22.9 Json0220: decoding json strings

Revised: Thu Jun 02 19:25:56 CDT 2016

This page is included in the following Books:

• The json-simple Java Library .
• INEW2338 - Advanced Java Programming
• Object-Oriented Programming (OOP) with Java

Table of contents

• Table of contents
• Preface
  • Viewing tip
    • Figures
    • Listings
• General background information
• Discussion and sample code
  • Decode and display using the JSONValue class
  • The method named decodeC
  • Display contents of JSONObject objects
  • Decode and display using the JSONParser class
  • The method named decodeD
  • The end of the program
• Run the program
• Complete program listing
• Miscellaneous

Preface

This is a page from the book titled The json-simple Java Library . The book explains how to use the json-simple Java library to generate, transform, and query JSON text. This page explains how to decode JSON strings using the parsemethods of the JSONValue and JSONParser classes.

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following links to easily find and view the Figuresand Listings while you are reading about them.

Figures

• Figure 1 . Program output.

Listings

• Listing 1 . Decode and display using the JSONValue class.
• Listing 2 . The method named decodeC.
• Listing 3 . The display method.
• Listing 4 . Decode and display using the JSONParser class.
• Listing 5 . The method named decodeD.
• Listing 6 . The program named Code.java.

General background information

As mentioned in the Preface , this page deals with the classes named JSONValue and JSONParser . Each of these classes extends the Object class and provides various methods for processing JSON data. The page also exposes you to the classnamed ParseException .

All of the methods in the JSONValue class are static methods. Methods in this class are available to deal with JSON input data inboth the string format and the JSONObject format.

None of the methods in the JSONParser class are static methods. In general the methods in this class are designed to deal only withinput data in the string format.

Both classes provide several overloaded parse methods that can be used to parse input JSON text from different sources into the JSONObject format.

The sample program that follows will use the parse method from both classes to parse JSON strings into JSONObject objects.

Discussion and sample code

The program named Code (see Listing 6 ) consists of some old code and some new code. The program begins just like theprogram that I explained in the earlier page titled Json0215: Encoding JSON Strings . The beginning portion of the program is used solely to create JSON data instring format and to store the individual strings as elements in an ArrayList object.

This code constructs three JSONObject objects and saves them in an ArrayList object. Then it transforms each JSONObject object into a String object and saves the strings in a second ArrayList object. The new code decodes the strings into JSONObject objects using a parse method from the JSONValue class and saves them in a third ArrayList object.