This project is an implementation of the JSON Schema Core Draft v4 specification. It uses the org.json API for representing JSON data.

Add the following to your pom.xml:

<dependency>
    <groupId>org.everit.json</groupId>
    <artifactId>org.everit.json.schema</artifactId>
    <version>1.1.0</version>
</dependency>

import org.everit.json.schema.Schema;
import org.everit.json.schema.loader.SchemaLoader;
import org.json.JSONObject;
import org.json.JSONTokener;
// ...
try (InputStream inputStream = getClass().getResourceAsStream("/path/to/your/schema.json")) {
  JSONObject rawSchema = new JSONObject(new JSONTokener(inputStream));
  Schema schema = SchemaLoader.load(rawSchema);
  schema.validate(new JSONObject("{\"hello\" : \"world\"}")); // throws a ValidationException if this object is invalid
}

Starting from version 1.1.0 the validator collects every schema violations (instead of failing immediately on the first one). Each failure is denoted by a JSON pointer, pointing from the root of the document to the violating part. If more than one schema violations have been detected, then a ValidationException will be thrown at the most common parent elements of the violations, and each separate violations can be obtained using the ValidationException#getCausingExceptions() method.

To demonstrate the above concepts, lets see an example. Lets consider the following schema:

{
	"type" : "object",
	"properties" : {
		"rectangle" : {"$ref" : "#/definitions/Rectangle" }
	},
	"definitions" : {
		"size" : {
			"type" : "number",
			"minimum" : 0
		},
		"Rectangle" : {
			"type" : "object",
			"properties" : {
				"a" : {"$ref" : "#/definitions/size"},
				"b" : {"$ref" : "#/definitions/size"}
			}
		}
	}
}

The following JSON document has only one violation against the schema (since "a" cannot be negative):

{
	"rectangle" : {
		"a" : -5,
		"b" : 5
	}
}

In this case the thrown ValidationException will point to #/rectangle/a and it won't contain sub-exceptions:

try {
  schema.validate(rectangleSingleFailure);
} catch (ValidationException e) {
  // prints #/rectangle/a: -5.0 is not higher or equal to 0
  System.out.println(e.getMessage()); 
}

Now - to illustrate the way how multiple violations are handled - lets consider the following JSON document, where both the "a" and "b" properties violate the above schema:

{
	"rectangle" : {
		"a" : -5,
		"b" : "asd"
	}
}

In this case the thrown ValidationException will point to #/rectangle, and it has 2 sub-exceptions, pointing to #/rectangle/a and #/rectangle/b :

try {
  schema.validate(rectangleMultipleFailures);
} catch (ValidationException e) {
  System.out.println(e.getMessage());
  e.getCausingExceptions().stream()
      .map(ValidationException::getMessage)
      .forEach(System.out::println);
}

This will print the following output:

#/rectangle: 2 schema violations found
#/rectangle/a: -5.0 is not higher or equal to 0
#/rectangle/b: expected type: Number, found: String