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{#==========================================
Spincast Jackson Json plugin
==========================================#}
{% extends "../../layout.html" %}
{% block sectionClasses %}plugins plugins-spincast-jackson-json{% endblock %}
{% block meta_title %}Plugins - Spincast Jackson Json{% endblock %}
{% block meta_description %}Spincast Jackson Json plugin provides Json functionalities using Jackson.{% endblock %}
{% block scripts %}
{% endblock %}
{% block body %}
Plugins- Spincast Jackson Json plugin
Overview
The Spincast Jackson Json plugin provides Json functionalities
using Jackson. It contains an implementation
of the IJsonManager interface.
Most of the time, the IJsonManager interface is used directly from
the request context via the
json() method or indirectly via
some methods on the response() add-on.
For example:
{% verbatim %}
public class AppController {
public void myHandler(IDefaultRequestContext context) {
// Create a Json object, using the "json()" add-on
IJsonObject jsonObj = context.json().create();
// Send an object as Json, using the "response()" add-on
context.response().sendJsonObj(jsonObj);
}
}{% endverbatim %}
You can also directly inject the IJsonManager
instance where you need it in your application.
Installation
If you use the spincast-default artifact, this plugin is already installed so
you have nothing more to do!
If you start from scratch using the spincast-core artifact, you can use the
plugin by adding this artifact to your project:
<dependency>
<groupId>org.spincast</groupId>
<artifactId>spincast-plugins-jackson-json</artifactId>
<version>{{spincastCurrrentVersion}}</version>
</dependency>
You then install the plugin's Guice module, by passing it to the Guice.createInjector(...) method:
Injector guice = Guice.createInjector(
new SpincastCoreGuiceModule(args),
new SpincastJacksonJsonPluginGuiceModule(IAppRequestContext.class,
IAppWebsocketContext.class)
// other modules...
);
... or by using the install(...) method from your custom Guice module:
public class AppModule extends SpincastCoreGuiceModule {
@Override
protected void configure() {
super.configure();
install(new SpincastJacksonJsonPluginGuiceModule(getRequestContextType(),
getWebsocketContextType()));
// other modules...
}
// ...
}
The IJsonManager interface
Methods :
-
IJsonObject create()
Creates an empty JsonObject
-
IJsonObject create(String jsonString)
Creates a JsonObject from a Json
String.
-
IJsonObject create(InputStream inputStream)
Creates a JsonObject from an inputStream.
-
IJsonArray createArray()
Creates an empty JsonArray.
-
IJsonArray createArray(String jsonString)
Creates a JsonArray from a Json
String.
-
IJsonArray createArray(InputStream inputStream)
Creates a JsonArray from an inputStream.
-
String toJsonString(Object obj)
Gets the Json String representation of
the specified object.
-
String toJsonString(Object obj, boolean pretty)
Gets the Json String representation of the
specified object.
-
Map<String, Object> fromJsonStringToMap(String jsonString)
Creates a Map<String, Object> from a Json
String.
-
Map<String, Object> fromJsonInputStreamToMap(InputStream inputStream)
Creates a Map<String, Object> from a Json inputStream.
-
<T> T fromJsonString(String jsonString, Class<T> clazz)
Creates an instance of the specified T type
from a Json String.
-
<T> T fromJsonInputStream(InputStream inputStream, Class<T> clazz)
Creates an instance of the specified T type
from a Json inputStream.
-
Date parseDateFromJson(String str)
Converts a Json date to a Java UTC date.
Main configurations
You can bind a ISpincastJsonManagerConfig implementation to tweak
the default configurations
used by the components this plugin provides. By default, the
SpincastJsonManagerConfigDefault class is used as the implementation.
-
int getPrettyPrinterIndentationSpaceNumber()
The number of spaces to used to indent generated Json when
pretty print is used.
Defaults to 4 spaces.
