1 package org.djutils.data.json;
2
3 import java.io.FileReader;
4 import java.io.FileWriter;
5 import java.io.IOException;
6 import java.io.Reader;
7 import java.io.Writer;
8 import java.util.ArrayList;
9 import java.util.IllegalFormatException;
10 import java.util.List;
11
12 import org.djutils.data.DataColumn;
13 import org.djutils.data.DataRecord;
14 import org.djutils.data.DataTable;
15 import org.djutils.data.ListDataTable;
16 import org.djutils.data.SimpleDataColumn;
17 import org.djutils.data.serialization.TextSerializationException;
18 import org.djutils.data.serialization.TextSerializer;
19 import org.djutils.exceptions.Throw;
20 import org.djutils.primitives.Primitive;
21
22 import com.google.gson.stream.JsonReader;
23 import com.google.gson.stream.JsonToken;
24 import com.google.gson.stream.JsonWriter;
25
26 /**
27 * JSONData takes care of reading and writing of table data in JSON format. The reader and writer use a streaming API to avoid
28 * excessive memory use. The class can be used, e.g., as follows:
29 *
30 * <pre>
31 * DataTable dataTable = new ListDataTable("data", "dataTable", columns);
32 * Writer writer = new FileWriter("c:/data/data.json");
33 * JSONData.writeData(writer, dataTable);
34 * </pre>
35 *
36 * The JSON document has the following structure:
37 *
38 * <pre>
39 * {
40 * "table": {
41 * "id": "tableId",
42 * "description": "table description",
43 * "class": "org.djutils.data.ListDataTable"",
44 * "columns": [
45 * {
46 * "nr": "0",
47 * "id": "time",
48 * "description": "time in [s]",
49 * "class": "org.djtils.vdouble.scalar.Time",
50 * },
51 * {
52 * "nr": "1",
53 * "id": "value",
54 * "description": "value [cm]",
55 * "class": "double",
56 * },
57 * {
58 * "nr": "2",
59 * "id": "comment",
60 * "description": "comment",
61 * "class": "java.lang.String",
62 * },
63 * ]
64 * },
65 * "data": [
66 * [ { "0" : "2" }, { "1": "14.6" }, { "2" : "normal" } ],
67 * [ { "0" : "4" }, { "1": "18.7" }, { "2" : "normal" } ],
68 * [ { "0" : "6" }, { "1": "21.3" }, { "2" : "abnormal" } ]
69 * ]
70 * }
71 * </pre>
72 *
73 * Copyright (c) 2020-2020 Delft University of Technology, Jaffalaan 5, 2628 BX Delft, the Netherlands. All rights reserved. See
74 * for project information <a href="https://djutils.org" target="_blank"> https://djutils.org</a>. The DJUTILS project is
75 * distributed under a three-clause BSD-style license, which can be found at
76 * <a href="https://djutils.org/docs/license.html" target="_blank"> https://djutils.org/docs/license.html</a>. <br>
77 * @author <a href="https://www.tudelft.nl/averbraeck">Alexander Verbraeck</a>
78 * @author <a href="https://www.tudelft.nl/pknoppers">Peter Knoppers</a>
79 * @author <a href="http://www.transport.citg.tudelft.nl">Wouter Schakel</a>
80 */
81 public final class JSONData
82 {
83 /**
84 * Utility class, no public constructor.
85 */
86 private JSONData()
87 {
88 // utility class
89 }
90
91 /**
92 * Write the data from the data table in JSON format.
