Java Gson类型适配器与自定义反序列化程序
下面的示例显示了包含抽象类(成员)集合的类(俱乐部)。我不清楚是否需要TypeAdapter或JsonDeserializer来正确地进行反序列化。序列化可以在没有任何帮助的情况下正常工作,但反序列化会引发异常。为了说明这一点,我构建了以下“克隆”测试。如果有人能拿出一个有效的例子,我将不胜感激 头等舱Java Gson类型适配器与自定义反序列化程序,java,gson,Java,Gson,下面的示例显示了包含抽象类(成员)集合的类(俱乐部)。我不清楚是否需要TypeAdapter或JsonDeserializer来正确地进行反序列化。序列化可以在没有任何帮助的情况下正常工作,但反序列化会引发异常。为了说明这一点,我构建了以下“克隆”测试。如果有人能拿出一个有效的例子,我将不胜感激 头等舱 package gson.test; import java.util.ArrayList; import com.google.gson.Gson; public class Club {
package gson.test;
import java.util.ArrayList;
import com.google.gson.Gson;
public class Club {
public static void main(String[] args) {
// Setup a Club with 2 members
Club myClub = new Club();
myClub.addMember(new Silver());
myClub.addMember(new Gold());
// Serialize to JSON
Gson gson = new Gson();
String myJsonClub = gson.toJson(myClub);
System.out.println(myJsonClub);
// De-Serialize to Club
Club myNewClub = gson.fromJson(myJsonClub, Club.class);
System.out.println(myClub.equals(myNewClub) ? "Cloned!" : "Failed");
}
private String title = "MyClub";
private ArrayList<Member> members = new ArrayList<Member>();
public boolean equals(Club that) {
if (!this.title.equals(that.title)) return false;
for (int i=0; i<this.members.size(); i++) {
if (! this.getMember(i).equals(that.getMember(i))) return false;
}
return true;
}
public void addMember(Member newMember) { members.add(newMember); }
public Member getMember(int i) { return members.get(i); }
}
以及构件的两个具体子类(黄金和白银)
最后是输出
{"title":"MyClub","members":[{"silverData":"SomeSilverData","type":1,"name":""},{"goldData":"SomeGoldData","type":2,"name":""}]}
Exception in thread "main" java.lang.RuntimeException: Failed to invoke public gson.test.Member() with no args
at com.google.gson.internal.ConstructorConstructor$3.construct(ConstructorConstructor.java:107)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:186)
...
Cloned!
{
"title": "MyClub",
"members": [
{
"silverData": "SomeSilverData",
"clsname": "gson.test.Silver",
"type": 1,
"name": "Jack"
},
{
"goldData": "SomeGoldData",
"extraData": "Extra Gold Data",
"clsname": "gson.test.Gold",
"type": 2,
"name": "Jill"
},
{
"silverData": "SomeSilverData",
"clsname": "gson.test.Silver",
"type": 1,
"name": "Mike"
}
]
}
你两者都可以。选择哪一种取决于潜在的性能影响,以及愿意编写多少代码 反序列化程序更昂贵。这是因为反序列化程序的输入是一个json树,GSon必须创建与您的类匹配的属性的完整JsonElement子树,然后才能将其传递给反序列化程序。如果您的类有很多嵌套,那么成本会增加。对于普通对象,它可以忽略不计 似乎您将知道基于将包含在目标对象中的
type
属性的值创建哪个类。您的反序列化程序需要
- 查看传递的
对象,读取JsonElement
属性,确定类型type
- 使用类和传递给您的相同元素调用
context.deserialize()
- 如果类型丢失或无效,则引发错误
类型
属性(您无法预测其位置),然后完成其余属性的读取,并根据类型创建最终的黄金
/白银
对象,读取并保存所有属性。好的,真正的工作示例(这次我非常确定)
俱乐部
package gson.test;
import java.util.ArrayList;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
public class Club {
public static void main(String[] args) {
// Setup a Club with 2 members
Club myClub = new Club();
myClub.addMember(new Silver("Jack"));
myClub.addMember(new Gold("Jill"));
myClub.addMember(new Silver("Mike"));
// Get the GSON Object and register Type Adapter
GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(Member.class, new MemberDeserializer());
builder.registerTypeAdapter(Member.class, new MemberSerializer());
builder.setPrettyPrinting();
Gson gson = builder.create();
// Serialize Club to JSON
String myJsonClub = gson.toJson(myClub);
// De-Serialize to Club
Club myNewClub = gson.fromJson(myJsonClub, Club.class);
System.out.println(myClub.equals(myNewClub) ? "Cloned!" : "Failed");
System.out.println(gson.toJson(myNewClub));
}
private String title = "MyClub";
private ArrayList<Member> members = new ArrayList<Member>();
public boolean equals(Object club) {
Club that = (Club) club;
if (!this.title.equals(that.title)) return false;
for (int i=0; i<this.members.size(); i++) {
Member member1 = this.getMember(i);
Member member2 = that.getMember(i);
