jsonschemafriend is a JSON Schema loader and validator, delivered as a Java library.
An online demonstration is here.
It is written by [email protected] and offered under an Apache 2.0 license.
It is compatible with the following metaschemas
- https://json-schema.org/draft-03/schema#
- https://json-schema.org/draft-04/schema#
- https://json-schema.org/draft-06/schema#
- https://json-schema.org/draft-07/schema#
- https://json-schema.org/draft/2019-09/schema
The library is live on JitPack.
To include in a Gradle project, ensure jitpack repository is specified in your
base build.gradle file. For example:
repositories {
maven {
url 'https://jitpack.io'
}
// ...
}Add the project as a dependency in the module's build.gradle.
dependencies {
implementation 'net.jimblackler.jsonschemafriend:core:0.10.5'
// ...
}<repositories>
<repository>
<id>jitpack.io</id>
<url>https://jitpack.io</url>
</repository>
</repositories><dependency>
<groupId>net.jimblackler</groupId>
<artifactId>jsonschemafriend</artifactId>
<version>0.10.0</version>
</dependency>Javadocs can be found here.
The library is "BYOP"; Bring Your Own Parser. Schemas and objects are received not as JSON strings but in the form of standard Java objects, making it compatible with all major Java JSON parsers.
This enables the selection of a JSON parser by the client, based on preferences such as speed, handling of numbers, and handling of key order, all of which vary between libraries. Clients can also chose to construct these document directly or on import from different formats such as JSON5 and YAML. It also makes it easier to validate documents before serialization.
The parser takes documents and schemas as a tree of objects, typed as follows:
| JSON value | Java class |
|---|---|
| object | java.util.Map<String, Object> |
| array | java.util.List<Object> |
| number | java.lang.Number |
| string | java.lang.String |
| true/false | java.lang.Boolean |
| null | null |
Documents arranged this way can be created by all major JSON libraries for Java, including:
-
new JSONObject(jsonString).toMap() -
new Gson().fromJson(jsonString, Map.class); -
new ObjectMapper().readValue(jsonString, Map.class); -
new Json5Parser().parse(jsonString);
This is an example of loading a schema in a Map.
import net.jimblackler.jsonschemafriend.Schema;
import net.jimblackler.jsonschemafriend.SchemaException;
import net.jimblackler.jsonschemafriend.SchemaStore;
import net.jimblackler.jsonschemafriend.Validator;
import java.util.HashMap;
import java.util.Map;
public class Main {
public static void main(String[] args) {
// Create a new schema in a map.
Map<String, Object> schemaMap = new HashMap<>();
schemaMap.put("$schema", "https://json-schema.org/draft-07/schema#");
schemaMap.put("type", "integer");
try {
SchemaStore schemaStore = new SchemaStore(); // Initialize a SchemaStore.
Schema schema = schemaStore.loadSchema(schemaMap); // Load the schema.
Validator validator = new Validator(); // Create a validator.
validator.validate(schema, 1); // Will not throw an exception.
validator.validate(schema, "x"); // Will throw a ValidationException.
} catch (SchemaException e) {
e.printStackTrace();
}
}
}This is an example of loading a schema in a JSONObject using
JSONObject.toMap().
import net.jimblackler.jsonschemafriend.Schema;
import net.jimblackler.jsonschemafriend.SchemaException;
import net.jimblackler.jsonschemafriend.SchemaStore;
import net.jimblackler.jsonschemafriend.Validator;
import org.json.JSONObject;
public class Main {
public static void main(String[] args) {
// Create a new schema in a JSON object.
JSONObject schemaJson = new JSONObject();
schemaJson.put("$schema", "https://json-schema.org/draft-07/schema#");
schemaJson.put("type", "integer");
try {
SchemaStore schemaStore = new SchemaStore(); // Initialize a SchemaStore.
Schema schema = schemaStore.loadSchema(schemaJson.toMap()); // Load the schema.
Validator validator = new Validator(); // Create a validator.
validator.validate(schema, 1); // Will not throw an exception.
validator.validate(schema, "x"); // Will throw a ValidationException.
} catch (SchemaException e) {
e.printStackTrace();
}
}
}This example loads a schema in the resources folder and validates data in the
resources folder.
