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https://github.com/johncarl81/parceler

:package: Android Parcelables made easy through code generation.
https://github.com/johncarl81/parceler

android android-parcelable annotation-processor boilerplate java

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:package: Android Parcelables made easy through code generation.

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= Parceler



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Have a question?  http://stackoverflow.com/questions/ask?tags=parceler[Ask it on StackOverflow.]



Found an issue?  https://github.com/johncarl81/parceler/issues/new[Please report it.]



In Android, http://developer.android.com/reference/android/os/Parcelable.html[Parcelables] are a great way to serialize Java Objects between Contexts.

http://www.developerphil.com/parcelable-vs-serializable/[Compared] with traditional Serialization, Parcelables take on the order of 10x less time to both serialize and deserialize.

There is a major flaw with Parcelables, however.

Parcelables contain a ton of boilerplate code.

To implement a Parcelable, you must mirror the `writeToParcel()` and `createFromParcel()` methods such that they read and write to the Parcel in the same order.

Also, a Parcelable must define a `public static final Parcelable.Creator CREATOR` in order for the Android infrastructure to be able to leverage the serialization code.



Parceler is a code generation library that generates the Android Parcelable boilerplate source code.

No longer do you have to implement the Parcelable interface, the `writeToParcel()` or `createFromParcel()` or the `public static final CREATOR`.

You simply annotate a POJO with `@Parcel` and Parceler does the rest.

Because Parceler uses the Java JSR-269 Annotation Processor, there is no need to run a tool manually to generate the Parcelable code.

Just annotate your Java Bean, compile and you are finished.

By default, Parceler will serialize the fields of your instance directly:



[source,java]

----

@Parcel

public class Example {

    String name;

    int age;



    public Example() {}



    public Example(int age, String name) {

        this.age = age;

        this.name = name;

    }



    public String getName() { return name; }



    public int getAge() { return age; }

}

----



Be careful not to use private fields when using the default field serialization strategy as it will incur a performance penalty due to reflection.



To use the generated code, you may reference the generated class directly, or via the `Parcels` utility class:



[source,java]

----

Parcelable wrapped = Parcels.wrap(new Example("Andy", 42));

----



To dereference the `@Parcel`, just call the `Parcels.unwrap()` method:



[source,java]

----

Example example = Parcels.unwrap(wrapped);

example.getName(); // Andy

example.getAge(); // 42

----



Of course, the wrapped `Parcelable` can be added to an Android Bundle to transfer from Activity to Activity:



[source,java]

----

Bundle bundle = new Bundle();

bundle.putParcelable("example", Parcels.wrap(example));

----



And dereferenced in the `onCreate()` method:



[source,java]

----

Example example = Parcels.unwrap(getIntent().getParcelableExtra("example"));

----



This wrapping and unwrapping technique plays well with the Intent Factory pattern.

In addition, Parceler is supported by the following libraries:



 * http://androidtransfuse.org/documentation.html#parcel[Transfuse] - Allows `@Parcel` annotated beans to be used with the `@Extra` injection.

 * https://github.com/sockeqwe/fragmentargs#argsbundler[FragmentArgs] - Uses the `ParcelerArgsBundler` adapter to wrap and unwrap `@Parcel` annotated beans with fragment parameters.

 * https://github.com/f2prateek/dart[Dart] - Autodetects `@Parcel` annotated beans and automatically unwraps them when using `@InjectExtra`.

 * http://androidannotations.org/[AndroidAnnotations] - Autodetects `@Parcel` annotated beans and https://github.com/excilys/androidannotations/wiki/ParcelerIntegration[automatically wraps/unwraps] them when using `@Extra`, `@FragmentArg`, `@InstanceState` and other `Bundle` related annotations.

 * https://github.com/MarcinMoskala/ActivityStarter/wiki/Parceler-Arg-Converter-usage[ActivityStarter] - Supports natively Parceler objects as arguments to Activities, Fragments, Services, etc.

 * https://josesamuel.com/remoter/[Remoter] - Supports natively Parceler objects as arguments in @Remoter interfaces. 



=== Parcel attribute types

Only a select number of types may be used as attributes of a `@Parcel` class.

The following list includes the mapped types:



 * `byte`

 * `double`

 * `float`

 * `int`

 * `long`

 * `char`

 * `boolean`

 * `String`

 * `IBinder`

 * `Bundle`

 * `SparseArray` of any of the mapped types*

 * `SparseBooleanArray`

 * `ObservableField`

 * `List`, `ArrayList` and `LinkedList` of any of the mapped types*

 * `Map`, `HashMap`, `LinkedHashMap`, `SortedMap`, and `TreeMap` of any of the mapped types*

 * `Set`, `HashSet`, `SortedSet`, `TreeSet`, `LinkedHashSet` of any of the mapped types*

 * `Parcelable`

 * `Serializable`

 * Array of any of the mapped types

 * Any other class annotated with `@Parcel`



*Parcel will error if the generic parameter is not mapped.



Parceler also supports any of the above types directly.

