SJForms (Simple Java Forms)

This is a small declarative-style library for validating untrusted input in Java. It is useful for checking HTTP request parameters, command-line parameters, etc.

Usage is fairly straightforward. First declare the structure of your form (usually as static class members):

Field<String> INPUT_FIELD = Field.stringField("input");
Field<Integer> LIMIT_FIELD = Field.intField("limit").required();
Form FORM = new Form(INPUT_FIELD, LIMIT_FIELD);

Next load some input and validate it:

// somehow acquire a Map<String, String> (from field names to input values) called inputMap

ParseResult parseResult;
try {
  parseResult = FORM.parse(inputMap);
} catch (ValidationException e) {
  System.err.println("Input validation failed with message: " + e.getMessage());
  return;
}

String input = parseResult.getParsedValue(INPUT_FIELD);
int limit = parseResult.getParsedValue(LIMIT_FIELD);

If the Form/ParseResult API is too heavy-handed for you, you can just use the Field objects to validate data directly:

// somehow acquire a String called limitString

int limit;
try {
  limit = LIMIT_FIELD.validate(limitString);
} catch (ValidationException e) {
  System.err.println("Input validation failed with message: " + e.getMessage());
  return;
}

The library is totally threadsafe (i.e. the same Forms, Fields, and other classes can be used from multiple threads concurrently).

Building

This project uses the Gradle build system. It was made using Gradle 2.0, but the build files are very simple and earlier/later versions of Gradle should work just fine. To build:

$ gradle build

This will generate jar files in build/libs and examples/build/libs. You can also generate javadoc with Gradle:

$ gradle javadoc