Convert JSON to List of map java

It is impossible explicitly, however, you can deserialize you String into List< Object> and then cast your Object in for-loop to Map< String, Object>:

String jsonString = '[{"id":2,"name":"Abc_SS","description":"Abc"},{"id":100,"name":"sales","description":"sales"}]'; List items = [List] JSON.deserializeUntyped[jsonString]; for [Object itemObj : items] { Map item = [Map] itemObj; //now you can work with it like you always work with Map }

In this article, we'll convert a JSON array into a Java Array and Java List using Jackson.

Since we're using Jackson, you'll have to add it to your project. If you're using Maven, it's as easy as adding the dependency:

com.fasterxml.jackson.core jackson-databind 2.11.2

Or, if you're using Gradle:

compile group: 'com.fasterxml.jackson.core', name: 'jackson-databind', version: '2.11.2'

Since we're mapping from JSON to our own objects, let's go ahead and define a POJO:

public class Language { private String name; private String description;

Reading JSON from a String

Let's start out with reading JSON from a String. The String contains an array of programming languages, with brief descriptions:

String json = "[{\"name\": \"Java\", \"description\": \"Java is a class-based, object-oriented programming language.\"},{\"name\": \"Python\", \"description\": \"Python is an interpreted, high-level and general-purpose programming language.\"}, {\"name\": \"JS\", \"description\": \"JS is a programming language that conforms to the ECMAScript specification.\"}]";

Using Jackson's ObjectMapper class, it's easy to read values and map them to an object, or an array of objects. We just use the readValue[] method, passing the JSON contents and the class we'd like to map to. Since we're mapping to an array of Language, we'll also specify this in the readValue[] method:

final ObjectMapper objectMapper = new ObjectMapper[]; Language[] langs = objectMapper.readValue[json, Language[].class];

Alternatively, you can extract the values directly into a list, using Jackson's TypeReference:

List langList = objectMapper.readValue[json, new TypeReference[]{}];

Without using TypeReference, which is advised, you can convert the array into a list with any other approach at your disposal, such as:

List langList = new ArrayList[Arrays.asList[langs]];

And then print out the values:

langList.forEach[x -> System.out.println[x.toString[]]];

This results in:

Language{name='Java', description='Java is a class-based, object-oriented programming language.'} Language{name='Python', description='Python is an interpreted, high-level and general-purpose programming language.'} Language{name='JS', description='JS is a programming language that conforms to the ECMAScript specification.'}

Reading JSON from a File

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We don't always deal with JSON in String format. Oftentimes, the contents come from a File. Thankfully, Jackson makes this task as easy as the last one, we just provide the File to the readValue[] method:

final ObjectMapper objectMapper = new ObjectMapper[]; List langList = objectMapper.readValue[ new File["langs.json"], new TypeReference[]{}]; langList.forEach[x -> System.out.println[x.toString[]]];

The langs.json file contains:

[ { "name": "Java", "description": "Java is a class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible." }, { "name": "Python", "description": "Python is an interpreted, high-level and general-purpose programming language. Created by Guido van Rossum and first released in 1991." }, { "name": "JS", "description": "JS is a programming language that conforms to the ECMAScript specification. JavaScript is high-level, often just-in-time compiled, and multi-paradigm." } ]

Running this code results in:

Language{name='Java', description='Java is a class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible.'} Language{name='Python', description='Python is an interpreted, high-level and general-purpose programming language. Created by Guido van Rossum and first released in 1991.'} Language{name='JS', description='JS is a programming language that conforms to the ECMAScript specification. JavaScript is high-level, often just-in-time compiled, and multi-paradigm.'}

Conclusion

In this article, we've used Jackson to parse and map the values from a JSON String and file into a Java array and list.

This is done via the readValue[] method, by specifying the JSON contents [String or file] and by specifying the POJO we'd like to map to.

private List map_string;

Json you need to pass:-

{ "map_formula" : [ { "A+" : "if[price