If I pass a JSON like
`{
"entity":{
"name":"xyz",
"age":21
}
}`
Then , is it compulsory that my POJO should have both "name" and "age" instance variables. I mean, if I have only "name" instance field, will there be any exception while mapping?
If your JSON contains extra fields which are not present in POJO, it will throw an exception. To avoid that you can ignore additional fields using this annotation #JsonIgnoreProperties.
if field names are different, you can define at field getter using #jsonProperty. (for deserialization).
for serialization use annotation on the setter method.
#JsonIgnoreProperties(ignoreUnknown = true)
class Pojo {
private String name;
#jsonProperty("firstName")
public String getName(){
return this.name;
}
}
is it compulsory that my POJO should have both "name" and "age" instance variables
If you mean "have" as in the same names exactly, then no. You can use annotations to rename the values.
If you instead mean the class definition "contains" those values, then also it shouldn't need them. That depends on how you configure ObjectMapper, though. For example, there is an AnyGetter annotation that will allow you to collect "extra" JSON values. Therefore, it makes sense that mandatory fields are not required.
Related
I am looking for an annotation I can use to replace String value to null in Java
There are some #Json annotation that can do customization while serializing a JSON object to POJO,
I want to do something like this:
#JsonFormat(<if incoming value is SOMESTRING>, <set incoming value to null>)
String valueChangedUsingAnnotation;
Use #JsonIgnore annotation. This annotation is used when you want to ignore certain properties of a java class. It will ignore those fields annotated with when reading from json to java object and also, writing java object to json.
If incoming value is SOMETHING, set its value to null. For this you can update the setter method of that particular field in POJO class. Because, when incoming object is deserialized it invokes setter methods of each fields.
Something like below:
class Test{
//constructor, other fields and their getters and setters
private String target;
public void setTarget(String target) {
if(target.equals("abcd"){
this.target=null
}
else {
this.target=target;
}
}
}
There is no need of any JSON annotations.
In my current project the names of the model class fields are German. The fields are all annotated with #JsonProperty for the English translation of the names. E.g. #JsonProperty(value = "operation"). Is there a way in the configuration that the mapping of the fields is done using the JsonProperty annotation?
Example:
public class Auftrag {
#JsonProperty(value = "orderType")
private String auftragsart;
...
}
public class OrderDto {
private String orderType;
}
MapStruct uses the Java Bean convention to detect the properties. This means that it looks in the getters and setters.
Out-of-the-box you cannot use the #JsonProperty. However, you can create your own AccessorNamingStrategy that will provide the properties based on #JsonProperty. The AccessorNamingStrategy gives you access to the Abstract syntax tree, which means you can look for fields in types, check their annotations and check their values.
Keep in mind that MapStruct will only ask to get the property for a method, so you would need to get the property name, then find the field in the type, then look for the #JsonProperty annotation and its value.
You can read more about the AccessorNamingStrategy here in the documentation.
I have a large nested object. I want to serialise this object in the JSON string, however I need only certain fields to be included. Problem here is that fields could change very frequently and I want to build it in a way that could help me easy include or exclude fields for serialisation.
I know that I can write a lot of code to extract certain fields and build JSON "manually". But I wonder if there are any other elegant way to achieve similar outcome but specifying a list of required fields?
For example having following object structure I want include only id and name in the response:
class Building {
private List<Flat> flats;
}
class Flat {
private Integer id;
private Person owner;
}
class Person {
private String name;
private String surname;
}
Json:
{
"flats" : [
{
"flat":
{
"id" : "1",
"person" : {
"name" : "John"
}
}
}
]
}
You can use gson for serializing/deserializing JSON.
Then you can include the #Expose annotation to use only the fields you require.
Be sure to also configure your Gson object to only serialize "exposed" fields.
Gson gson = GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();
Alternative:
You can actually do it the inverse way, marking fields which will not be exposed. You can do this with the transient keyword.
So whatever you want to ignore just add transient to it. Here's how it works on gson.
PS: This works on most Java JSON serializers too.
Using com.fasterxml.jackson.annotation.JsonIgnore is another way to achieve this.
import com.fasterxml.jackson.annotation.JsonIgnore;
class Person {
private String name;
#JsonIgnore
private String surname;
}
It will ignore the surname when the parser converts the bean to json.
Similar annotation will be available in other json processing libraries.
If using Gson, study how to use ExclusionStrategy & JsonSerializer.
Using those is a more flexible way to control serialization since it allows to decide per serialization what to serialize.
Using annotations requires later to add / remove those annotations from fields if there is a need to change what to serialize.
In the case of your example the latter might be more appropriate.
This question might be good startpoint
serialize-java-object-with-gson
Does naybody knows a way to use Jersey's GET method to return a JSON that returns only some fields of an entity instead of all?
Does anybody know a way to use Jersey's GET method to return a JSON that returns only some fields of an entity instead of all?
E.g. in the following class I want to receive (with POST) values for 'name' and for 'confidential', buy while returning (with GET) I only need 'name' value, not 'confidential'.
#Entity
#Table(name = "a")
#XmlRootElement
#JsonIgnoreProperties({"confifentialInfo"})
public class A extends B implements Serializable {
private String name;
#Basic(optional = false)
private String confifentialInfo;
// more fields, getters and setters
}
If you are using the JAXB approach, you can mark fields with #XmlTransient to omit them. If you are using POJO mapping or want to exclude fields only for some requests, you should construct the JSON with the low level JSON API.
If you are using Jackson, you can use the annotation #JsonIgnore for methods
Marker annotation similar to javax.xml.bind.annotation.XmlTransient
that indicates that the annotated method is to be ignored by
introspection-based serialization and deserialization functionality.
That is, it should not be consider a "getter", "setter" or "creator".
And #JsonIgnoreProperties for properties
Annotation that can be used to either suppress serialization of
properties (during serialization), or ignore processing of JSON
properties read (during deserialization).
I'm using MappingJacksonJsonView to serialize to JSON a class, however, I'd like to be able to rename some of the fields from the default name based on the getter name.
This is because I've to output field names like "delete_url" and "delete_type" for jQuery file upload. I'm using #Jsonserialize annotation to hand pick the fields to serialize.
#JsonAutoDetect(getterVisibility = Visibility.NONE)
public interface Picture {
#JsonSerialize
String getName();
#JsonSerialize
String getDelete_url();
...
For instance, I'm forced to call a method getDelete_url(), while I'd like to call it getDeleteUrl(), but still output the key "delete_url" when serializing to JSON.
You should be able to qualify using #JsonProperty.
#JsonAutoDetect(getterVisibility = Visibility.NONE)
public interface Picture {
#JsonSerialize
#JsonProperty("name")
String getName();
#JsonSerialize
#JsonProperty("delete_url")
String getDeleteUrl();
//...
Have you tried using the #JsonProperty annotation?
"Defines name of the logical property, i.e. Json object field name to use for the property: if empty String (which is the default), will use name of the field that is annotated."