How to prevent Gson serialize / deserialize the first character of a field (underscore)? - json

Question

My class:
class ExampleBean {
private String _firstField;
private String _secondField;
// respective getters and setters
}
I want to appear as follows:
{
"FirstField":"value",
"SecondField":"value"
}
And not like this
{
"_FirstField":"value",
"_SecondField":"value"
}
I initialize the parser as follows:
GsonBuilder builder = new GsonBuilder();
builder.setDateFormat(DateFormat.LONG);
builder.setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE);
builder.setPrettyPrinting();
set_defaultParser(builder.create());
I could see the API and in the documentation of "FieldNamePolicy" but I am surprised that not give the option to skip "_"
I also know I can use the annotation...
# SerializedName (" custom_naming ")
...but do not want to have to write this for alllllll my fields ...
It's very useful for me to distinguish between local variables and fields of a class. :( Any Idea?
EDIT: There would be many obvious solutions, (inheritance, gson overwriting methods, regular expresions). My question is more focused on whether there is a native solution of gson or a less intrusive fix?
Maybe we could propose as new FieldNamePolicy?

Answer 1

GsonBuilder provides a method setFieldNamingStrategy() that allows you to pass your own FieldNamingStrategy implementation.
Note that this replaces the call to setFieldNamingPolicy() - if you look at the source for GsonBuilder these two methods are mutually exclusive as they set the same internal field (The FieldNamingPolicy enum is a FieldNamingStrategy).
public class App
{
public static void main(String[] args)
{
Gson gson = new GsonBuilder()
.setFieldNamingStrategy(new MyFieldNamingStrategy())
.setPrettyPrinting()
.create();
System.out.println(gson.toJson(new ExampleBean()));
}
}
class ExampleBean
{
private String _firstField = "first field value";
private String _secondField = "second field value";
// respective getters and setters
}
class MyFieldNamingStrategy implements FieldNamingStrategy
{
public String translateName(Field field)
{
String fieldName =
FieldNamingPolicy.UPPER_CAMEL_CASE.translateName(field);
if (fieldName.startsWith("_"))
{
fieldName = fieldName.substring(1);
}
return fieldName;
}
}
Output:
{
"FirstField": "first field value",
"SecondField": "second field value"
}

Answer 2

What you want is
import java.lang.reflect.Field;
import java.text.DateFormat;
import com.google.gson.FieldNamingStrategy;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
public class GsonExample {
public static void main(String... args) throws Exception {
final GsonBuilder builder = new GsonBuilder();
builder.setDateFormat(DateFormat.LONG);
builder.setPrettyPrinting();
builder.setFieldNamingStrategy(new FieldNamingStrategy() {
#Override
public String translateName(Field f) {
String fieldName = f.getName();
if(fieldName.startsWith("_") && fieldName.length() > 1) {
fieldName = fieldName.substring(1, 2).toUpperCase() + fieldName.substring(2);
}
return fieldName;
}
});
final Gson gson = builder.create();
System.out.println(gson.toJson(new ExampleBean("example", "bean")));
}
private static class ExampleBean {
private final String _firstField;
private final String _secondField;
private ExampleBean(String _firstField, String _secondField) {
this._firstField = _firstField;
this._secondField = _secondField;
}
}
}
which generates
{"FirstField":"example","SecondField":"bean"}