JSON reader and writer for Java.

Notable features, differences.

• Strict compliance with JSON spec
• Correct, useful error messages
• Supports POJOs, Maps, Lists
• Only supports public fields, no JavaBeans or accessors
• No annotations
• Hand coded LA(1) style parser
• Small library (~40kb)
• Requires JDK's JavaCompiler (tools.jar) at runtime
• Code generate POJO from JSON
• Slower than Jackson + Afterburner, faster than JsonBeans

Reader

JSONReader inputs JSON and emits Java objects. You supply the class to instantiate. Must be a concrete subclass of either Map, List, or your own POJO.

import jsonacious.JSONReader;
import java.util.Map;

...

JSONReader jsonReader = new JSONReader();
String json = "{ 'A' : 'apple', 'B' : {} }".replace( '\'', '"' );
HashMap map = jsonReader.parse( json, HashMap.class );
System.out.println( map );

Outputs this, using method HashMap.toString():

{A=apple, B={}}

JSONReader instances are reuseable, but are not thread-safe.

Writer

JSONWriter inputs Java objects (Maps, Lists, POJOs) and emits JSON.

JSONWriter instances are reuseable, but are not thread-safe.

The Rules

JSONacious supports public fields. Non-public, final, static, transient, volatile fields are ignored.

Field types must be instantiable or primitive (scalar). Interfaces and abstract classes are ignored.

class ExamplePOJO 
{
    // Supported
    public String      example1;
    public int         example2;
    public Integer     example3;
    public HashMap     example4;
    public ExamplePOJO example5;
    
    // Ignored
    String                  example6;
    public final String     example7;
    public static String    example8;
    public transient String example9;
    public volatile String  example10;
    public Map              example11; // interface
    public AbstractMap      example12; // abstract class
    
}

Java field names and JSON keys must match exactly; there is no mapping.

Arrays are not supported. Enums will likely be supported. Special handling for Dates might happen.

Generator

POJOnacious converts example JSON data to Java class source code. JSON keys become Java fields, JSON values become Java default field values.

Reflector

(Say something here about runtime in-memory JavaCompiler.)

Customization

Subclasses of Reflector can be registered manually. Capture the generated source code, add it to your project, tweak as needed.

TODO

• Maven (blech)
• Support arrays (maybe).
• Support Dates (maybe).
• Figure out how to debug runtime generated Reflectors.
• Command line utility to generate POJOs from example JSON.
• Command line utility to generate Reflectors (eg during build).