This feature is available in a current snapshot: 3.0-SNAPSHOT for Java 16 and up.

While ActiveWeb can process validations of simple classes as described here, often modern apps whether they are APIs or backends for a single page app require a complex JSON structure. Such structures might be deeper than a single level. In such cases, you can use the JavaLite JSON capability that allows you to map a variable structure JSON object to a class JSONBase. The page JSON describes basic JSONBase features. However, the current page dives deeper into JSON processing and validation in the context of a web requests.

The class JSONBase has two powerful features:

  • It extends the ValidationSupport class that makes the entire Validation system available to subclasses.
  • It provides the JSON Deep Path feature.

In addition, the ActiveWeb does an implicit validation of any object whose class extends JSONBase.

Example JSON Processing

Let's say we have a web client (a browser, or an API client) post this JSON document in a web request:

A simple class for encapsulating this JSON object might look like this:

A controller would look like this:

By the time the action method saveStudents is called, the UniversityRequest a JSON request was already parsed and passed into the method.

JSON Validation

The class UniversityRequest above extends from JSONBase, which provides various validations in the same way the general Validations framework as well as JSON Validations operate.

Let's enhance the class UniversityRequest with a single validation:

The last line in the constructor above will validate that the structure of JSON will have a JSON Array (or Java List) at the path "university.students". A controller would look a bit more elaborate:

As you can see, the ActiveWeb framework does most of the heavy lifting of parsing and verifying the incoming JSON requests.

JSON Validators

There many other validators in the package org.javalite.json


Just as above, will validate that the structure at the path "university.students" is a list.


Will validate that the structure at the path "university" is a map.


Will validate that the structure at the path "" is a boolean.

another take on the boolean: will expect a pre-defined value:

Standard validators

Since the class JSONBase ties into standard Validation framework, you can use any standard validation in addition. Here is an example:

as you can see, the twist that JSONBase adds is a Deep Path to a value in a JSON document.

Custom validator

If none of the existing validators work for you, you can implement a custom one:

As you can see, writing a custom validator is not complicated.

How to comment

The comment section below is to discuss documentation on this page.

If you have an issue, or discover bug, please follow instructions on the Support page