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JSON in Java [package org.json]

Maven Central

Click here if you just want the latest release jar file.

Overview

JSON is a light-weight language-independent data interchange format.

The JSON-Java package is a reference implementation that demonstrates how to parse JSON documents into Java objects and how to generate new JSON documents from the Java classes.

Project goals include:

  • Reliable and consistent results
  • Adherence to the JSON specification
  • Easy to build, use, and include in other projects
  • No external dependencies
  • Fast execution and low memory footprint
  • Maintain backward compatibility
  • Designed and tested to use on Java versions 1.6 - 1.11

The files in this package implement JSON encoders and decoders. The package can also convert between JSON and XML, HTTP headers, Cookies, and CDL.

The license includes this restriction: "The software shall be used for good, not evil." If your conscience cannot live with that, then choose a different package.

If you would like to contribute to this project

Bug fixes, code improvements, and unit test coverage changes are welcome! Because this project is currently in the maintenance phase, the kinds of changes that can be accepted are limited. For more information, please read the FAQ.

Build Instructions

The org.json package can be built from the command line, Maven, and Gradle. The unit tests can be executed from Maven, Gradle, or individually in an IDE e.g. Eclipse.

Building from the command line

Build the class files from the package root directory src/main/java

javac org\json\*.java

Create the jar file in the current directory

jar cf json-java.jar org/json/*.class

Compile a program that uses the jar (see example code below)

javac -cp .;json-java.jar Test.java 

Test file contents

import org.json.JSONObject;
public class Test {
    public static void main(String args[]){
       JSONObject jo = new JSONObject("{ \"abc\" : \"def\" }");
       System.out.println(jo.toString());
    }
}

Execute the Test file

java -cp .;json-java.jar Test

Expected output

{"abc":"def"}

Tools to build the package and execute the unit tests

Execute the test suite with Maven:

mvn clean test

Execute the test suite with Gradlew:

gradlew clean build test

Notes

Recent directory structure change

Due to a recent commit - #515 Merge tests and pom and code - the structure of the project has changed from a flat directory containing all of the Java files to a directory structure that includes unit tests and several tools used to build the project jar and run the unit tests. If you have difficulty using the new structure, please open an issue so we can work through it.

Implementation notes

Numeric types in this package comply with ECMA-404: The JSON Data Interchange Format and RFC 8259: The JavaScript Object Notation (JSON) Data Interchange Format. This package fully supports Integer, Long, and Double Java types. Partial support for BigInteger and BigDecimal values in JSONObject and JSONArray objects is provided in the form of get(), opt(), and put() API methods.

Although 1.6 compatibility is currently supported, it is not a project goal and might be removed in some future release.

In compliance with RFC8259 page 10 section 9, the parser is more lax with what is valid JSON then the Generator. For Example, the tab character (U+0009) is allowed when reading JSON Text strings, but when output by the Generator, the tab is properly converted to \t in the string. Other instances may occur where reading invalid JSON text does not cause an error to be generated. Malformed JSON Texts such as missing end " (quote) on strings or invalid number formats (1.2e6.3) will cause errors as such documents can not be read reliably.

Some notable exceptions that the JSON Parser in this library accepts are:

  • Unquoted keys { key: "value" }
  • Unquoted values { "key": value }
  • Unescaped literals like "tab" in string values { "key": "value with an unescaped tab" }
  • Numbers out of range for Double or Long are parsed as strings

Recent pull requests added a new method putAll on the JSONArray. The putAll method works similarly to other put methods in that it does not call JSONObject.wrap for items added. This can lead to inconsistent object representation in JSONArray structures.

For example, code like this will create a mixed JSONArray, some items wrapped, others not:

SomeBean[] myArr = new SomeBean[]{ new SomeBean(1), new SomeBean(2) };
// these will be wrapped
JSONArray jArr = new JSONArray(myArr);
// these will not be wrapped
jArr.putAll(new SomeBean[]{ new SomeBean(3), new SomeBean(4) });

For structure consistency, it would be recommended that the above code is changed to look like 1 of 2 ways.

Option 1:

SomeBean[] myArr = new SomeBean[]{ new SomeBean(1), new SomeBean(2) };
JSONArray jArr = new JSONArray();
// these will not be wrapped
jArr.putAll(myArr);
// these will not be wrapped
jArr.putAll(new SomeBean[]{ new SomeBean(3), new SomeBean(4) });
// our jArr is now consistent.

Option 2:

SomeBean[] myArr = new SomeBean[]{ new SomeBean(1), new SomeBean(2) };
// these will be wrapped
JSONArray jArr = new JSONArray(myArr);
// these will be wrapped
jArr.putAll(new JSONArray(new SomeBean[]{ new SomeBean(3), new SomeBean(4) }));
// our jArr is now consistent.