93 * @param writer Writer; the writer that writes the data, e.g. to a file
94 * @param dataTable the data table to write
95 * @throws IOException on I/O error when writing the data
96 * @throws TextSerializationException on unknown data type for serialization
97 */
98 public static void writeData(final Writer writer, final DataTable dataTable) throws IOException, TextSerializationException
99 {
100 JsonWriter jw = null;
101 try
102 {
103 jw = new JsonWriter(writer);
104 jw.setIndent(" ");
105
106 // write the table metadata
107 jw.beginObject();
108 jw.name("table").beginObject();
109 jw.name("id").value(dataTable.getId());
110 jw.name("description").value(dataTable.getDescription());
111 jw.name("class").value(dataTable.getClass().getName());
112 jw.name("columns").beginArray();
113 int index = 0;
114 for (DataColumn<?> column : dataTable.getColumns())
115 {
116 jw.beginObject();
117 jw.name("nr").value(index++);
118 jw.name("id").value(column.getId());
119 jw.name("description").value(column.getDescription());
120 jw.name("type").value(column.getValueType().getName());
121 jw.endObject();
122 }
123 jw.endArray(); // columns
124 jw.endObject(); // table
125
126 // initialize the serializers
127 TextSerializer<?>[] serializers = new TextSerializer[dataTable.getNumberOfColumns()];
128 for (int i = 0; i < dataTable.getNumberOfColumns(); i++)
129 {
130 DataColumn<?> column = dataTable.getColumns().get(i);
131 serializers[i] = TextSerializer.resolve(column.getValueType());
132 }
133
134 // write the data
135 jw.name("data").beginArray();
136
137 // write the records
138 for (DataRecord record : dataTable)
139 {
140 Object[] values = record.getValues();
141 jw.beginArray();
142 jw.setIndent("");
143 for (int i = 0; i < dataTable.getNumberOfColumns(); i++)
144 {
145 jw.beginObject().name(String.valueOf(i)).value(serializers[i].serialize(values[i])).endObject();
146 }
147 jw.endArray(); // record
148 jw.setIndent(" ");
149 }
150
151 // end JSON document
152 jw.endArray(); // data array
153 jw.endObject(); // data
154 }
155 finally
156 {
157 if (null != jw)
158 {
159 jw.close();
160 }
161 }
162 }
163
164 /**
165 * Write the data from the data table in JSON format.
166 * @param filename String; the file name to write the data to
167 * @param dataTable the data table to write
168 * @throws IOException on I/O error when writing the data
169 * @throws TextSerializationException on unknown data type for serialization
170 */
171 public static void writeData(final String filename, final DataTable dataTable)
172 throws IOException, TextSerializationException
173 {
174 FileWriter fw = null;
175 try
176 {
177 fw = new FileWriter(filename);
178 writeData(fw, dataTable);
179 }
180 finally
181 {
182 if (null != fw)
183 {
184 fw.close();
185 }
186 }
187 }
188
189 /**
190 * Read the data from the csv-file into the data table. Use the metadata to reconstruct the data table.
191 * @param reader Reader; the reader that can read the data, e.g. from a file
192 * @return dataTable the data table reconstructed from the meta data and filled with the data
193 * @throws IOException on I/O error when reading the data
194 * @throws TextSerializationException on unknown data type for serialization
195 */
196 public static DataTable readData(final Reader reader) throws IOException, TextSerializationException
197 {
198 JsonReader jr = null;
199 try
200 {
201 // read the metadata and reconstruct the data table
202 jr = new JsonReader(reader);
203 jr.beginObject();
204 readName(jr, "table");
205 jr.beginObject();
206 String[] tableProperties = new String[3];
207 tableProperties[0] = readValue(jr, "id");
208 tableProperties[1] = readValue(jr, "description");
209 tableProperties[2] = readValue(jr, "class");
210 Throw.when(!tableProperties[2].endsWith("ListDataTable"), IOException.class,
211 "Currently, this method can only recreate a ListDataTable");
212
213 // column metadata
214 List<DataColumn<?>> columns = new ArrayList<>();
215 int index = 0;
216 readName(jr, "columns");
217 jr.beginArray();
218 while (jr.peek().equals(JsonToken.BEGIN_OBJECT))
219 {
