当尝试序列化原始问题中描述的数据结构时,Gson 确实抱怨循环引用错误。
下面的例子说明了这一点。
import com.google.gson.Gson;
public class GsonFoo
{
public static void main(String[] args)
{
MyBean bean = new MyBean();
bean.data = "some data";
bean.problem = new RuntimeException("Ack!");
System.out.println(new Gson().toJson(bean));
}
}
class MyBean
{
public String data;
public Exception problem;
}
此示例会导致来自 Gson 的以下异常和消息。
Exception in thread "main" java.lang.IllegalStateException: circular reference error
Offending field: cause
Offending object: preserveType: false, type: class java.lang.Throwable, obj: java.lang.RuntimeException: Ack!
at com.google.gson.CircularReferenceException.createDetailedException(CircularReferenceException.java:43)
at com.google.gson.JsonSerializationVisitor.visitObjectField(JsonSerializationVisitor.java:117)
...
当尝试像下面这样简单的事情时,Gson 同样会窒息。
System.out.println(new Gson().toJson(new RuntimeException("Ack!")));
Gson 目前没有可用的配置来简单地解决这个问题。我建议将问题记录在http://code.google.com/p/google-gson/issues/list http://code.google.com/p/google-gson/issues/list.
如果一个对象带有Exception
引用必须序列化,如果必须使用 Gson,则对引用进行自定义序列化处理Exception
必须执行参考。以下是这样一个例子。
import java.lang.reflect.Type;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
public class GsonFoo
{
public static void main(String[] args)
{
MyBean bean = new MyBean();
bean.data = "some data";
bean.problem = new RuntimeException("Ack!");
GsonBuilder gsonBuilder = new GsonBuilder();
gsonBuilder.registerTypeAdapter(Exception.class, new ExceptionSerializer());
Gson gson = gsonBuilder.create();
System.out.println(gson.toJson(bean));
}
}
class ExceptionSerializer implements JsonSerializer<Exception>
{
@Override
public JsonElement serialize(Exception src, Type typeOfSrc, JsonSerializationContext context)
{
JsonObject jsonObject = new JsonObject();
jsonObject.add("cause", new JsonPrimitive(String.valueOf(src.getCause())));
jsonObject.add("message", new JsonPrimitive(src.getMessage()));
return jsonObject;
}
}
class MyBean
{
public String data;
public Exception problem;
}
output:
{"data":"some data","problem":{"cause":"null","message":"Ack!"}}
物有所值,Jackson http://jackson.codehaus.org当尝试序列化相同的数据结构时,不会出现类似的阻塞。杰克逊连载了MyBean
实例转换为 JSON,如下所示。
{
"data":"some data",
"problem":
{
"cause":null,
"message":"Ack!",
"localizedMessage":"Ack!",
"stackTrace":
[
{
"className":"com.stackoverflow.q8151082.JacksonFoo",
"fileName":"JacksonFoo.java",
"lineNumber":11,
"methodName":"main",
"nativeMethod":false
}
]
}
}