将 Object 转换为 JSON 文件，然后转换为字节以保存到存储，然后返回到 Object

Question

Suppose I have the class Student which only has name and age attributes.

public class Student {
     private String studentName;
     private Integer age;
}

I want to convert this Student objects to JSON files (I think I can do this with Jackson mapper)

Then I need to store this.json file to an storage, so I have the method save(String key, byte[] resource) which saves any kind of file to the storage (.zip, .txt, etc.).

So I was wondering if I can do this like so:

1. Write value as String with jackson (Student to json)
2. Get the bytes of this String
3. Save to the Storage with save(studentName, bytes)

Back to Student object:

Then when I search an student from the storage I would need to convert back to String like so:

Charset charset = Charset.forName("UTF-8");
String string = new String(studentBytes, charset);

Then String back to Student with Jackson mapper

Is this a good approach (I think not because the idea is that those bytes are actually a.json file, but are bytes of a java String object)? I am a little confused because the "file bytes" that I am saving are from a String object with this approach, but I can not find how to convert the Student object to a ".json file", can not figure out how to save.json file (which I do not need to save in disk because I only need the bytes to save to the cloud storage), how would I write an Object to an "in memory.json file" or maybe is not to see it as a file, just as bytes right? Please point in the right direction, like how to directly write the object to a json file and then store this file bytes?

Answer 1

Yes this is how you want to do it if you want to save json to a file to upload to S3. Jackson has a native json data structure (I think it's called JsonNode ) but you don't want to save that to a file. Just save the json string to a text file.

To convert Student object to String:

Student student = new Student("Joe", 25);
ObjectMapper mapper = new ObjectMapper();
String json_string = mapper.writeValueAsString(student);

You can save this string to a text file and upload to S3. When you want to get the Student object back:

ObjectMapper mapper = new ObjectMapper();
Student student = mapper.readValue(new File("student.json"), Student.class);

Note that there is nothing special about a "json file". It's just a text file with the .json extention. It contains text data that happens to be in the Json format. You can save json_string to a file like this:

Path path = Paths.get("student.json");
byte[] strToBytes = json_string.getBytes();
Files.write(path, strToBytes);

(Reference: https://www.baeldung.com/jackson-object-mapper-tutorial )