Java JSON Parser

This Java library provides a JSON parser. The parser reads a JSON text, parses it in accordance with RFC 8259 and creates a corresponding data structure with Java objects.

The main feature of this library is that it keeps the original JSON text information in the Java objects. Therefore, for example, your application can show where exactly (line number & column number) the JSON text has a problem if there is a semantic error.

If the given JSON text includes a syntax error, this library shows an error message with line and column numbers so that the users will be able to know where exactly the problem is. This library is suitable to parse configuration files in JSON that the users manually write. The error message can be customized by option switches. See parser error handling options for more details.

Setup

Add the following dependency to your build file:

Maven
<dependency>
  <groupId>com.github.tnakamot</groupId>
  <artifactId>json-parser</artifactId>
  <version>0.2.1</version>
</dependency>
Gradle
dependencies {
  compile group: 'com.github.tnakamot', name: 'json-parser', version: '0.2.1'
}
sbt
libraryDependencies += "com.github.tnakamot" % "json-parser" % "0.2.1"

Usage

Import the following packages in your Java source code.

import com.github.tnakamot.json.JSONText;
import com.github.tnakamot.json.value.*;

Then, instantiate JSONText and call parse(). root().

JSONText jsText = JSONText.fromString(
        " { \"key1\": \"value\", " +
        "   \"key2\": 1.53, " +
        "   \"key3\": true," +
        "   \"key4\": null } ");
JSONValue root = jsText.parse().root();

The root JSON value can be obtained as an instance of JSONValue.

Typically, the type of the root JSON value is “object”. Check the type of the root value, and cast it to JSONValueObject. Then, you will be able to get values as shown below.

if (root.type() == JSONValueType.OBJECT) {
    JSONValueObject rootObject = (JSONValueObject) root;

    JSONValue value1 = rootObject.get("key1");
    if (value1.type() == JSONValueType.STRING) { 
        String value1Str = ((JSONValueString) value1).value();
        System.out.println(value1Str);
    }

    JSONValue value2 = rootObject.get("key2");
    if (value2.type() == JSONValueType.NUMBER) { 
        double value2Dbl = ((JSONValueNumber) value2).toDouble();
        System.out.println(value2Dbl);
    }

    JSONValue value3 = rootObject.get("key3");
    if (value3.type() == JSONValueType.BOOLEAN) {
        boolean value3Bool = ((JSONValueBoolean) value3).value();
        System.out.println(value3Bool);
    }

    JSONValue value4 = rootObject.get("key4");
    if (value4.type() == JSONValueType.NULL) {
        System.out.println("null");
    }
}

Convenience methods

If you already know the data structure and data types exactly, your Java program call convenience methods getXxxx() like shown below.

JSONText jsText = JSONText.fromString(
        " { \"key1\": \"value\", " +
        "   \"key2\": 3.14, " +
        "   \"key3\": false," +
        "   \"key4\": 1024," +
        "   \"key5\": [5, 1, 2], "+
        "   \"key6\": {\"key6-1\": 0} }");
JSONValueObject root = (JSONValueObject) jsText.parse().root();

String  value1Str = root.getString("key1");
System.out.println(value1Str);

double value2Dbl = root.getDouble("key2");
System.out.println(value2Dbl);

boolean value3Bool = root.getBoolean("key3");
System.out.println(value3Bool);

long value4Lng = root.getLong("key4");
System.out.println(value4Lng);

JSONValueArray value5Arr = root.getArray("key5");
System.out.println(value5Arr.getLong(0));
System.out.println(value5Arr.getLong(1));
System.out.println(value5Arr.getLong(2));

JSONValueObject value6Obj = root.getObject("key6");
System.out.println(value6Obj.getLong("key6-1"));
0.2.1