This is especially useful when dealing with collections of classes annotated with `@Parcel`:



[source,java]

----

Parcelable listParcelable = Parcels.wrap(new ArrayList());

Parcelable mapParcelable = Parcels.wrap(new HashMap());

----



==== Polymorphism

Note that Parceler does not unwrap inheritance hierarchies, so any polymorphic fields will be unwrapped as instances of the base class.

This is because Parceler opts for performance rather than checking `.getClass()` for every piece of data.



[source,java]

----

@Parcel

public class Example {

    public Parent p;

    @ParcelConstructor Example(Parent p) { this.p = p; }

}



@Parcel public class Parent {}

@Parcel public class Child extends Parent {}

----



[source,java]

----

Example example = new Example(new Child());

System.out.println("%b", example.p instanceof Child); // true

example = Parcels.unwrap(Parcels.wrap(example));

System.out.println("%b", example.p instanceof Child); // false

----



Refer to the <> section for an example of working with polymorphic fields.



=== Serialization techniques



Parceler offers several choices for how to serialize and deserialize an object in addition to the field-based serialization seen above.



==== Getter/setter serialization

Parceler may be configured to serialize using getter and setter methods and a non-empty constructor.

In addition, fields, methods and constructor parameters may be associated using the `@ParcelProperty` annotation.

This supports a number of bean strategies including immutability and traditional getter/setter beans.



To configure default method serialization, simply configure the `@Parcel` annotation with `Serialization.BEAN`:



[source,java]

----

@Parcel(Serialization.BEAN)

public class Example {

    private String name;

    private int age;

    private boolean enabled;



    public String getName() { return name; }

    public void setName(String name) { this.name = name; }



    public int getAge() { return age; }

    public void setAge(int age) { this.age = age; }

    

    public boolean isEnabled() { return enabled; }

    public void setEnabled(boolean enabled) { this.enabled = enabled; }

}

----



To use a constructor with serialization, annotate the desired constructor with the `@ParcelConstructor` annotation:



[source,java]

----

@Parcel(Serialization.BEAN)

public class Example {

    private final String name;

    private final int age;

    private boolean enabled;



    @ParcelConstructor

    public Example(int age, String name, boolean enabled) {

        this.age = age;

        this.name = name;

        this.enabled = enabled;

    }



    public String getName() { return name; }



    public int getAge() { return age; }

    

    public boolean isEnabled() { return enabled; }

}

----



If an empty constructor is present, Parceler will use that constructor unless another constructor is annotated.



==== Mixing getters/setters and fields

You may also mix and match serialization techniques using the `@ParcelProperty` annotation.

In the following example, `firstName` and `lastName` are written to the bean using the constructor while `firstName` is read from the bean using the field and `lastName` is read using the `getLastName()` method.

The parameters `firstName` and `lastName` are coordinated by the parameter names `"first"` and `"last"` respectfully.



[source,java]

----

@Parcel

public class Example {

    @ParcelProperty("first")

    String firstName;

    String lastName;



    @ParcelConstructor

    public Example(@ParcelProperty("first") String firstName, @ParcelProperty("last") String lastName){

        this.firstName = firstName;

        this.lastName = lastName;

    }



    public String getFirstName() { return firstName; }



    @ParcelProperty("last")

    public String getLastName() { return lastName; }

}

----



For attributes that should not be serialized with Parceler, the attribute field, getter or setter may be annotated by `@Transient`.



Parceler supports many different styles centering around the POJO.

This allows `@Parcel` annotated classes to be used with other POJO based libraries, including the following:



 * https://code.google.com/p/google-gson/[GSON]

 * https://realm.io/docs/java/latest/#parceler[Realm]

 * https://bitbucket.org/littlerobots/cupboard[Cupboard]

 * http://simple.sourceforge.net/[Simple XML]

 * https://github.com/Raizlabs/DBFlow[DBFlow]



==== Static Factory support

As an alternative to using a constructor directly, Parceler supports using an annotated Static Factory to build an instance of the given class.

This style supports Google's https://github.com/google/auto/tree/master/value[AutoValue] annotation processor / code generation library for generating immutable beans.

Parceler interfaces with AutoValue via the `@ParcelFactory` annotation, which maps a static factory method into the annotated `@Parcel` serialization:



[source,java]

----

@AutoValue

@Parcel

public abstract class AutoValueParcel {



    @ParcelProperty("value") public abstract String value();



    @ParcelFactory

    public static AutoValueParcel create(String value) {

        return new AutoValue_AutoValueParcel(value);

    }

}

----



AutoValue generates a different class than the annotated `@Parcel`, therefore, you need to specify which class Parceler should build in the `Parcels` utility class:



[source,java]

----

Parcelable wrappedAutoValue = Parcels.wrap(AutoValueParcel.class, AutoValueParcel.create("example"));

----

And to deserialize:

[source,java]

----

AutoValueParcel autoValueParcel = Parcels.unwrap(wrappedAutoValue);

----



==== Custom serialization

`@Parcel` includes an optional parameter to include a manual serializer `ParcelConverter` for the case where special serialization is necessary.

This provides a still cleaner option for using Parcelable classes than implementing them by hand.



The following code demonstrates using a `ParcelConverter` to unwrap the inheritance hierarchy during deserialization.



