getTables(new FileInputStream(jsonFile));
            } catch (IOException e) {
                throw new RuntimeException(e.getMessage(), e);
            }
        }

        /**
         * Parses a JSON dataset input stream and returns the list of DBUnit tables contained in
         * that input stream
         * @param jsonStream A JSON dataset input stream
         * @return A list of DBUnit tables
         */
        @SuppressWarnings("unchecked")
        public List<ITable> getTables(InputStream jsonStream) {
            List<ITable> tables = new ArrayList<ITable>();
            try {
                // get the base object tree from the JSON stream
                Map<String, Object> dataset = mapper.readValue(jsonStream, Map.class);
                // iterate over the tables in the object tree
                for (Map.Entry<String, Object> entry : dataset.entrySet()) {
                    // get the rows for the table
                    List<Map<String, Object>> rows = (List<Map<String, Object>>) entry.getValue();
                    ITableMetaData meta = getMetaData(entry.getKey(), rows);
                    // create a table based on the metadata
                    DefaultTable table = new DefaultTable(meta);
                    int rowIndex = 0;
                    // iterate through the rows and fill the table
                    for (Map<String, Object> row : rows) {
                        fillRow(table, row, rowIndex++);
                    }
                    // add the table to the list of DBUnit tables
                    tables.add(table);
                }

            } catch (IOException e) {
                throw new RuntimeException(e.getMessage(), e);
            }
            return tables;
        }

        /**
         * Gets the table meta data based on the rows for a table
         * @param tableName The name of the table
         * @param rows The rows of the table
         * @return The table metadata for the table
         */
        private ITableMetaData getMetaData(String tableName, List<Map<String, Object>> rows) {
            Set<String> columns = new LinkedHashSet<String>();
            // iterate through the dataset and add the column names to a set
            for (Map<String, Object> row : rows) {
                for (Map.Entry<String, Object> column : row.entrySet()) {
                    columns.add(column.getKey());
                }
            }
            List<Column> list = new ArrayList<Column>(columns.size());
            // create a list of DBUnit columns based on the column name set
            for (String s : columns) {
                list.add(new Column(s, DataType.UNKNOWN));
            }
            return new DefaultTableMetaData(tableName, list.toArray(new Column[list.size()]));
        }

        /**
         * Fill a table row
         * @param table The table to be filled
         * @param row A map containing the column values
         * @param rowIndex The index of the row to te filled
         */
        private void fillRow(DefaultTable table, Map<String, Object> row, int rowIndex) {
            try {
                table.addRow();
                // set the column values for the current row
                for (Map.Entry<String, Object> column : row.entrySet()) {
                    table.setValue(rowIndex, column.getKey(), column.getValue());

                }
            } catch (Exception e) {
                throw new RuntimeException(e.getMessage(), e);
            }
        }
    }
}

I tested it with 1000+ row dataset and it is quite fast. It's even documented! Have fun.