@JsonProperty annotation on field as well as getter/setter

Question

I have inherited a certain bit code that has the @JsonProperty annotation on getter/setters. The purpose is so that when the object is serialized using the Jackson library, the fields have that specific name.

Current code:

private String fileName;

@JsonProperty("FILENAME")
public String getFileName()
{
    return fileName;
}

@JsonProperty("FILENAME")
public void setFileName(String fileName)
{
    this.fileName = fileName;
}

Now for another tool, I need to annotate the field with JsonProperty as well. So this will be my changed code:

@JsonProperty("FILENAME")
private String fileName;

@JsonProperty("FILENAME")
public String getFileName()
{
    return fileName;
}

@JsonProperty("FILENAME")
public void setFileName(String fileName)
{
    this.fileName = fileName;
}

Has anyone used this same annotation on both - the field as well as the getter/setters? I looked around on the net but didn't see anything.

I have compiled & run the code but I'm not sure if this would this cause any problems down the road. Any thoughts on this?

As it is you wouldn't have a problem because you're not doing anything in the setter other than setting the value. However, if that were to change I'd worry about which one Jackson would use; if it picked the field, you might not get the behavior you're expecting. Unfortunately I can't find anything on the order of precedence for you. — Brian Roach
+1. Yes, an order of precedence would be useful, but of course they really should not HAVE different names. — OceanBlue

Biju Kunjummen Biju Kunjummen · Accepted Answer · 2012-07-17T18:45:37

My observations based on a few tests has been that whichever name differs from the property name is one which takes effect:

For eg. consider a slight modification of your case:

@JsonProperty("fileName")
private String fileName;

@JsonProperty("fileName")
public String getFileName()
{
    return fileName;
}

@JsonProperty("fileName1")
public void setFileName(String fileName)
{
    this.fileName = fileName;
}

Both fileName field, and method getFileName, have the correct property name of fileName and setFileName has a different one fileName1, in this case Jackson will look for a fileName1 attribute in json at the point of deserialization and will create a attribute called fileName1 at the point of serialization.

Now, coming to your case, where all the three @JsonProperty differ from the default propertyname of fileName, it would just pick one of them as the attribute(FILENAME), and had any on of the three differed, it would have thrown an exception:

java.lang.IllegalStateException: Conflicting property name definitions

@JsonProperty annotation on field as well as getter/setter

2 Answers