-
String getPrettyPrinterNewlineChars()
The newline character(s) to use for generated Json when
pretty print is used.
Defaults to \n, wathever the platform the application is running on.
(de)serialization configurations
Jackson allows some configuration when serializing and deserializing an object.
Most of those configurations
are defined using annotations.
You can annotate the objects directly, or you can use mix-ins.
Annotating the objects :
If you don't minds annotating your objects with Jackson specific annotations,
this is maybe the simplest thing to do. For example, let's say you have a User
class that has two fields, name and title, and you don't want
to keep the title field when you
serialize an instance of this class:
public class User implements IUser {
private String name;
private String title;
@Override
public String getName() {
return this.name;
}
@Override
public void setName(String name) {
this.name = name;
}
@Override
public String getTitle() {
return this.title;
}
@Override
public void setTitle(String title) {
this.title = title;
}
}
To ignore the title field to be included during the serialization, you can simply
annotate the getTitle() method with
@JsonIgnore:
public class User implements IUser {
private String name;
private String title;
@Override
public String getName() {
return this.name;
}
@Override
public void setName(String name) {
this.name = name;
}
@Override
@JsonIgnore
public String getTitle() {
return this.title;
}
@Override
public void setTitle(String title) {
this.title = title;
}
}
If you serialize an instance of this class using the Json Manager,
only the name property would be kept:
IUser user = new User();
user.setName("Stromgol");
user.setTitle("alien");
String jsonString = getJsonManager().toJsonString(user);
assertEquals("{\"name\":\"Stromgol\"}", jsonString);
Using mix-ins:
Many developers (us included) don't like to pollute their model classes
with too many annotations. Lucky us, Jackson provides a way to configure
objects from the outside, without annotating the objects directly, by using what is called
mix-ins annotations.
Let's start with the same User class, without any Jackson annotations:
public class User implements IUser {
private String name;
private String title;
@Override
public String getName() {
return this.name;
}
@Override
public void setName(String name) {
this.name = name;
}
@Override
public String getTitle() {
return this.title;
}
@Override
public void setTitle(String title) {
this.title = title;
}
}
To use Json mix-ins in a Spincast application,
you first need to create the mix-in abstract class. Interfaces work too, but
only to annotate methods, not fields.
An example mix-in for our IUser objects:
public abstract class IUserMixin implements IUser {
// Ignore this property!
@Override
@JsonIgnore
public abstract String getTitle();
}
As you can see, a mix-in extends the class/interface to configure, and adds
the Jackson annotations on the overriding fields or methods declarations.
Once the mix-in is defined, you have to register it, in your custom
Guice module:
public class AppModule extends SpincastDefaultGuiceModule {
public AppModule(String[] mainArgs) {
super(mainArgs);
}
@Override
protected void configure() {
super.configure();
bindJsonMixins();
//...
}
protected void bindJsonMixins() {
Multibinder<IJsonMixinInfo> jsonMixinsBinder = Multibinder.newSetBinder(binder(), IJsonMixinInfo.class);
jsonMixinsBinder.addBinding().toInstance(new JsonMixinInfo(IUser.class, IUserMixin.class));
}
}
Explanation :
-
18 : A
multibinder is used
to collect the various mix-ins to register. The advantage of a multibinder
is that it allows to register mix-ins from any Guice module. For example, some
plugins may want to register their mix-ins, and you may want to register your custom ones.
-
19 : We register our mix-in, by binding a
JsonMixinInfo instance, which specifies the class to configure, and the
class of the mix-in used to configure it.
With this in place, Spincast will automatically configure Jackson so it uses your mix-ins, and
you would have the exact same result than annotating the User
class directly:
IUser user = new User();
user.setName("Stromgol");
user.setTitle("alien");
String jsonString = getJsonManager().toJsonString(user);
assertEquals("{\"name\":\"Stromgol\"}", jsonString);
{% endblock %}
Spincast Jackson Json 
Spincast Jackson Json