I would like to generate a JSON String from my object:
Gson gson = new Gson();
String json = gson.toJson(item);
Everytime I try to do this, I get this error:
14:46:40,236 ERROR [[BomItemToJSON]] Servlet.service() for servlet BomItemToJSON threw exception
java.lang.StackOverflowError
at com.google.gson.stream.JsonWriter.string(JsonWriter.java:473)
at com.google.gson.stream.JsonWriter.writeDeferredName(JsonWriter.java:347)
at com.google.gson.stream.JsonWriter.value(JsonWriter.java:440)
at com.google.gson.internal.bind.TypeAdapters$7.write(TypeAdapters.java:235)
at com.google.gson.internal.bind.TypeAdapters$7.write(TypeAdapters.java:220)
at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.write(ReflectiveTypeAdapterFactory.java:89)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.write(ReflectiveTypeAdapterFactory.java:200)
at com.google.gson.internal.bind.TypeAdapterRuntimeTypeWrapper.write(TypeAdapterRuntimeTypeWrapper.java:68)
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:96)
at com.google.gson.internal.bind.CollectionTypeAdapterFactory$Adapter.write(CollectionTypeAdapterFactory.java:60)
at com.google.gson.Gson$FutureTypeAdapter.write(Gson.java:843)
These are the attributes of my BomItem class:
private int itemId;
private Collection<BomModule> modules;
private boolean deprecated;
private String partNumber;
private String description; //LOB
private int quantity;
private String unitPriceDollar;
private String unitPriceEuro;
private String discount;
private String totalDollar;
private String totalEuro;
private String itemClass;
private String itemType;
private String vendor;
private Calendar listPriceDate;
private String unitWeight;
private String unitAveragePower;
private String unitMaxHeatDissipation;
private String unitRackSpace;
Attributes of my referenced BomModule class:
private int moduleId;
private String moduleName;
private boolean isRootModule;
private Collection<BomModule> parentModules;
private Collection<BomModule> subModules;
private Collection<BomItem> items;
private int quantity;
Any idea what causes this error? How can I fix it?
That problem is that you have a circular reference.
In the BomModule
class you are referencing to:
private Collection<BomModule> parentModules;
private Collection<BomModule> subModules;
That self reference to BomModule
, obviously, not liked by GSON at all.
A workaround is just set the modules to null
to avoid the recursive looping. This way I can avoid the StackOverFlow-Exception.
item.setModules(null);
Or mark the fields you don't want to show up in the serialized json by using the transient
keyword, eg:
private transient Collection<BomModule> parentModules;
private transient Collection<BomModule> subModules;