Looking back on JSON handled by Java

Preface

I noticed that I lacked knowledge when dealing with JSON. I would like to summarize to the level that it is possible to handle JSON at least with java if there is only this (The library uses JSONIC)

JSON basics

When dealing with JSON in Java, handle String written in JSON format 　String→POJO POJO → String, etc.

JSON format rules (reading)

① The list structure is enclosed in [] ② The POJO structure is surrounded by {} ③ There is no part that specifies the name of the POJO structure that is the parent I think you can read it as soon as you remember the above three

sample

 {
    "id": 1,
    "name": "shoes",
    "price": 12000,
    "shops": [
      {
         "name": "Astore",
         "location": "tokyo"
      },
      {
         "name": "Bstore",
         "location": "oosaka"
      }
    ]
 }

Sample POJO

	public class Product {
		public Integer id;
		public String name;
		public Integer price;
		public List<Shop> shops;
	}

	public class Shop {
		public String name;
		public String location;
	}

Treatment of Jackson

When using the above JSON and POJO

JSON→Java

		String json = "{\"id\": 1,\"name\": \"shoes\",\"price\": 12000,\"shops\": [{\"name\": \"Astore\",\"location\": \"tokyo\"},{\"name\": \"Bstore\",\"location\": \"oosaka\"}]}";
		ObjectMapper mapper = new ObjectMapper();
		Product data = mapper.readValue(json, Product.class);

When sent in the structure of a list or map

		ObjectMapper mapper = new ObjectMapper();
		List<Product> products = mapper.readValue(json, new TypeReference<List<Product>>() {});

Java→JSON

		ObjectMapper mapper = new ObjectMapper();
		String json = mapper.writeValueAsString(product);

Other

・ POJO will give an error if each property is pullic or does not have Getter / Setter. -An error will occur if there is a property that POJO does not have when converting from JSON to Java. → If you add "@JsonIgnoreProperties (ignoreUnknown = true)" to POJO, no error will occur. → Only necessary data can be extracted