JSONData.java
package org.djutils.data.json;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Reader;
import java.io.Writer;
import java.util.ArrayList;
import java.util.IllegalFormatException;
import java.util.List;
import org.djutils.data.DataColumn;
import org.djutils.data.DataRecord;
import org.djutils.data.DataTable;
import org.djutils.data.ListDataTable;
import org.djutils.data.SimpleDataColumn;
import org.djutils.data.serialization.TextSerializationException;
import org.djutils.data.serialization.TextSerializer;
import org.djutils.exceptions.Throw;
import org.djutils.primitives.Primitive;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;
import com.google.gson.stream.JsonWriter;
/**
* JSONData takes care of reading and writing of table data in JSON format. The reader and writer use a streaming API to avoid
* excessive memory use. The class can be used, e.g., as follows:
*
* <pre>
* DataTable dataTable = new ListDataTable("data", "dataTable", columns);
* Writer writer = new FileWriter("c:/data/data.json");
* JSONData.writeData(writer, dataTable);
* </pre>
*
* The JSON document has the following structure:
*
* <pre>
* {
* "table": {
* "id": "tableId",
* "description": "table description",
* "class": "org.djutils.data.ListDataTable"",
* "columns": [
* {
* "nr": "0",
* "id": "time",
* "description": "time in [s]",
* "class": "org.djtils.vdouble.scalar.Time",
* },
* {
* "nr": "1",
* "id": "value",
* "description": "value [cm]",
* "class": "double",
* },
* {
* "nr": "2",
* "id": "comment",
* "description": "comment",
* "class": "java.lang.String",
* },
* ]
* },
* "data": [
* [ { "0" : "2" }, { "1": "14.6" }, { "2" : "normal" } ],
* [ { "0" : "4" }, { "1": "18.7" }, { "2" : "normal" } ],
* [ { "0" : "6" }, { "1": "21.3" }, { "2" : "abnormal" } ]
* ]
* }
* </pre>
*
* Copyright (c) 2020-2020 Delft University of Technology, Jaffalaan 5, 2628 BX Delft, the Netherlands. All rights reserved. See
* for project information <a href="https://djutils.org" target="_blank"> https://djutils.org</a>. The DJUTILS project is
* distributed under a three-clause BSD-style license, which can be found at
* <a href="https://djutils.org/docs/license.html" target="_blank"> https://djutils.org/docs/license.html</a>. <br>
* @author <a href="https://www.tudelft.nl/averbraeck">Alexander Verbraeck</a>
* @author <a href="https://www.tudelft.nl/pknoppers">Peter Knoppers</a>
* @author <a href="http://www.transport.citg.tudelft.nl">Wouter Schakel</a>
*/
public final class JSONData
{
/**
* Utility class, no public constructor.
*/
private JSONData()
{
// utility class
}
/**
* Write the data from the data table in JSON format. The writer is closed after finishing the writing of the data.
* @param writer Writer; the writer that writes the data, e.g. to a file
* @param dataTable the data table to write
* @throws IOException on I/O error when writing the data
* @throws TextSerializationException on unknown data type for serialization
*/
public static void writeData(final Writer writer, final DataTable dataTable) throws IOException, TextSerializationException
{
JsonWriter jw = new JsonWriter(writer);
jw.setIndent(" ");
// write the table metadata
jw.beginObject();
jw.name("table").beginObject();
jw.name("id").value(dataTable.getId());
jw.name("description").value(dataTable.getDescription());
jw.name("class").value(dataTable.getClass().getName());
jw.name("columns").beginArray();
int index = 0;
for (DataColumn<?> column : dataTable.getColumns())
{
jw.beginObject();
jw.name("nr").value(index++);
jw.name("id").value(column.getId());
jw.name("description").value(column.getDescription());
jw.name("type").value(column.getValueType().getName());
jw.endObject();
}
jw.endArray(); // columns
jw.endObject(); // table
// initialize the serializers
TextSerializer<?>[] serializers = new TextSerializer[dataTable.getNumberOfColumns()];
for (int i = 0; i < dataTable.getNumberOfColumns(); i++)
{
DataColumn<?> column = dataTable.getColumns().get(i);
serializers[i] = TextSerializer.resolve(column.getValueType());
}
// write the data
jw.name("data").beginArray();
// write the records
for (DataRecord record : dataTable)
{
Object[] values = record.getValues();
jw.beginArray();
jw.setIndent("");
for (int i = 0; i < dataTable.getNumberOfColumns(); i++)
{
jw.beginObject().name(String.valueOf(i)).value(serializers[i].serialize(values[i])).endObject();
}
jw.endArray(); // record
jw.setIndent(" ");
}
// end JSON document
jw.endArray(); // data array
jw.endObject(); // data
jw.close();
writer.close();
}
/**
* Write the data from the data table in JSON format.
