json array to list in java with code examples

JSON (JavaScript Object Notation) is a lightweight data interchange format that is easy to read and write for humans and machines. It is commonly used in web applications, where it can be used to exchange data between the client and server. JSON is particularly useful when working with arrays, since it can represent arrays in a concise and easy-to-read format.

One of the most common tasks when working with JSON is converting JSON arrays to lists in Java. In this article, we will discuss how to achieve this using Java code examples.

Converting JSON Arrays to Lists in Java

Firstly, it is important to note that there are many libraries that can be used for working with JSON data in Java, such as Jackson, GSON, and JSON-lib. For the purposes of this article, we will be using the Jackson library.

To start, we need to create a JSON array. Here is an example of how we can create a JSON array using Jackson:

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.node.ArrayNode;

ObjectMapper mapper = new ObjectMapper();
ArrayNode arrayNode = mapper.createArrayNode();

arrayNode.add("one");
arrayNode.add("two");
arrayNode.add("three");

String jsonArrayString = arrayNode.toString();

In the example above, we used the ObjectMapper class to create a new JSON array. We then added three strings to the array using the add() method. We then converted the array to a JSON string using the toString() method.

Next, we can convert the JSON array to a list using the following Java code:

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

ObjectMapper mapper = new ObjectMapper();
try {
    JsonNode node = mapper.readTree(jsonArrayString);
    List<String> myList = new ArrayList<String>();
    for (JsonNode jsonNode : node) {
        myList.add(jsonNode.asText());
    }
} catch (IOException e) {
    e.printStackTrace();
}

In the example above, we use the ObjectMapper class to read the JSON string and convert it to a JsonNode object. We then create a new empty list using the ArrayList class. We then loop through each item in the JsonNode and use the asText() method to convert each item to a string. Finally, we add each string to the list.

Conclusion

Converting JSON arrays to lists in Java is a common task when working with JSON data. In this article, we have discussed how to achieve this using Java code examples. We have used the Jackson library to create a JSON array and convert it to a list. We have also discussed some of the other libraries that can be used for working with JSON data in Java.

Creating a JSON Array in Java

To create a JSON array in Java, we can use various libraries like Jackson, GSON, and JSON-lib. Here is an example of creating a JSON array using the GSON library:

import com.google.gson.JsonArray;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;

JsonArray jsonArray = new JsonArray();

JsonObject jsonObject1 = new JsonObject();
jsonObject1.addProperty("name", "John");
jsonObject1.addProperty("age", 25);
jsonArray.add(jsonObject1);

JsonObject jsonObject2 = new JsonObject();
jsonObject2.addProperty("name", "Mary");
jsonObject2.addProperty("age", 30);
jsonArray.add(jsonObject2);

String jsonArrayString = jsonArray.toString();

In the example above, we first create a new empty JSON array using the JsonArray class. We then create two new JSON objects using the JsonObject class and add them to the array using the add() method. Finally, we convert the array to a JSON string using the toString() method.

Converting a JSON Array to a List in Java

To convert a JSON array to a list in Java, we can use various libraries like Jackson, GSON, and JSON-lib. Here is an example of converting a JSON array to a list using the GSON library:

import com.google.gson.Gson;
import com.google.gson.JsonArray;
import com.google.gson.JsonObject;
import com.google.gson.reflect.TypeToken;

TypeToken<List<JsonObject>> token = new TypeToken<List<JsonObject>>(){};
List<JsonObject> myList = new Gson().fromJson(jsonArrayString, token.getType());

In the example above, we create a new TypeToken object to represent our desired list type. We then use the Gson library to deserialize the JSON string to a List object.

Alternatively, we can use Jackson to convert a JSON array to a list in the following way:

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.JsonNode;

ObjectMapper objectMapper = new ObjectMapper();
JsonNode jsonNode = objectMapper.readTree(jsonArrayString);

List<JsonNode> myList = new ArrayList<>();
jsonNode.forEach(myList::add);

In the example above, we used ObjectMapper to parse the JSON string to a JsonNode. We then created an empty ArrayList of JsonNode and looped over the nodes of the JsonNode using forEach method and added each node to the List.

Conclusion

JSON arrays are commonly used in web applications for exchanging data between the client and server. In Java, we have various libraries available like Jackson, GSON, and JSON-lib, to create and work with JSON arrays. We can easily convert JSON arrays to lists using these libraries.

Popular questions

  1. What is a JSON array in Java?
  • A JSON array is a data structure that holds a collection of values in a JSON format.
  1. Why would we need to convert a JSON array to a list in Java?
  • Sometimes we might need to work with the contents of a JSON array in Java code. Converting a JSON array to a list can make this easier by allowing us to access the elements of the array as standard Java objects.
  1. What libraries can be used for working with JSON data in Java?
  • There are several libraries that can be used for working with JSON data in Java, such as Jackson, GSON, and JSON-lib. These libraries provide classes and methods for creating, parsing, and manipulating JSON data.
  1. How can we create a JSON array in Java using Jackson?
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.node.ArrayNode;

ObjectMapper mapper = new ObjectMapper();
ArrayNode arrayNode = mapper.createArrayNode();

arrayNode.add("one");
arrayNode.add("two");
arrayNode.add("three");

String jsonArrayString = arrayNode.toString();
  1. How can we convert a JSON array to a list in Java using GSON?
import com.google.gson.Gson;
import com.google.gson.JsonArray;
import com.google.gson.JsonObject;
import com.google.gson.reflect.TypeToken;

TypeToken<List<JsonObject>> token = new TypeToken<List<JsonObject>>(){};
List<JsonObject> myList = new Gson().fromJson(jsonArrayString, token.getType());

Tag

"JSON-to-List"

As a senior DevOps Engineer, I possess extensive experience in cloud-native technologies. With my knowledge of the latest DevOps tools and technologies, I can assist your organization in growing and thriving. I am passionate about learning about modern technologies on a daily basis. My area of expertise includes, but is not limited to, Linux, Solaris, and Windows Servers, as well as Docker, K8s (AKS), Jenkins, Azure DevOps, AWS, Azure, Git, GitHub, Terraform, Ansible, Prometheus, Grafana, and Bash.

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