jsonschemafriend

jsonschemafriend is a JSON Schema loader and validator, delivered as a Java library. Since version 0.10.0, schemas and objects are received in the form of standard Java objects, making it compatible with major Java JSON parsers such as org.json, gson and Jackson.

About

An online demonstration is here.

It is written by jimblackler@gmail.com and offered under an Apache 2.0 license.

It is compatible with the following metaschemas

Including in a project

The library is live on JitPack.

Gradle

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'
    // ...
}

Maven

<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>

Usage

Javadocs can be found here.

Format

The library follows the convention that has emerged for JSON document handling in Java, where instead of custom classes to represent documents and subdocuments, a tree of basic Java interfaces is used. Code that processes documents in this convention (rather than through libary-specific wrapper classes such as org.json's JSONObject) are not tied to any one JSON library. 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.

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:

org.json

new JSONObject(jsonString).toMap()
gson

new Gson().fromJson(jsonString, Map.class);
Jackson

new ObjectMapper().readValue(jsonString, Map.class);
usejson

new Json5Parser().parse(jsonString);

Via a Map

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", "http://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();
    }
  }
}

Via a JSONObject

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", "http://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();
    }
  }
}

Via Java Resources

This example loads a schema in the resources folder and validates data in the resources folder.

`schema.json`

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "properties": {
    "name": {
      "type": "string",
      "minLength": 2
    }
  }
}

`data1.json`

{
  "name": "Bill"
}

`data2.json`

{
  "name": ""
}

`Main.java`

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();
    }
  }
}

From URIs or URLs

This example loads both the schema, and the data to test from the internet, via URIs (URLs can also be use).

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();
    }
  }
}

From files

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"));

Custom validation handling.

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();
    }
  }
}

Strict regular expression handling.

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);
  }
}

tayloj/jsonschemafriend