Frequently Asked questions in JSON framework in Java Class Library
Frequently Asked questions in JSON framework in Java Class Library
JSON (JavaScript Object Notation) is a lightweight data exchange format, which is widely used in front -end data transmission and storage.The Java class library provides many JSON frameworks, such as Jackson, GSON, etc., to process and operate JSON data.This article will answer the common questions of the JSON framework in the Java library and give the corresponding Java code example.
Question 1: How to convert the Java object to a json format string?
It is very simple to convert the Java object to the JSON string with the JSON framework.The following is an example of the Jackson framework:
import com.fasterxml.jackson.databind.ObjectMapper;
public class Main {
public static void main(String[] args) throws Exception {
// Create a Java object
Person person = new Person("John", 25);
// Create ObjectMapper objects
ObjectMapper objectMapper = new ObjectMapper();
// Convert java objects to json string
String jsonString = objectMapper.writeValueAsString(person);
// Print json string
System.out.println(jsonString);
}
}
class Person {
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
// getters and setters
}
Run the above code, the output result is:
{"name":"John","age":25}
Question 2: How to convert JSON strings into Java objects?
Similarly, it is also very simple to convert the JSON string to the Java object with the JSON framework.The following example uses the Jackson framework to analyze:
import com.fasterxml.jackson.databind.ObjectMapper;
public class Main {
public static void main(String[] args) throws Exception {
// json string
String jsonString = "{\"name\":\"John\",\"age\":25}";
// Create ObjectMapper objects
ObjectMapper objectMapper = new ObjectMapper();
// Convert json string to Java object
Person person = objectMapper.readValue(jsonString, Person.class);
// Use Java object
System.out.println("Name: " + person.getName());
System.out.println("Age: " + person.getAge());
}
}
class Person {
private String name;
private int age;
// getters and setters
}
Run the above code, the output result is:
Name: John
Age: 25
Question 3: How to deal with nested objects or arrays in JSON?
In JSON, data can be organized by object nested and array.The JSON framework provides corresponding methods to handle these situations.The following is an example:
import com.fasterxml.jackson.databind.ObjectMapper;
public class Main {
public static void main(String[] args) throws Exception {
// json string
String jsonString = "{\"name\":\"John\",\"age\":25,\"addresses\":[{\"street\":\"Street 1\",\"city\":\"City 1\"},{\"street\":\"Street 2\",\"city\":\"City 2\"}]}";
// Create ObjectMapper objects
ObjectMapper objectMapper = new ObjectMapper();
// Convert json string to Java object
Person person = objectMapper.readValue(jsonString, Person.class);
// Use Java object
System.out.println("Name: " + person.getName());
System.out.println("Age: " + person.getAge());
for (Address address : person.getAddresses()) {
System.out.println("Address: " + address.getStreet() + ", " + address.getCity());
}
}
}
class Person {
private String name;
private int age;
private Address[] addresses;
// getters and setters
}
class Address {
private String street;
private String city;
// getters and setters
}
Run the above code, the output result is:
Name: John
Age: 25
Address: Street 1, City 1
Address: Street 2, City 2
Through the above examples, we can see that the JSON framework can easily handle the condition of nested objects or array.
Question 4: How to deal with the date format in JSON?
The JSON format does not have the type of native support date, but it can be treated with the date of the date of serialization and deepertine.The following examples use the Jackson framework to handle the date format:
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.annotation.JsonDeserialize;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import java.text.SimpleDateFormat;
import java.util.Date;
public class Main {
public static void main(String[] args) throws Exception {
// json string
String jsonString = "{\"name\":\"John\",\"birthDate\":\"2022-01-01\"}";
// Create ObjectMapper objects
ObjectMapper objectMapper = new ObjectMapper();
// Register Date Formatter
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
objectMapper.setDateFormat(dateFormat);
// Convert json string to Java object
Person person = objectMapper.readValue(jsonString, Person.class);
// Use Java object
System.out.println("Name: " + person.getName());
System.out.println("Birth Date: " + person.getBirthDate());
}
}
class Person {
private String name;
@JsonDeserialize(using = CustomDateDeserializer.class)
@JsonSerialize(using = CustomDateSerializer.class)
private Date birthDate;
// getters and setters
}
class CustomDateDeserializer extends JsonDeserializer<Date> {
private SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
@Override
public Date deserialize(JsonParser jsonParser, DeserializationContext context) throws IOException {
String dateStr = jsonParser.getText();
try {
return dateFormat.parse(dateStr);
} catch (ParseException e) {
throw new RuntimeException(e);
}
}
}
class CustomDateSerializer extends JsonSerializer<Date> {
private SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
@Override
public void serialize(Date date, JsonGenerator jsonGenerator, SerializerProvider provider) throws IOException {
String dateString = dateFormat.format(date);
jsonGenerator.writeString(dateString);
}
}
Run the above code, the output result is:
Name: John
Birth Date: Sat Jan 01 00:00:00 CST 2022
By customized dates formators, the format of the date can be specified when serialization and dependentization.
The above is the answer and example of the common questions of the JSON framework in the Java library.According to the specific needs and the characteristics of the JSON framework, these methods can be used to process JSON data flexibly.
