Paper

Paper is a fast NoSQL data storage for Android that lets you save/restore Java/Kotlin objects using efficient Kryo serialization. Object structure changes handled automatically.

What's new in 2.0

Update internal Kryo serializer to 4.0. The data format is changed, but Paper supports backward data compatibility automatically;
Now 58% less methods count : 4037;
Depends on data structure you may experience faster reading but slower writing.

Add dependency

compile 'io.paperdb:paperdb:2.0'

Initialize Paper

Should be initialized one time in onCreate() in Application or Activity.

Paper.init(context);

It's OK to call it in UI thread. All other methods should be used in background thread.

Save

Save data object. Paper creates separate data file for each key.

Paper.book().write("city", "Lund"); // Primitive
Paper.book().write("task-queue", queue); // LinkedList
Paper.book().write("countries", countryCodeMap); // HashMap

Read

Read data objects. Paper instantiates exactly the classes which has been used in saved data. The limited backward and forward compatibility is supported. See Handle data class changes.

String city = Paper.book().read("city");
LinkedList queue = Paper.book().read("task-queue");
HashMap countryCodeMap = Paper.book().read("countries");

Use default values if object doesn't exist in the storage.

String city = Paper.book().read("city", "Kyiv");
LinkedList queue = Paper.book().read("task-queue", new LinkedList());
HashMap countryCodeMap = Paper.book().read("countries", new HashMap());

Delete

Delete data for one key.

Paper.book().delete("countries");

Completely destroys Paper storage. Requires to call Paper.init() before usage.

Paper.book().destroy();

Use custom book

You can create custom Book with separate storage using

Paper.book("custom-book")...;

Each book is located in separate file folder.

Get all keys

Returns all keys for objects in the book.

List<String> allKeys = Paper.book().getAllKeys();

Handle data structure changes

Class fields which has been removed will be ignored on restore and new fields will have their default values. For example, if you have following data class saved in Paper storage:

class Volcano {
        public String name; // I like Eyjafjallajökull
        public boolean isActive;
    }

And then you realized you need to change the class like:

class Volcano {
        public String name; // I like Eyjafjallajökull
        // public boolean isActive; removed field, who cares about volcano activity
        public Location location; // New field
    }

Then on restore the isActive field will be ignored and new location field will have its default value null.

Exclude fields

Use transient keyword for fields which you want to exclude from saving process.

public transient String tempId = "default"; // Won't be saved

Proguard config

Keep data classes:

-keep class my.package.data.model.** { *; }

alternatively you can implement Serializable for all your data classes and keep all of them using:

-keep class * implements java.io.Serializable { *; }

How it works

Paper is based on the following assumptions:

Saved data on mobile are relatively small;
Random file access on flash storage is very fast.

So each data object is saved in separate file and write/read operations write/read whole file.

The Kryo is used for object graph serialization and to provide data compatibility support.

Benchmark results

Running Benchmark on Nexus 4, in ms:

Benchmark	Paper	Hawk
Read/write 500 contacts	187	447
Write 500 contacts	108	221
Read 500 contacts	79	155

Limitations

Circular references not supported

Apps using Paper

AppDialer – Paper initially has been developed to reduce start up time for AppDialer. Currently AppDialer has the best start up time in its class. And simple no-sql-pain data storage layer like a bonus.

License

Copyright 2015 Aleksey Masny

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.

CCC2016/Paper