Coffee break #175. How can we read a JSON file in Java? What is Java Development Kit (JDK)?

How can we read a JSON file in Java?

Source: DZone JSON is a simple format for storing and sending data to a web page. It is commonly used in JavaScript, but today we will learn how to work with it in Java.

Reading a JSON file in Java

To learn about reading a JSON file in Java, first we need to understand what a JSON file is. JSON is an acronym for “JavaScript Object Notation”. JSON can be used to send data from a server to a web page. This means that it is used in web development. It is important to remember:

• JSON is a text file, so it can be easily transferred.
• JSON is not language specific.

Syntax

The data in the JSON file must be in the format of name/value pairs, with commas separating the different data. Curly braces are used to store objects, and square brackets are used to store arrays.

JSON Features

Below are some features of JSON:

• Simple.
• Has an independent platform.
• Easy to convey.
• Supports extensibility.
• Availability of compatibility.

Data types

Data types specific to JSON:

• String - The string is represented inside quotes.
• Number - Represents numeric characters.
• Boolean – consists of either true or false.
• Null – empty.

JSON in Java

To use JSON in Java, we must use the json.simple library for encoding and decoding. To run the JSON program and set the classpath, you need to install the jar (Java archive) json.simple. Data structures used in JSON:

• JSON objects;
• JSON arrays.

JSON objects

JSON objects are represented between curly braces. Objects must be in key/value pairs. The key is represented as a String and the values ​​represent any of the data types mentioned above. Example:

Key, value pairs - {"Name": "Kotte"}

JSON arrays

JSON arrays are used to store objects. These objects are enclosed in square brackets []. Example:

[{

"Name" : "Kotte",

"College" : "BVRIT"

"Branch" : "Computer Science Engineering",

"Section" : "CSE_C"

},

{

"Name" : "Saikiran",

"College" : "BVRIT"

"Branch" : "Computer Science Engineering",

"Section" : "CSE_C"



}]

In the above example, the student details are represented as an array and inside the array, the student data is stored as objects.

Simple JSON Program in Java

import org.json.simple.JSONObject;

public class Json

{

            public static void main(String args[])

            {

                        JSONObject j = new JSONObject();

                        j.put("Name", "Kotte");

                        j.put("College", "BVRIT");

                        j.put("Branch" , "Computer science engineering");

                        j.put("Section", "CSE-C");

                        System.out.println(j);

}

}

Conclusion:

Reading a JSON file in Java

To read a JSON file in Java, you need to use the FileReader() method. Example:

{

            "name" : "Kotte",

            "college" : "BVRIT"

}

The above code is the file that is used to read. We are using the json.simple library .

//program for reading a JSON file

import org.json.simple.JSONArray;

import org.json.simple.JSONObject;

import org.json.simple.parser.*;



public class JSON

{

            public static void main(Strings args[])

            {

                        // file name is File.json

                        Object o = new JSONParser().parse(new FileReader(File.json));

                        JSONObject j = (JSONObject) o;

                        String Name = (String) j.get("Name");

                        String College = (String ) j.get("College");



                        System.out.println("Name :" + Name);

                        System.out.println("College :" +College);

}

}

Conclusion: This program uses JSONParser().parse() which is present in org.json.simple.parser.* to parse the File.json file.

What is Java Development Kit (JDK)?

Source: Medium This post will introduce you to the workings and uses of the Java Development Kit. In their work, programmers often use the Java Development Kit, known as the JDK. It is a cross-platform set of tools and libraries for creating Java-based software applications and applets. The JDK includes both the Java Virtual Machine (known as the JVM) and the Java Runtime Environment (known as the JRE). The JDK also includes the javac compiler, performance monitoring tools, a debugger, standard Java class libraries, examples, documentation, and various utilities. The Java Development Kit (JDK) is developed by Oracle Corporation. Its product implements JVMS, JLS and Java API SE (API). In addition to the commercial version, Oracle introduced a free version of the OpenJDK package to the market. There are also alternative JDKs from other companies in the Java development market. If the only thing you want to do on your computer is run Java applications, then you don't need to worry about the differences between the Java Runtime Environment (JRE) and the Java Development Kit (JDK). However, you will need the Java Development Kit (JDK) to create Java-based software. The Java Runtime Environment (JRE) included with the JDK is called the Private Runtime. This environment differs from the standard JRE in that it includes additional components. It also gives developers access to the Java Virtual Machine (JVM) and all class libraries used in production environments, in addition to internationalization and IDL libraries.

Most Popular JDKs

In addition to JDK and OpenJDK from Oracle, developers should pay attention to other versions of the package:

• Azul Systems Zing : A high-performance, low-latency Java virtual machine for Linux.
• Azul Systems (for Linux, Windows, Mac OS X and IBM J9 JDK: for AIX, Linux, Windows and many other operating systems).
• Amazon Corretto (OpenJDK and long-term support included).

Compile and run Java code using the JDK

You can create an executable Java program from a text file using the JDK compiler. When compiled, your Java code is converted into bytecode with a .class extension . First, you need to create a Java text file and save it with a unique name. In this case, we save Hello.java as the file name. Then run the Java compilation tool with the javac command and you're done. To avoid receiving an error message such as “The system cannot locate a path supplied,” you must provide the full path to your Java text file. Hello is the file name, and the full path to the file is preceded by Hello in the following command example. The path and executable for javac.exe must be enclosed in quotes. Now that Hello.class is created, you can see it in the same directory as Hello.java , which is very convenient. Now you can execute your code by simply typing java hello in your terminal. Keep in mind that running your code does not require including a .class file.

Jar Component

The JDK includes many important tools. Apart from javac, the most commonly used tool is jar. It contains nothing more than a set of Java classes. Once the .class files are ready, you can package them and save them in an archive known as a “jar”. After this, the jar file can be run in the mobile environment (Android).