I went through the Consuming a RESTful Web Service guide on the Spring website, but it doesn't talk about how to deserialize nested objects. For example, how would I deserialize the location entry in the sample?
You have to create a domain object for the Location data that is a reference in the top-level Page object. Below is an overly simplified look at the classes. You'll need to properly annotate the objects to serialize/deserialize how you want it to and there are numerous examples on how to do that depending on what markup framework you use.
public class Page {
String id;
String about;
...
Location location;
...
}
public class Location {
String street;
String city;
...
}
Related
I have come across a problem of parsing json data . I am building project using spring boot based on REST api . When i have to parse data corresponding to domain then it is very easy , i use RequestBody in controller method with domain name but in current scenerio i have a list of domain in json form :
{
"data":[
{
"type":"abc",
"subtypes":[
{
"leftValue":"BEACH",
"rightValue":"MOUNTAIN",
"preferencePoint":60
},
{
"leftValue":"ADVENTURE",
"rightValue":"LEISURE",
"preferencePoint":60
}
]
},
{
"type":"mno",
"subtypes":[
{
"leftValue":"LUXURY",
"rightValue":"FUNCTIONAL",
"preferencePoint":60
},
{
"leftValue":"SENSIBLE",
"rightValue":"AGGRESIVE",
"preferencePoint":0
}
]
}
]
}
I am sending data in list where type is the property of class Type
and class Type has list of Subtypes class and subtype class contains leftValue and rightValue as enums
I am using spring boot which uses jackson liberary by default and i want to parse this data into corresponding Type class using Jackson. Can any one provide me solution.
It wasn't clear to me if you have static or dynamic payload.
Static payload
For static one, I would personally try to simplify your payload structure. But your structure would look like this. (I skipped getters and setters. You can generate them via Lombok library).
public class Subtype{
private String leftValue;
private String rightValue;
private int preferencePoint;
}
public class Type{
private String type;
private List<Subtype> subtypes;
}
public class Data{
private List<Type> data;
}
Then in your controller you inject Data type as #RequestBody.
Dynamic payload
For dynamic payload, there is option to inject LinkedHashMap<String, Object> as #RequestBody. Where value in that map is of type Object, which can be casted into another LinkedHashMap<String, Object> and therefore this approach support also nested objects. This can support infinite nesting this way. The only downside is that you need to cast Objects into correct types based on key from the map.
BTW, with pure Spring or Spring Boot I was always able to avoid explicit call against Jackson API, therefore I don't recommend to go down that path.
I need to validate a JSON list similar to the following:
[{"op":"A","path":"C","value":"B"},...]
in a Spring MVC application - I am currently deserializing (using default Jackson) to an object along the lines of:
public class Operations extends ArrayList<Operation>{}
public class Operation {
#NotEmpty
public String op;
#NotEmpty
public String path;
public Object value;
public void setOp(String op)... and other getters/setters
}
but I cannot figure out how to get jsr303 validation provided by reference hibernate implementation to fire for the attributes of Operation.
I can get it to function if I wrap the list in a class but then I have an incorrect format for the JSON, ie something like:
{"ops":[{"op":"A",...},...]}
is it possible to validate the first object (Operations)? and if not is it possible to serialize the first format (ie the JSON list) to an object of the second format (ie a list wrapped in a placeholder object with a placeholder field)
Update
Having failed to find a way to trigger the jsr303 validation on a bare ArrayList I have written a custom jackson json deserializer to stick it into a containing object with an annotated field along the lines of
#JsonDeserialize(using=OperationsDeserializer.class)
public class Operations {
#NotEmpty
private ArrayList<Operation> ops;
public void setOps(ArrayList<Operation>ops)...
public ArrayList<Operation> getOps()...
}
This works but now any autogenerated documentation for my api is generating json examples with the dummy "ops" field in it - ie {"ops" : [ ... ] }
so the search for a method of triggering jsr303 validation on an ArrayList that is not a field of another object continues - perhaps there is a way to inject a proxy wrapping class at runtime that might work around this?
Use ObjectMapper.class. it has a method which will convert Json Object into Class Object
method is , new ObjectMapper().readValue(String str, Class<T> valueType)
So you can iterate your Object array, convert to string and pass it to this method to get your result.
so it would look like,
new ObjectMapper().readValue(object.toString, Operation.class);
I am currently prototyping replacing the GWT-RPC based backend of our application to a REST based API using RestyGWT on the frontend and Spring MVC on the backend.
My issue occurs during the Java <-> JSON type conversions that both frameworks attempt to resolve automatically. All of our data objects use private fields, and many of the fields do not provide java bean style setter methods. By default, neither framework would inspect the private fields of a class and so this conversion fails.
For Spring MVC it was simple enough to fix this by adding an annotation to the data objects:
#JsonAutoDetect(fieldVisibility = Visibility.ANY, getterVisibility = Visibility.NONE, setterVisibility = Visibility.NONE)
For RestyGWT I have not found a suitable fix. The only available workaround I have found is to use default access to all fields and constructors which is far from ideal. Does anybody have a solution that will allow RestyGWT to inspect the private fields of a Java object?
