Paper

Paper is a fast NoSQL-like storage for Java/Kotlin objects on Android with automatic schema migration support.

What's new in 2.5

(!) This update contains critical fixes, please update your project ASAP!

• Fixed crash on reading data saved with Paper 1.x.
• Fixed potential data loss on failed read attempt.

What's new in 2.1

• Fixed exception potentially causing data corruption on Android N+ (for targetSdkVersion=25+);
• New API:
  • book.lastModified(key) to get last data modification timestamp;
  • Paper.setLogLevel() or book.setLogLevel() to set log level for internal Kryo serializer;

Thanks @aaronpoweruser and @fiskurgit for contrib!

Add dependency

compile 'io.paperdb:paperdb:2.5'

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.

Save

Save any data objects, Map, List, HashMap etc. including all the internal data hierarchy. Paper creates separate data file for each key.

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

Read

Read data objects, the instantiated class is exactly the one used to save data. Limited changes to the class structure are handled automatically. 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;
    public boolean isActive;
}

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

class Volcano {
    public String name;
    // public boolean isActive; removed field
    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 your data classes from modification by Proguard:

-keep class your.app.data.model.** { *; }

also 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:

• Datasets on mobile devices are small and usually don't have relations in between;
• Random file access on flash storage is very fast;

Paper saves each object for given key in a separate file and every write/read operations write/read the 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	sqlite
Read/write 500 contacts	187	447
Write 500 contacts	108	221
Read 500 contacts	79	155

Limitations

• Circular references are not supported

Apps using Paper

• AppDialer – Paper initially has been developed as internal lib 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.