GSON Versioning Support with @Since Annotation
GSON introduced the @Since annotation to support multiple versions of the same object. We can use this annotation on Classes and Fields. In order to enable this feature we need to register a version number to use when serializing/deserializing. If no version number is set on the Gson instance, all the fields will be serialized/deserialized regardless of the version. Gson Versioning basically allows you to hide or add fields of your classes to support multiple versions.
Gson Versioning Support
The @Since annotation is used to annotate your classes or fields with a version number. This annotation takes a double as argument indicating the version number from when this field is available.
package com.memorynotfound.json;
import com.google.gson.annotations.Since;
import java.lang.management.ManagementFactory;
@Since(1.0)
public class Health {
@Since(1.1)
private String hostname;
@Since(1.1)
private String ip;
private long startTime;
private long upTime;
public Health(String hostname, String ip) {
this.hostname = hostname;
this.ip = ip;
this.startTime = ManagementFactory.getRuntimeMXBean().getStartTime();
this.upTime = ManagementFactory.getRuntimeMXBean().getUptime();
}
}When no version number is specified in the Gson instance, all fields are serialized/deserialized. When a version number is specified, all fields that match that version number are used.
package com.memorynotfound.json;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
public class Run {
public static void main(String... args){
Health health = new Health("https://memorynotfound.com", "123.123.123.123");
Gson gson = new GsonBuilder()
.setPrettyPrinting()
.create();
String result = gson.toJson(health);
System.out.println("Without version: " + result);
gson = new GsonBuilder()
.setVersion(1.0)
.setPrettyPrinting()
.create();
result = gson.toJson(health);
System.out.println("Version 1.0: " + result);
gson = new GsonBuilder()
.setVersion(1.1)
.setPrettyPrinting()
.create();
result = gson.toJson(health);
System.out.println("Version 1.1: " + result);
}
}Generated output.
Without version: {
"hostname": "https://memorynotfound.com",
"ip": "123.123.123.123",
"startTime": 1455099486512,
"upTime": 52
}
Version 1.0: {
"startTime": 1455099486512,
"upTime": 52
}
Version 1.1: {
"hostname": "https://memorynotfound.com",
"ip": "123.123.123.123",
"startTime": 1455099486512,
"upTime": 52
}