Try using #JsonProperty and #JsonCreator (do not remeber if both are necessary) on your fields.
public abstract class Parent
{
#JsonCreator
public Parent(#JsonProperty("name") String name)
{
this.name = name;
}
public String getName()
{
return name;
}
private String name;
}
Question regarding combination of Jackson/JPA
If there are about 20 entities in current application and I have add Jackson dependency in POM, does it mean all entities are by default ready to convert to JSON object? I saw a sample project seems only class annotated as #JsonIgnored is skipped by JSON. If so, then how can this happen, what is behind such mechanism? how JACKSON handle those entities which don't have any Jackson annotation, by default ignored or not? I've been looking for resources online but not much luck.
If only one of the 20 entities need to be mapped to JSON object, does it mean I have to add #JsonIgnore to all other 19 entities? If not, how Jackson differentiate with entity to work on?
Thanks.
Jackson and JPA don't have anything to do with each other. Jackson is a JSON parsing library and JPA is a persistence framework. Jackson can serialize almost any object - the only requirement being that the object have some kind of recognizable properties (Javabean type properties, or bare fields annotated with #JsonProperty. There is an additional requirement for deserialization, that the target type have a default (no-arg) constructor. So, for example, this is an object that Jackson can serialize:
// Class with a single Javabean property, "name"
class Person {
private String name;
public String getName() { return name ; }
public String setName(String name) { this.name = name ; }
}
And here is another:
// Class with a single field annotated with #JsonProperty
class Account {
#JsonProperty("accountNumber")
private String accountNumber;
}
And here is yet another:
#Entity
public class User {
#Id
private Long id;
#Basic
private String userName;
#Basic
#JsonIgnore
private String password;
#Basic
#JsonIgnore
private Address address;
// Constructors, getters, setters
}
The last example shows a JPA entity class - as far as Jackson is concerned it can be serialized just like any other type. But, take note of its fields: when this object is serialized into JSON two of the fields will not be included - 'password' and 'address'. This is because they have been annotated with #JsonIgnore. The #JsonIgnore annotation allows a developer to say 'Hey, its ok to serialize this object, but when you do so don't include these fields in the output'. This exclusion only occurs for the fields of this object, so for example, if you included an Address field in another class, but did not mark the field as ignorable, it would be serialized.
To prevent serialization of a type in all cases, regardless of context, use the #JsonIgnoreType annotation. When used on a type it basically means 'I dont care where this type is used, never serialize it'.
No, you don't need to add #JsonIgnore on every class and if you had tried you would have gotten a compile error, since you can't put it there. Jackson will only work on objects you give to it, it's no magic.
The Jackson documentation is easily found online, such at its project page on github or on the codehaus website.
My question is, whether it is necessary to add #XmlElement before each element in your pojo to be picked up by jaxb, when making a JSON response. I am using jersey-json 1.17 . The reason I ask this is because, the example given on Jersey site does not use the annotation.
I get an out put as {}, but when I add #XmlElement before the attributes, I get the expected JSON output. Am I doing something wrong, because of which my JSON string is empty ?
My code :
The vertices list is populated in the constructor.
This produces the wrong output of {}
#XmlRootElement
public class SquareModel {
List<Float> vertices = new ArrayList<Float>();
....
}
Whereas this produces the a correct JSON string :
#XmlRootElement
public class SquareModel {
#XmlElement(name="vertices")
List<Float> vertices = new ArrayList<Float>();
....
}
My resource class which returns the JSON
#GET
#Produces(MediaType.APPLICATION_JSON)
public SquareModel getJsonString() {
return new SquareModel();
}
Thanks :)
No, by default a JAXB (JSR-22#) implementation will treat all public fields and properties (get/set combinations) as mapped (not requiring the #XmlElement annotation).
http://blog.bdoughan.com/2012/07/jaxb-no-annotations-required.html
If you wish to annotate a field I would recommend annotating your class with #XmlAccessorType(XmlAccessType.FIELD)
http://blog.bdoughan.com/2011/06/using-jaxbs-xmlaccessortype-to.html
According to this http://jersey.java.net/nonav/documentation/latest/json.html#json.jaxb.approach.section
You should have this annotation (I'm also using it in my code, even though it XML oriented, but it gives me cool JSON also)
Taking this approach will save you a lot of time, if you want to
easily produce/consume both JSON and XML data format. Because even
then you will still be able to use a unified Java model. Another
advantage is simplicity of working with such a model, as JAXB
leverages annotated POJOs and these could be handled as simple Java
beans.
A disadvantage of JAXB based approach could be if you need to work
with a very specific JSON format. Then it could be difficult to find a
proper way to get such a format produced and consumed. This is a
reason why a lot of configuration options are provided, so that you
can control how things get serialized out and deserialized back.
Following is a very simple example of how a JAXB bean could look like.
Example 5.3. Simple JAXB bean implementation
#XmlRootElement
public class MyJaxbBean {
public String name;
public int age;
public MyJaxbBean() {} // JAXB needs this
public MyJaxbBean(String name, int age) {
this.name = name;
this.age = age;
}
}