EasyGSON: Analysis of JSON annotations and reflection mechanisms in the Java class library
EasyGSON: Analysis of JSON annotations and reflection mechanisms in the Java class library
Introduction:
With the rapid development of the Internet, the demand for data exchange is increasing.JSON (JavaScript Object Notation), as a lightweight data exchange format, has become a tool often used in Internet development.As a widely used programming language, Java also provides a wealth of libraries to process JSON data.EasyGson is a Java class library that provides a simple and easy way to process JSON data.This article will explore the JSON annotations and reflection mechanisms in the EasyGSon class library.
1. json annotation
The JSON annotation refers to the field name in JSON in the Java class and the type of field in JSON.EasyGson provides several commonly used JSON annotations, including:
1. @SerializeDname: Used to specify the JSON field name corresponding to the field of the Java class.For example:
public class User {
@SerializedName("name")
private String userName;
//...
}
In the above code, the@SerializedName ("name") annotation specifies that the JSON field corresponding to the username field in the Java class is called "name".
2. @Expose: What fields are used to specify which fields need to be serialized and deactivated.For example:
public class User {
@Expose
private String userName;
//...
}
In the above code, the@Expose annotation specifies the username field in the Java class that needs to be serialized and derived.
3. @SINCE and @Atntil: The version range for specified fields.For example:
public class User {
@Since(1.0)
@Until(2.0)
private String userName;
//...
}
In the above code,@SINCE (1.0) and@Attil (2.0) specify the username field in the Java class to be effective between version 1.0 and 2.0.
Second, reflection mechanism
The reflection mechanism refers to the dynamic information of the class when the program is runtime, and can operate the attributes, methods and constructors of the class.Easygson uses the reflection mechanism to analyze the annotations in the Java class, and maximize the annotations and JSON data.The main application of the reflection mechanism in EasyGson includes:
1. Analysis annotation: EasyGson analyzes JSON data by obtaining the fields, methods and class levels in the Java class.By calling the relevant methods in the reflective API, the information in the annotation can be obtained to process the corresponding processing.
2. Serialization and deactivation: EasyGSon can serialize JSON data into Java objects according to the information in the annotation, or sequences of the Java object into JSON data.By calling the relevant methods in the reflective API, the values of the field can be obtained and settled, thereby completing the process of serialization and deepening.
3. Dynamic Creation Object: EasyGSon can dynamically create Java objects through the reflection mechanism.By calling the relevant methods in the reflective API, you can obtain the constructor of the class and call the newInstance () method to create an object.
Java code example:
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;
import com.google.gson.reflect.TypeToken;
import java.lang.reflect.Field;
import java.lang.reflect.Type;
import java.util.HashMap;
import java.util.Map;
public class EasyGsonExample {
public static void main(String[] args) {
// Create GSON objects
Gson gson = new GsonBuilder()
.excludefieldswithoutexposeannotation () // rule
.create();
// Create a Java object
User user = new User();
user.setusername ("Zhang San");
user.setAge(20);
user.setEmail("zhangsan@example.com");
// The object is converted to JSON string
String json = gson.toJson(user);
System.out.println ("JSON string:" + json);
// json string convert to object
User user2 = gson.fromJson(json, User.class);
System.out.println ("Java object:" + user2.getUsername () + "," + user2.getage () + "," + user2.Getemail ());
}
// Define the User class
static class User {
@Expose
@SerializedName("name")
private String userName;
@Expose
private int age;
@Expose
private String email;
// getter and setter method
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
}
}
The above code demonstrates how to use EasyGson's annotations in the Java class, and uses the reflex mechanism for serialization and derivativeization operations.
in conclusion:
Through the introduction of this article, we understand the application of JSON annotations and reflection mechanisms in the EasyGSON class library.The JSON annotation provides a flexible way to process the mapping of JSON data, and the reflection mechanism enables EasyGson to dynamically analyze and operate the comments and fields of the Java class during runtime.With EasyGson, we can easily process JSON data and convert each other with Java objects.
references:
1. EasyGSON official document: https://github.com/google/gson
2. Java reflection mechanism: https://www.runoob.com/java/java- reflection.html