{
"$schema": "https://json-schema.org/draft-07/schema#",
"properties": {
"name": {
"type": "string",
"minLength": 2
}
}
}{
"name": "Bill"
}{
"name": ""
}import java.io.IOException;
import net.jimblackler.jsonschemafriend.Schema;
import net.jimblackler.jsonschemafriend.SchemaException;
import net.jimblackler.jsonschemafriend.SchemaStore;
import net.jimblackler.jsonschemafriend.Validator;
public class Main {
public static void main(String[] args) {
try {
SchemaStore schemaStore = new SchemaStore(); // Initialize a SchemaStore.
// Load the schema.
Schema schema = schemaStore.loadSchema(Main.class.getResource("/schema.json"));
Validator validator = new Validator();
// Will not throw an exception.
validator.validate(schema, Main.class.getResourceAsStream("/data1.json"));
// Will throw a ValidationException.
validator.validate(schema, Main.class.getResourceAsStream("/data2.json"));
} catch (SchemaException | IOException e) {
e.printStackTrace();
}
}
}This example loads both the schema, and the data to test from the internet, via URIs (URLs can also be used).
import java.io.IOException;
import java.net.URI;
import net.jimblackler.jsonschemafriend.Schema;
import net.jimblackler.jsonschemafriend.SchemaException;
import net.jimblackler.jsonschemafriend.SchemaStore;
import net.jimblackler.jsonschemafriend.Validator;
public class Main {
public static void main(String[] args) {
try {
SchemaStore schemaStore = new SchemaStore(); // Initialize a SchemaStore.
// Load the schema.
Schema schema = schemaStore.loadSchema(URI.create("https://json.schemastore.org/resume"));
URI resume = URI.create(
"https://gist.githubusercontent.com/thomasdavis/c9dcfa1b37dec07fb2ee7f36d7278105/raw");
// Will not throw an exception; document passes the schema.
new Validator().validate(schema, resume);
} catch (SchemaException | IOException e) {
e.printStackTrace();
}
}
}Both schemas and test data can be specified as a java.io.File. For example:
Schema schema = schemaStore.loadSchema(new File("/tmp/schema.json"));
new Validator().validate(schema, new File("/tmp/test.json"));A custom Consumer can be passed to the validator to collect validation errors,
rather than triggering a ValidationException.
import java.net.URI;
import java.util.HashMap;
import java.util.Map;
import net.jimblackler.jsonschemafriend.MissingPropertyError;
import net.jimblackler.jsonschemafriend.Schema;
import net.jimblackler.jsonschemafriend.SchemaException;
import net.jimblackler.jsonschemafriend.SchemaStore;
import net.jimblackler.jsonschemafriend.Validator;
public class Main {
public static void main(String[] args) {
try {
SchemaStore schemaStore = new SchemaStore(); // Initialize a SchemaStore.
// Load the schema.
Schema schema =
schemaStore.loadSchema(URI.create("https://json.schemastore.org/chrome-manifest"));
// Send an object that won't validate, and collect the validation errors.
Map<String, Object> document = new HashMap<>();
new Validator().validate(schema, document, validationError -> {
if (validationError instanceof MissingPropertyError) {
MissingPropertyError missingPropertyError = (MissingPropertyError) validationError;
System.out.println("A missing property was: " + missingPropertyError.getProperty());
}
});
} catch (SchemaException e) {
e.printStackTrace();
}
}
}Strictly ECMA-compliant regular expressions requires an ECMA interpreter, GraalJS. This is fairly heavyweight and is not compatible with Android. For this mode include both the core library and the extra library, and initialize it as shown in the fragment below.
dependencies {
// ...
implementation 'net.jimblackler.jsonschemafriend:core:0.10.5'
implementation 'net.jimblackler.jsonschemafriend:extra:0.10.5'
}import net.jimblackler.jsonschemafriend.CachedRegExPatternSupplier;
import net.jimblackler.jsonschemafriend.Validator;
import net.jimblackler.jsonschemafriendextra.Ecma262Pattern;
public class Main {
public static void main(String[] args) {
Validator validator =
new Validator(new CachedRegExPatternSupplier(Ecma262Pattern::new), validationError -> true);
}
}