* @param filename String; the file name to write the data to
* @param dataTable the data table to write
* @throws IOException on I/O error when writing the data
* @throws TextSerializationException on unknown data type for serialization
*/
public static void writeData(final String filename, final DataTable dataTable)
throws IOException, TextSerializationException
{
writeData(new FileWriter(filename), dataTable);
}
/**
* Read the data from the csv-file into the data table. Use the metadata to reconstruct the data table.
* @param reader Reader; the reader that can read the data, e.g. from a file
* @return dataTable the data table reconstructed from the meta data and filled with the data
* @throws IOException on I/O error when reading the data
* @throws TextSerializationException on unknown data type for serialization
*/
public static DataTable readData(final Reader reader) throws IOException, TextSerializationException
{
// read the metadata and reconstruct the data table
JsonReader jr = new JsonReader(reader);
jr.beginObject();
readName(jr, "table");
jr.beginObject();
String[] tableProperties = new String[3];
tableProperties[0] = readValue(jr, "id");
tableProperties[1] = readValue(jr, "description");
tableProperties[2] = readValue(jr, "class");
Throw.when(!tableProperties[2].endsWith("ListDataTable"), IOException.class,
"Currently, this method can only recreate a ListDataTable");
// column metadata
List<DataColumn<?>> columns = new ArrayList<>();
int index = 0;
readName(jr, "columns");
jr.beginArray();
while (jr.peek().equals(JsonToken.BEGIN_OBJECT))
{
String[] columnProperties = new String[4];
jr.beginObject();
columnProperties[0] = readValue(jr, "nr");
columnProperties[1] = readValue(jr, "id");
columnProperties[2] = readValue(jr, "description");
columnProperties[3] = readValue(jr, "type");
jr.endObject();
if (Integer.valueOf(columnProperties[0]).intValue() != index)
{
throw new IOException("column nr not ok");
}
String type = columnProperties[3];
Class<?> valueClass = Primitive.forName(type);
if (valueClass == null)
{
try
{
valueClass = Class.forName(type);
}
catch (ClassNotFoundException exception)
{
jr.close();
reader.close();
throw new IOException("Could not find class " + type, exception);
}
}
@SuppressWarnings({"rawtypes", "unchecked"})
DataColumn<?> column = new SimpleDataColumn(columnProperties[1], columnProperties[2], valueClass);
columns.add(column);
index++;
}
jr.endArray(); // columns
jr.endObject(); // table
ListDataTable dataTable = new ListDataTable(tableProperties[0], tableProperties[1], columns);
// obtain the serializers
TextSerializer<?>[] serializers = new TextSerializer[dataTable.getNumberOfColumns()];
for (int i = 0; i < dataTable.getNumberOfColumns(); i++)
{
DataColumn<?> column = dataTable.getColumns().get(i);
serializers[i] = TextSerializer.resolve(column.getValueType());
}
// read the data file records
readName(jr, "data");
jr.beginArray();
while (jr.peek().equals(JsonToken.BEGIN_ARRAY))
{
Object[] values = new Object[columns.size()];
jr.beginArray();
for (int i = 0; i < dataTable.getNumberOfColumns(); i++)
{
jr.beginObject();
values[i] = serializers[i].deserialize(readValue(jr, "" + i));
jr.endObject();
}
jr.endArray(); // record
dataTable.addRecord(values);
}
// end JSON document
jr.endArray(); // data array
jr.endObject(); // data
jr.close();
reader.close();
return dataTable;
}
/**
* Read a name - value pair from the JSON file where name has to match the given tag name.
* @param jr the JSON stream reader
* @param tag the tag to retrieve
* @return the value belonging to the tag
* @throws IllegalFormatException when the next element in the file did not contain the right tag
* @throws IOException when reading from the stream raises an exception
*/
private static String readValue(final JsonReader jr, final String tag) throws IllegalFormatException, IOException
{
Throw.when(!jr.nextName().equals(tag), IllegalFormatException.class, "readValue: no %s object", tag);
return jr.nextString();
}
/**
* Read a name -from the JSON file where name has to match the given tag name.
* @param jr the JSON stream reader
* @param tag the tag to retrieve
* @throws IllegalFormatException when the next element in the file did not contain the right tag
* @throws IOException when reading from the stream raises an exception
*/
private static void readName(final JsonReader jr, final String tag) throws IllegalFormatException, IOException
{
Throw.when(!jr.nextName().equals(tag), IllegalFormatException.class, "readName: no %s object", tag);
}
/**
* Read the data from the csv-file into the data table. Use the metadata to reconstruct the data table.
* @param filename String; the file name to read the data from
* @return dataTable the data table reconstructed from the meta data and filled with the data
* @throws IOException on I/O error when reading the data
* @throws TextSerializationException on unknown data type for serialization
*/
public static DataTable readData(final String filename) throws IOException, TextSerializationException
{
return readData(new FileReader(filename));
}
}