220 String[] columnProperties = new String[4];
221 jr.beginObject();
222 columnProperties[0] = readValue(jr, "nr");
223 columnProperties[1] = readValue(jr, "id");
224 columnProperties[2] = readValue(jr, "description");
225 columnProperties[3] = readValue(jr, "type");
226 jr.endObject();
227
228 if (Integer.valueOf(columnProperties[0]).intValue() != index)
229 {
230 throw new IOException("column nr not ok");
231 }
232 String type = columnProperties[3];
233 Class<?> valueClass = Primitive.forName(type);
234 if (valueClass == null)
235 {
236 try
237 {
238 valueClass = Class.forName(type);
239 }
240 catch (ClassNotFoundException exception)
241 {
242 throw new IOException("Could not find class " + type, exception);
243 }
244 }
245 @SuppressWarnings({ "rawtypes", "unchecked" })
246 DataColumn<?> column = new SimpleDataColumn(columnProperties[1], columnProperties[2], valueClass);
247 columns.add(column);
248 index++;
249 }
250 jr.endArray(); // columns
251 jr.endObject(); // table
252
253 ListDataTablestDataTable">ListDataTable dataTable = new ListDataTable(tableProperties[0], tableProperties[1], columns);
254
255 // obtain the serializers
256 TextSerializer<?>[] serializers = new TextSerializer[dataTable.getNumberOfColumns()];
257 for (int i = 0; i < dataTable.getNumberOfColumns(); i++)
258 {
259 DataColumn<?> column = dataTable.getColumns().get(i);
260 serializers[i] = TextSerializer.resolve(column.getValueType());
261 }
262
263 // read the data file records
264 readName(jr, "data");
265 jr.beginArray();
266 while (jr.peek().equals(JsonToken.BEGIN_ARRAY))
267 {
268 Object[] values = new Object[columns.size()];
269 jr.beginArray();
270 for (int i = 0; i < dataTable.getNumberOfColumns(); i++)
271 {
272 jr.beginObject();
273 values[i] = serializers[i].deserialize(readValue(jr, "" + i));
274 jr.endObject();
275 }
276 jr.endArray(); // record
277 dataTable.addRecord(values);
278 }
279
280 // end JSON document
281 jr.endArray(); // data array
282 jr.endObject(); // data
283 return dataTable;
284 }
285 finally
286 {
287 if (null != jr)
288 {
289 jr.close();
290 }
291 }
292 }
293
294 /**
295 * Read a name - value pair from the JSON file where name has to match the given tag name.
296 * @param jr the JSON stream reader
297 * @param tag the tag to retrieve
298 * @return the value belonging to the tag
299 * @throws IllegalFormatException when the next element in the file did not contain the right tag
300 * @throws IOException when reading from the stream raises an exception
301 */
302 private static String readValue(final JsonReader jr, final String tag) throws IllegalFormatException, IOException
303 {
304 Throw.when(!jr.nextName().equals(tag), IllegalFormatException.class, "readValue: no %s object", tag);
305 return jr.nextString();
306 }
307
308 /**
309 * Read a name -from the JSON file where name has to match the given tag name.
310 * @param jr the JSON stream reader
311 * @param tag the tag to retrieve
312 * @throws IllegalFormatException when the next element in the file did not contain the right tag
313 * @throws IOException when reading from the stream raises an exception
314 */
315 private static void readName(final JsonReader jr, final String tag) throws IllegalFormatException, IOException
316 {
317 Throw.when(!jr.nextName().equals(tag), IllegalFormatException.class, "readName: no %s object", tag);
318 }
319
320 /**
321 * Read the data from the csv-file into the data table. Use the metadata to reconstruct the data table.
322 * @param filename String; the file name to read the data from
323 * @return dataTable the data table reconstructed from the meta data and filled with the data
324 * @throws IOException on I/O error when reading the data
325 * @throws TextSerializationException on unknown data type for serialization
326 */
327 public static DataTable readData(final String filename) throws IOException, TextSerializationException
328 {
329 FileReader fr = null;
330 try
331 {
332 fr = new FileReader(filename);
333 return readData(fr);
334 }
335 finally
336 {
337 if (null != fr)
338 {
339 fr.close();
340 }
341 }
342 }
343
344 }