How can you generate a JSON sample with dummy data from a Java class definition? (Note: I am not asking about generating JSON from a POJO. This is something that has been asked before on stackoverflow).
What I want is to generate some sample dummy data from a Java class directly. For example you have a class like this one:
public class Reservation {
@ApiModelProperty(value = "")
private Traveller leadTraveller = null;
@ApiModelProperty(example = "2", value = "")
private Integer sourceSystemID = null;
@ApiModelProperty(value = "")
private String recordLocation = null;
@ApiModelProperty(example = "2010", value = "")
private Integer recordLocatorYear = null;
}
And then you have a function which generates without creating a POJO a JSON string with dummy values like:
{
"leadTraveller": {
"firstNames": "firstNames",
"lastName": "lastName",
"email": "email",
"travellerGUID": "travellerGUID",
"travellerRefs": [{
"customerReportingRank": 37,
"value": "value",
"description": "description"
}]
},
"sourceSystemID": 38,
"recordLocation": "recordLocation",
"recordLocatorYear": 9
}
Is there a library which can do this by default?
I have tried to solve this problem using Java code with these Maven dependencies:
<dependency>
<groupId>fctg-ngrp</groupId>
<artifactId>model-core</artifactId>
<version>1.0.4-SNAPSHOT-MODEL-CORE</version>
</dependency>
<dependency>
<groupId>io.vavr</groupId>
<artifactId>vavr</artifactId>
<version>0.9.2</version>
<scope>test</scope>
</dependency>
Jackson is mainly used for verifying and formatting the output JSON.
Below is the Java code I used:
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.common.io.Files;
import io.vavr.API;
import io.vavr.collection.Array;
import java.io.IOException;
import java.io.PrintWriter;
import java.io.StringWriter;
import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.math.BigDecimal;
import java.nio.charset.StandardCharsets;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.OffsetDateTime;
import java.time.format.DateTimeFormatter;
import java.util.*;
import java.util.stream.Collectors;
/**
* Sample utility for generating dummy JSON sample code from a JAva class directly.
*/
public class GenerateJSONFromClasses {
private static final Random R = new Random();
/**
* Used to avoid infinite loops.
*/
private static final Map<Class<?>, Integer> visited = new HashMap<>();
private static final ObjectMapper mapper = new ObjectMapper();
public static void main(String[] args) throws IOException {
Class<Reservation> clazz = Reservation.class;
generateDummyJSON(clazz, args);
}
public static void generateDummyJSON(Class<Reservation> clazz, String... paths) throws IOException {
StringWriter out = new StringWriter();
try (PrintWriter writer = new PrintWriter(out)) {
writer.println(printObj(clazz));
JsonNode jsonNode = mapper.readTree(out.toString());
String prettyJson = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonNode);
if (paths == null || paths.length == 0) {
System.out.println(prettyJson);
} else {
Array.of(paths).map(sPath -> Paths.get(sPath))
.map(Path::toFile)
.map(API.unchecked(file -> {
Files.write(prettyJson, file, StandardCharsets.UTF_8);
return file;
}));
}
}
}
private static String printObj(Class<?> clazz) {
if (!visited.containsKey(clazz) || visited.get(clazz) <= 1) {
visited.merge(clazz, 1, (integer, integer2) -> integer + integer2);
Field[] declaredFields = clazz.getDeclaredFields();
return "{" +
Array.of(declaredFields).map(field -> String.format(" \"%s\" : %s%n", field.getName(), printFieldValue(field)))
.collect(Collectors.joining(String.format(",%n"))) +
"}";
}
return "";
}
private static Object printFieldValue(Field field) {
Class<?> fieldType = field.getType();
if (String.class.equals(fieldType)) {
return String.format("\"%s\"", field.getName());
} else if (Integer.class.equals(fieldType)) {
return R.nextInt(99) + 1;
} else if (LocalDate.class.equals(fieldType)) {
return String.format("\"%s\"", LocalDate.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd")));
} else if (LocalDateTime.class.equals(fieldType)) {
return String.format("\"%s\"", LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss")));
} else if (OffsetDateTime.class.equals(fieldType)) {
return String.format("\"%s\"", LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss")));
} else if (Date.class.equals(fieldType)) {
return System.currentTimeMillis();
} else if (List.class.equals(fieldType)) {
ParameterizedType parameterizedType = (ParameterizedType) field.getGenericType();
Class<?> clazz = (Class<?>) parameterizedType.getActualTypeArguments()[0];
return String.format("[%s]", printObj(clazz));
} else if (fieldType.isAssignableFrom(Number.class)) {
return R.nextDouble() * 10.0;
} else if (BigDecimal.class.equals(fieldType)) {
return new BigDecimal(R.nextDouble() * 10.0);
} else if (Boolean.class.equals(fieldType)) {
return R.nextBoolean();
} else {
return printObj(fieldType);
}
}
}
