moshi/README.md

Moshi
=====

Moshi is a modern JSON library for Android and Java. It makes it easy to parse JSON into Java
objects:

```java
String json = ...;

Moshi moshi = new Moshi.Builder().build();
JsonAdapter<BlackjackHand> jsonAdapter = moshi.adapter(BlackjackHand.class);

BlackjackHand blackjackHand = jsonAdapter.fromJson(json);
System.out.println(blackjackHand);
```

And it can just as easily serialize Java objects as JSON:

```java
BlackjackHand blackjackHand = new BlackjackHand(
    new Card('6', SPADES),
    Arrays.asList(new Card('4', CLUBS), new Card('A', HEARTS)));

Moshi moshi = new Moshi.Builder().build();
JsonAdapter<BlackjackHand> jsonAdapter = moshi.adapter(BlackjackHand.class);

String json = jsonAdapter.toJson(blackjackHand);
System.out.println(json);
```

### Built-in Type Adapters

Moshi has built-in support for reading and writing Java’s core data types:

 * Primitives (int, float, char...) and their boxed counterparts (Integer, Float, Character...).
 * Arrays, Collections, Lists, Sets, and Maps
 * Strings
 * Enums

It supports your model classes by writing them out field-by-field. In the example above Moshi uses
these classes:

```java
class BlackjackHand {
  public final Card hidden_card;
  public final List<Card> visible_cards;
  ...
}

class Card {
  public final char rank;
  public final Suit suit;
  ...
}

enum Suit {
  CLUBS, DIAMONDS, HEARTS, SPADES;
}
```

to read and write this JSON:

```
{
  "hidden_card": {
    "rank": "6",
    "suit": "SPADES"
  },
  "visible_cards": [
    {
      "rank": "4",
      "suit": "CLUBS"
    },
    {
      "rank": "A",
      "suit": "HEARTS"
    }
  ]
}
```

The [Javadoc][javadoc] catalogs the complete Moshi API, which we explore below.

### Custom Type Adapters

With Moshi, it’s particularly easy to customize how values are converted to and from JSON. A type
adapter is any class that has methods annotated `@ToJson` and `@FromJson`.

For example, Moshi’s default encoding of a playing card is verbose: the JSON defines the rank and
suit in separate fields: `{"rank":"A","suit":"HEARTS"}`. With a type adapter, we can change the
encoding to something more compact: `"4H"` for the four of hearts or `"JD"` for the jack of
diamonds:

```java
class CardAdapter {
  @ToJson String toJson(Card card) {
    return card.rank + card.suit.name().substring(0, 1);
  }

  @FromJson Card fromJson(String card) {
    if (card.length() != 2) throw new JsonDataException("Unknown card: " + card);

    char rank = card.charAt(0);
    switch (card.charAt(1)) {
      case 'C': return new Card(rank, Suit.CLUBS);
      case 'D': return new Card(rank, Suit.DIAMONDS);
      case 'H': return new Card(rank, Suit.HEARTS);
      case 'S': return new Card(rank, Suit.SPADES);
      default: throw new JsonDataException("unknown suit: " + card);
    }
  }
}
```

Register the type adapter with the `Moshi.Builder` and we’re good to go.

```java
Moshi moshi = new Moshi.Builder()
    .add(new CardAdapter())
    .build();
```

Voila:

```json
{
  "hidden_card": "6S",
  "visible_cards": [
    "4C",
    "AH"
  ]
}
```

### Fails Gracefully

Automatic databinding almost feels like magic. But unlike the black magic that typically accompanies
reflection, Moshi is designed to help you out when things go wrong.

```
JsonDataException: Expected one of [CLUBS, DIAMONDS, HEARTS, SPADES] but was ANCHOR at path $.visible_cards[2].suit
  at com.squareup.moshi.JsonAdapters$11.fromJson(JsonAdapters.java:188)
  at com.squareup.moshi.JsonAdapters$11.fromJson(JsonAdapters.java:180)
	...
```

Moshi always throws a standard `java.io.IOException` if there is an error reading the JSON document,
or if it is malformed. It throws a `JsonDataException` if the JSON document is well-formed, but
doesn’t match the expected format.

### Built on Okio

Moshi uses [Okio][okio] for simple and powerful I/O. It’s a fine complement to [OkHttp][okhttp],
which can share buffer segments for maximum efficiency.

### Borrows from Gson

Moshi uses the same streaming and binding mechanisms as [Gson][gson]. If you’re a Gson user you’ll
find Moshi works similarly. If you try Moshi and don’t love it, you can even migrate to Gson without
much violence!

But the two libraries have a few important differences:

 * **Moshi has fewer built-in type adapters.** For example, you need to configure your own date
   adapter. Most binding libraries will encode whatever you throw at them. Moshi refuses to
   serialize platform types (`java.*`, `javax.*`, and `android.*`) without a user-provided type
   adapter. This is intended to prevent you from accidentally locking yourself to a specific JDK or
   Android release.
 * **Moshi is less configurable.** There’s no field naming strategy, versioning, instance creators,
   or long serialization policy. Instead of naming a field `visibleCards` and using a policy class
   to convert that to `visible_cards`, Moshi wants you to just name the field `visible_cards` as it
   appears in the JSON.
 * **Moshi doesn’t have a `JsonElement` model.** Instead it just uses built-in types like `List` and
   `Map`.
 * **No HTML-safe escaping.** Gson encodes `=` as `\u003d` by default so that it can be safely
   encoded in HTML without additional escaping. Moshi encodes it naturally (as `=`) and assumes that
   the HTML encoder – if there is one – will do its job.


Download
--------

**Moshi is under development.** The API is not final. Download [the latest .jar][dl] or depend via
Maven:

```xml
<dependency>
  <groupId>com.squareup.moshi</groupId>
  <artifactId>moshi</artifactId>
  <version>0.9.0</version>
</dependency>
```
or Gradle:
```groovy
compile 'com.squareup.moshi:moshi:0.9.0'
```

Snapshots of the development version are available in [Sonatype's `snapshots` repository][snap].


License
--------

    Copyright 2015 Square, Inc.

    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.


 [dl]: https://search.maven.org/remote_content?g=com.squareup.moshi&a=moshi&v=LATEST
 [snap]: https://oss.sonatype.org/content/repositories/snapshots/com/squareup/moshi/
 [okio]: https://github.com/square/okio/
 [okhttp]: https://github.com/square/okhttp
 [gson]: https://github.com/google/gson
 [javadoc]: https://square.github.io/moshi/