if (! member1.equals(member2)) return false;
}
return true;
}
public void addMember(Member newMember) { members.add(newMember); }
public Member getMember(int i) { return members.get(i); }
}
具体的子类银和金
package gson.test;
public class Silver extends Member {
private String silverData = "SomeSilverData";
public Silver() {
super();
this.setType(1);
}
public Silver(String theName) {
super(theName);
this.setType(1);
}
public boolean equals(Object that) {
Silver silver = (Silver)that;
return (super.equals(that) && this.silverData.equals(silver.silverData));
}
}
package gson.test;
public class Gold extends Member {
private String goldData = "SomeGoldData";
private String extraData = "Extra Gold Data";
public Gold() {
super();
this.setType(2);
}
public Gold(String theName) {
super(theName);
this.setType(2);
}
public boolean equals(Gold that) {
Gold gold = (Gold) that;
return (super.equals(that) && this.goldData.equals(gold.goldData));
}
}
自定义成员Serailizer
package gson.test;
import java.lang.reflect.Type;
import com.google.gson.JsonElement;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
public class MemberSerializer implements JsonSerializer<Member> {
public JsonElement serialize(Member src, Type member, JsonSerializationContext context) {
switch (src.getType()) {
case 1: return context.serialize((Silver)src);
case 2: return context.serialize((Gold)src);
default: return null;
}
}
}
我应该注意到,我真正的用例是性能不应该成为问题的,我正在从jSon文本文件加载对象缓存,因此执行此代码的频率使得性能远不如可维护性重要 序列化/反序列化类层次结构似乎是一个常见问题 在官方源repo的
extras
目录中甚至有一个“官方”解决方案(不幸的是,它不是Maven包的一部分)
请检查:
- 解释如下:
- 解决方案:。建议只复制/粘贴源文件
Object
参数类型,而不是Club
谢谢,我会花一点时间来理解。明白了,谢谢,我下次会投票。我匆忙通过测试,我的序列化没有像我想象的那样工作,因此,看起来我还需要一个特殊的序列化程序来深入研究集合的子类型。当我有一个工作示例时,我将继续测试并发布最后一个工作示例。
package gson.test;
public class Silver extends Member {
private String silverData = "SomeSilverData";
public Silver() {
super();
this.setType(1);
}
public Silver(String theName) {
super(theName);
this.setType(1);
}
public boolean equals(Object that) {
Silver silver = (Silver)that;
return (super.equals(that) && this.silverData.equals(silver.silverData));
}
}
package gson.test;
public class Gold extends Member {
private String goldData = "SomeGoldData";
private String extraData = "Extra Gold Data";
public Gold() {
super();
this.setType(2);
}
public Gold(String theName) {
super(theName);
this.setType(2);
}
public boolean equals(Gold that) {
Gold gold = (Gold) that;
return (super.equals(that) && this.goldData.equals(gold.goldData));
}
}
package gson.test;
import java.lang.reflect.Type;
import com.google.gson.JsonElement;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
public class MemberSerializer implements JsonSerializer<Member> {
public JsonElement serialize(Member src, Type member, JsonSerializationContext context) {
switch (src.getType()) {
case 1: return context.serialize((Silver)src);
case 2: return context.serialize((Gold)src);
default: return null;
}
}
}
package gson.test;
import java.lang.reflect.Type;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
public class MemberDeserializer implements JsonDeserializer<Member> {
@Override
public Member deserialize(JsonElement json, Type member, JsonDeserializationContext context) {
int myType = json.getAsJsonObject().get("type").getAsInt();
switch (myType) {
case 1: return context.deserialize(json, Silver.class);
case 2: return context.deserialize(json, Gold.class);
default: return null;
}
}
}
Cloned!
{
"title": "MyClub",
"members": [
{
"silverData": "SomeSilverData",
"clsname": "gson.test.Silver",
"type": 1,
"name": "Jack"
},
{
"goldData": "SomeGoldData",
"extraData": "Extra Gold Data",
"clsname": "gson.test.Gold",
"type": 2,
"name": "Jill"
},
{
"silverData": "SomeSilverData",
"clsname": "gson.test.Silver",
"type": 1,
"name": "Mike"
}
]
}