Unit Test Conventions

Test filenames should consist of the name of the module being tested, with the suffix "Test". For example, Cookie.java is tested by CookieTest.java.

The fundamental issues with JSON-Java testing are:

  • JSONObjects are unordered, making simple string comparison ineffective.
  • Comparisons via equals() is not currently supported. Neither JSONArray nor JSONObject override hashCode() or equals(), so comparison defaults to the Object equals(), which is not useful.
  • Access to the JSONArray and JSONObject internal containers for comparison is not currently available.

General issues with unit testing are:

  • Just writing tests to make coverage goals tends to result in poor tests.
  • Unit tests are a form of documentation - how a given method works is demonstrated by the test. So for a code reviewer or future developer looking at code a good test helps explain how a function is supposed to work according to the original author. This can be difficult if you are not the original developer.
  • It is difficult to evaluate unit tests in a vacuum. You also need to see the code being tested to understand if a test is good.
  • Without unit tests, it is hard to feel confident about the quality of the code, especially when fixing bugs or refactoring. Good tests prevent regressions and keep the intent of the code correct.
  • If you have unit test results along with pull requests, the reviewer has an easier time understanding your code and determining if it works as intended.

Files

JSONObject.java: The JSONObject can parse text from a String or a JSONTokener to produce a map-like object. The object provides methods for manipulating its contents, and for producing a JSON compliant object serialization.

JSONArray.java: The JSONArray can parse text from a String or a JSONTokener to produce a vector-like object. The object provides methods for manipulating its contents, and for producing a JSON compliant array serialization.

JSONTokener.java: The JSONTokener breaks a text into a sequence of individual tokens. It can be constructed from a String, Reader, or InputStream. It also can parse text from a String, Number, Boolean or null like "hello", 42, true, null to produce a simple json object.

JSONException.java: The JSONException is the standard exception type thrown by this package.

JSONPointer.java: Implementation of JSON Pointer (RFC 6901). Supports JSON Pointers both in the form of string representation and URI fragment representation.

JSONPropertyIgnore.java: Annotation class that can be used on Java Bean getter methods. When used on a bean method that would normally be serialized into a JSONObject, it overrides the getter-to-key-name logic and forces the property to be excluded from the resulting JSONObject.

JSONPropertyName.java: Annotation class that can be used on Java Bean getter methods. When used on a bean method that would normally be serialized into a JSONObject, it overrides the getter-to-key-name logic and uses the value of the annotation. The Bean processor will look through the class hierarchy. This means you can use the annotation on a base class or interface and the value of the annotation will be used even if the getter is overridden in a child class.

JSONString.java: The JSONString interface requires a toJSONString method, allowing an object to provide its own serialization.

JSONStringer.java: The JSONStringer provides a convenient facility for building JSON strings.

JSONWriter.java: The JSONWriter provides a convenient facility for building JSON text through a writer.

CDL.java: CDL provides support for converting between JSON and comma delimited lists.

Cookie.java: Cookie provides support for converting between JSON and cookies.

CookieList.java: CookieList provides support for converting between JSON and cookie lists.

HTTP.java: HTTP provides support for converting between JSON and HTTP headers.

HTTPTokener.java: HTTPTokener extends JSONTokener for parsing HTTP headers.

XML.java: XML provides support for converting between JSON and XML.

JSONML.java: JSONML provides support for converting between JSONML and XML.

XMLTokener.java: XMLTokener extends JSONTokener for parsing XML text.

Release history:

JSON-java releases can be found by searching the Maven repository for groupId "org.json" and artifactId "json". For example: https://search.maven.org/search?q=g:org.json%20AND%20a:json&core=gav

20210307    Recent commits and potentially breaking fix to JSONPointer

20201115    Recent commits and first release after project structure change

20200518    Recent commits and snapshot before project structure change

20190722    Recent commits

20180813    POM change to include Automatic-Module-Name (#431)

20180130    Recent commits

20171018    Checkpoint for recent commits.

20170516    Roll up recent commits.

20160810    Revert code that was breaking opt*() methods.

20160807    This release contains a bug in the JSONObject.opt*() and JSONArray.opt*() methods,
it is not recommended for use.
Java 1.6 compatability fixed, JSONArray.toList() and JSONObject.toMap(),
RFC4180 compatibility, JSONPointer, some exception fixes, optional XML type conversion.
Contains the latest code as of 7 Aug 2016

20160212    Java 1.6 compatibility, OSGi bundle. Contains the latest code as of 12 Feb 2016.

20151123    JSONObject and JSONArray initialization with generics. Contains the latest code as of 23 Nov 2015.

20150729    Checkpoint for Maven central repository release. Contains the latest code
as of 29 July 2015.