从Java对象到JSON对象的自定义转换 [英] Custom Conversion from Java Object to JSON Object

问题描述

我有以下代码：

  Gson gson = new Gson（）; 
 String json = gson.toJson（criteria.list（））; // list由Hibernate传递
  

结果如下所示：

  {creationTime：0，enabled：true，id：1，loginDuration：0，online：false，userName：someone} 
  

我想在JSON响应中添加新的属性（DT_RowId，它与id具有相同的值）。最终结果应该如下所示：

  {creationTime：0，enabled：true，id：1，loginDuration：0，online ：false，userName：someone，DT_RowId = 1} 
  

$ b UPDATED

为了解决这个问题，我在实体上创建了一个包含@Transient注解的字段。

  ... 
 @Transient 
私人长DT_RowId; 
 
 public void setId（long id）{
 this.id = id; 
 this.DT_RowId = id; 
} 
 ... 
  

然而，setId函数从未被调用过。有人能给我启发吗？

解决方案

GSON不会调用你的getters和setters。它通过反射直接访问成员变量。要完成您正在尝试的操作，您需要使用GSON自定义串行器/解串器。 GSON在定制串行器/解串器上的文档提供一些例子来说明如何做到这一点。

下面是一个使用JUnit测试的实例，演示了如何实现它：

Entity.java

  public class实体{
 protected long creationTime; 
保护布尔启用; 
保护长ID; 
保护长loginDuration; 
保护布尔线上; 
保护字符串userName; 
保护长DT_RowId; 
 
 
 
 $ b 
 EntityJsonSerializer.java 
 
 
 
  import java.lang.reflect.Type; 
 import com.google.gson。*; 
 
 public class EntityJsonSerializer实现了JsonSerializer< Entity> {
 @Override 
 public JsonElement serialize（Entity entity，Type typeOfSrc，JsonSerializationContext context）{
 entity.DT_RowId = entity.id; 
 Gson gson = new Gson（）; 
 return gson.toJsonTree（entity）; 
} 
} 
  
 
 
 
 JSONTest.java 
 
 
 
  import static org.junit.Assert。*; 
 import org.junit.Test; 
 import com.google.gson。*; 
 
 public class JSONTest {
 @Test 
 public final void testSerializeWithDTRowId（）{
 Entity entity = new Entity（）; 
 entity.creationTime = 0; 
 entity.enabled = true; 
 entity.id = 1; 
 entity.loginDuration = 0; 
 entity.online = false; 
 entity.userName =someone; 
 
 GsonBuilder builder = new GsonBuilder（）; 
 builder.registerTypeAdapter（Entity.class，new EntityJsonSerializer（））; 
 Gson gson = builder.create（）; 
 String json = gson.toJson（entity）; 
 String expectedJson ={\creationTime \：0，\enabled\：true，\id \：1，\loginDuration \：0，\\ \\ online\：假，\ userName\：\ someone\，\ DT_RowId\：1}; 
 assertEquals（expectedJson，json）; 
} 
} 
  
 
I have the following code
Gson gson = new Gson();
String json = gson.toJson(criteria.list()); // list is passed by Hibernate
The result would be something like this:
{creationTime:0, enabled:true, id:1, loginDuration:0, online:false, userName:someone}
I would like to add new attribute (DT_RowId which has the same value as id) within the JSON response. The end result should be like this:
{creationTime:0, enabled:true, id:1, loginDuration:0, online:false, userName:someone, DT_RowId=1}
UPDATED

I created a field with @Transient annotation on the entity in order to solve this issue.
    ...
    @Transient
    private long DT_RowId;

    public void setId(long id) {
            this.id = id;
            this.DT_RowId=id;
        }
    ...
However the setId function was never been called. Can someone enlighten me on this ?
解决方案
GSON won't call your getters and setters. It accesses member vars directly via reflection. To accomplish what you are trying to do, you will need to use a GSON custom serializer/deserializer. The GSON docs on custom serializers/deserializers provide some examples for how to do this.

Here is a working example with a passing JUnit test that demonstrates how to do it:

Entity.java

public class Entity {
    protected long creationTime;
    protected boolean enabled;
    protected long id;
    protected long loginDuration;
    protected boolean online;
    protected String userName;
    protected long DT_RowId;
}


EntityJsonSerializer.java

import java.lang.reflect.Type;
import com.google.gson.*;

public class EntityJsonSerializer implements JsonSerializer<Entity> {
    @Override
    public JsonElement serialize(Entity entity, Type typeOfSrc, JsonSerializationContext context) {
       entity.DT_RowId = entity.id;
       Gson gson = new Gson();
       return gson.toJsonTree(entity);
    }
}


JSONTest.java

import static org.junit.Assert.*;
import org.junit.Test;
import com.google.gson.*;

public class JSONTest {
    @Test
    public final void testSerializeWithDTRowId() {
        Entity entity = new Entity();
        entity.creationTime = 0;
        entity.enabled = true;
        entity.id = 1;
        entity.loginDuration = 0;
        entity.online = false;
        entity.userName = "someone";

        GsonBuilder builder = new GsonBuilder();
        builder.registerTypeAdapter(Entity.class, new EntityJsonSerializer());
        Gson gson = builder.create();
        String json = gson.toJson(entity);
        String expectedJson = "{\"creationTime\":0,\"enabled\":true,\"id\":1,\"loginDuration\":0,\"online\":false,\"userName\":\"someone\",\"DT_RowId\":1}";
        assertEquals(expectedJson, json);
    }
}


                        
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