Hope

Hope is a high level language for predicate evaluation on JSON written in java. It uses jackson for json handling and json-path for value extraction.

Sample Hope expressions/rules

 "$.val" + 2 > 3
 "$.a" + "$.b" <= math.abs("$.c")

Features

• Simple syntax
• Bunch of rich standard library functions built in
• Performant
• Easy to add custom functions

Getting started

Hope in deployed in clojure maven repository. To use hope, please add the following to <repository/> section of your pom.xml file.

        <repository>
            <id>clojars</id>
            <name>Clojars repository</name>
            <url>https://clojars.org/repo</url>
        </repository>

Maven dependency

Use the following dependency in your code.

    <dependency>
        <groupId>io.appform.hope</groupId>
        <artifactId>hope-lang</artifactId>
        <packaging>pom</packaging>
        <version>1.0.4</version>
    </dependency>

Basic usage

The following steps can be used to parse and evaluate a predicate expression or rule.

Create HopeLangEngine

The main class you need to know is HopeLangEngine. To use this class use the provided builder.

    final HopeLangEngine hope = HopeLangEngine.builder()
                                .build();

Note: Creation of this class is a time consuming affair. Create and resue this. This class is thread-safe.

Evaluate an expression

The following code snippet evaluates an expression against a parsed jackson Json node.

    final JsonNode root = new ObjectMapper().readTree("{\"val\" : 10 }");
    final String expr = " \"$.val\" + 2 > 9";
    if(engine.evaluate(expr, root)) {
        ...
    }

For real life use cases, rule should be parsed only once and cached. Same cached rule can be evaluated multiple times by passing different payloads. See wiki for more details.

Documentation

Please go through the hope wiki for detailed documentation

License

Hope is licensed under Apache License Version 2.0