[source,java]

----

@Parcel

public class Item {

    @ParcelPropertyConverter(ItemListParcelConverter.class)

    public List itemList;

}

@Parcel public class SubItem1 extends Item {}

@Parcel public class SubItem2 extends Item {}



public class ItemListParcelConverter implements ParcelConverter> {

    @Override

    public void toParcel(List input, Parcel parcel) {

        if (input == null) {

            parcel.writeInt(-1);

        }

        else {

            parcel.writeInt(input.size());

            for (Item item : input) {

                parcel.writeParcelable(Parcels.wrap(item), 0);

            }

        }

    }



    @Override

    public List fromParcel(Parcel parcel) {

        int size = parcel.readInt();

        if (size < 0) return null;

        List items = new ArrayList();

        for (int i = 0; i < size; ++i) {

            items.add((Item) Parcels.unwrap(parcel.readParcelable(Item.class.getClassLoader())));

        }

        return items;

    }

}

----



Parceler is also packaged with a series of base classes to make Collection conversion easier located under the `org.parceler.converter` package of the api.

These base classes take care of a variety of difficult or verbose jobs dealing with Collections including null checks and collectin iteration.

For instance, the above `ParcelConverter` could be written using the `ArrayListParcelConverter':



[source,java]

----

public class ItemListParcelConverter extends ArrayListParcelConverter {

    @Override

    public void itemToParcel(Item item, Parcel parcel) {

        parcel.writeParcelable(Parcels.wrap(item), 0);

    }



    @Override

    public Item itemFromParcel(Parcel parcel) {

        return Parcels.unwrap(parcel.readParcelable(Item.class.getClassLoader()));

    }

}

----



=== Classes without Java source

For classes whose corresponding Java source is not available, one may include the class as a Parcel by using the `@ParcelClass` annotation.

This annotation may be declared anywhere in the compiled source that is convenient.

For instance, one could include the `@ParcelClass` along with the Android Application:



[source,java]

----

@ParcelClass(LibraryParcel.class)

public class AndroidApplication extends Application{

    //...

}

----



Multiple `@ParcelClass` annotations may be declared using the `@ParcelClasses` annotation.



In addition, classes referenced by `@ParcelClass` may be configured using the `@Parcel` annotation.

This allows the serialization configuration through any parameter available on the `@Parcel` annotation including the serialization technique or classes to analyze.



One useful technique is the ability to define global custom converters for a type:

[source,java]

----

@ParcelClass(

    value = LibraryParcel.class,

    annotation = @Parcel(converter = LibraryParcelConverter.class))

class SomeClass{}

----

This allows for fine grained control over a class that isn't available for direct modification.



=== Advanced configuration



==== Skipping analysis

It is a common practice for some libraries to require a bean to extend a base class.

Although it is not the most optimal case, Parceler supports this practice by allowing the configuration of what classes in the inheritance hierarchy to analyze via the analyze parameter:



[source, java]

----

@Parcel(analyze = {One.class, Three.class})

class One extends Two {}

class Two extends Three {}

class Three extends BaseClass {}

----



In this example, only fields of the `One` and `Three` classes will be serialized, avoiding both the `BaseClass` and `Two` class parameters.



==== Specific wrapping



The Parcels utility class looks up the given class for wrapping by class.

For performance reasons this ignores inheritance, both super and base classes.

There are two solutions to this problem.

First, one may specify additional types to associate to the given type via the `implementations` parameter:



[source, java]

----

class ExampleProxy extends Example {}

@Parcel(implementations = {ExampleProxy.class})

class Example {}



ExampleProxy proxy = new ExampleProxy();

Parcels.wrap(proxy);  // ExampleProxy will be serialized as a Example

----



Second, one may also specify the class type when using the `Parcels.wrap()` method:



[source, java]

----

ExampleProxy proxy = new ExampleProxy();

Parcels.wrap(Example.class, proxy);

----



==== Configuring Proguard



To configure Proguard, add the following lines to your proguard configuration file.  These will keep files related to the `Parcels` utilty class and the `Parcelable` `CREATOR` instance:

er

----

# Parceler library

-keep interface org.parceler.Parcel

-keep @org.parceler.Parcel class * { *; }

-keep class **$$Parcelable { *; }

----



== Getting Parceler



You may download Parceler as a Maven dependency:



[source,xml]

----



    org.parceler

    parceler

    1.1.12

    provided



    org.parceler

    parceler-api

    1.1.12



----



or Gradle:

[source,groovy]

----

implementation 'org.parceler:parceler-api:1.1.12'

annotationProcessor 'org.parceler:parceler:1.1.12'

----



Or from http://search.maven.org/#search%7Cga%7C1%7Cg%3A%22org.parceler%22[Maven Central].



== License

----

Copyright 2011-2015 John Ericksen



Licensed under the Apache License, Version 2.0 (the "License");

you may not use this file except in compliance with the License.

You may obtain a copy of the License at



   http://www.apache.org/licenses/LICENSE-2.0



Unless required by applicable law or agreed to in writing, software

distributed under the License is distributed on an "AS IS" BASIS,

WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

See the License for the specific language governing permissions and

limitations under the License.

----