How to put java data into a json file?

Question

I'm doing a school project (create a bus network), and they ask me to put the data (number of the bus and so on) into a json file.

Do you guys have a simple example for me please ? I'm using eclipse, and I tried to use the org.json.simple.JSONObject; library but it does not work.

Cordially

There are many libraries to convert a java object into Json. Probably the most widely used are Jackson and Gson. After you get a Json object then you can write it to a file. Please share the code you are trying so we can help you. — Ezequiel, Jun 28 '19 at 10:51

score 0 · Answer 1 · answered Jun 28 '19 at 10:51

Jackson is the de-facto standard library for reading and writing JSON with Java. It can also be used to read/write XML, YAML and other formats.

There are many tutorials on the web on how to use Jackson, such as http://www.studytrails.com/java/json/jackson-create-json/

General usage:

Create/confiure a ObjectMapper
Create your data beans, and optionally annotate them with Jackson annotations to fine-tune the serialization
Serialize/deserialize your beans using the object mapper.

Sophisticated example which also shows how to serialize from/to other formats, and how to use custom serialization: https://github.com/pwalser75/json-xml-yaml-test

score 0 · Answer 2 · answered Jun 28 '19 at 10:54

0

You can have a look at Java – Write to File and How do I create a file and write to it in Java?

With a POJO:

public class Data {

    private final String name;
    private final String id;

    public Data(final String name, final String id) {
        this.name = name;
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public String getId() {
        return id;
    }
}

And this code using Jackson and ObjectMapper:

ObjectMapper objectMapper = new ObjectMapper();
Data data = new Data("abc", "123");
String jsonData = objectMapper.writeValueAsString(data);
Path path = Paths.get("myFile");
Files.write(path, jsonData.getBytes(StandardCharsets.UTF_8));

answered Jun 28 '19 at 10:54

Thibaud Ledent

1,446
1
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Thanks. If my data is inside an ArrayList, how can I put all that inside this json file ? For example, I've inside an ArrayList all the bus stop, in another one the bus inside the network and so on. – Balaure Jun 28 '19 at 11:04
You can create an object with the two lists: "Data myData = new Data(list1, list2);" or use the lists directly: "System.out.println(objectMapper.writeValueAsString(myList);" – Thibaud Ledent Jun 28 '19 at 11:14
Which import I need to be able to use this code ? Since it does not propose me an import :/ – Balaure Jun 28 '19 at 11:35
`import com.fasterxml.jackson.databind.ObjectMapper;` which can be imported with the [jackson-databind Maven dependency](https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind/2.9.9) – Thibaud Ledent Jun 28 '19 at 12:51
I'm not using maven, since the project is well advanced. it says when I put it "create class ObjectMapper in package com.faster...." :/ – Balaure Jun 28 '19 at 13:02
I finally success to have those import. But I can not find the one for Data, it says it does not exist.. – Balaure Jun 28 '19 at 15:34
You have to create the class `Data` defined above – Thibaud Ledent Jun 30 '19 at 16:41

score 0 · Answer 3 · answered Jun 28 '19 at 11:13

0

If you refer to the example posted here you can see how to handle lists: How to construct JSON data in Java

You can also just put an ArrayList as value instead an array of Strings. Jackson will do the rest for you.

answered Jun 28 '19 at 11:13

arnonuem

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6
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I need to create 2 new class ? I first thought that I just need to put some lines into my files – Balaure Jun 28 '19 at 11:48
You dont need to create model classes if you use generic HashMaps which i already posted here: https://stackoverflow.com/questions/56805274/how-to-construct-json-data-in-java – arnonuem Jun 28 '19 at 11:52
well, it does not recognize "ObjectMapper", which import I need to use ? – Balaure Jun 28 '19 at 11:56
yes you have to download or import it. If you use maven you gould just put a ``` com.fasterxml.jackson.core jackson-databind 2.9.8 ``` Take care to take the latest dependency you can look it up at https://search.maven.org/ – arnonuem Jun 28 '19 at 12:03
I'm not using maven :/ – Balaure Jun 28 '19 at 12:04
than grap the binary from somewhere - you really should use maven nowadays. You need to find com.fasterxml.jackson.core module which contains databinding. – arnonuem Jun 28 '19 at 12:06
well thanks, I don't know how to do it then, i'll try to find something – Balaure Jun 28 '19 at 12:12

score 0 · Answer 4 · edited Jul 02 '19 at 05:33

Here is a file1.txt content:

{
"Name": "crunchify.com",
"Author": "App Shah",
"Company List": [
    "Compnay: eBay",
    "Compnay: Paypal",
    "Compnay: Google"
]
}

Java Code:

    package com.crunchify.tutorials;

    import java.io.FileWriter;
    import java.io.IOException;

    import org.json.simple.JSONArray;
    import org.json.simple.JSONObject;



    public class CrunchifyJSONFileWrite {

    @SuppressWarnings("unchecked")
    public static void main(String[] args) throws IOException {

        JSONObject obj = new JSONObject();
        obj.put("Name", "crunchify.com");
        obj.put("Author", "App Shah");

        JSONArray company = new JSONArray();
        company.add("Compnay: eBay");
        company.add("Compnay: Paypal");
        company.add("Compnay: Google");
        obj.put("Company List", company);

        // try-with-resources statement based on post comment below :)
        try (FileWriter file = new FileWriter("/Users/<username>/Documents/file1.txt")) {
            file.write(obj.toJSONString());
            System.out.println("Successfully Copied JSON Object to File...");
            System.out.println("\nJSON Object: " + obj);
        }
    }
}

How to put java data into a json file?

4 Answers4