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Prefetching-Library

README.md

Prefetching Library

NAPPA Android Prefetch Library

This project contains a library for Android to support prefetching of network requests.

Getting started

Installation

Import library

  • Go to this repository releases page.
  • Download the latest version of the library from NAPPA Prefetching Library v1.x.
  • Open Android Studio.
  • Click on File > New > New Module.
  • Click on Import .JAR/.AAR Package then click Next.
  • Enter the location of the compiled AAR or JAR file then click Finish.

Configure Gradle

Make sure the library is listed at the top of your settings.gradle file, as shown here for a library named "nappa-prefetching-library":

include ':app', :nappa-prefetching-library

Open the app module's build.gradle file and add a new line to the dependencies block as shown in the following snippet:

dependencies {
    implementation project(":nappa-prefetching-library")
}

Click Sync Project with Gradle Files.

Import library dependencies

Import the following libraries to your project

implementation "org.bitbucket.cowwoc:diff-match-patch:1.1"
implementation "com.squareup.okhttp3:okhttp:3.14.8"
implementation "androidx.room:room-runtime:2.2.5"
implementation "androidx.lifecycle:lifecycle-extensions:2.2.0"

Usage

Import the library:

import nl.vu.cs.s2group.nappa.Nappa;

Encapsulate the creation of OkHttpClient instances:

// Default usage
OkHttpClient client = PrefetchingLib.getOkHttp(new OkHttpClient());

// Using builder
OkHttpClient.Builder builder = new OkHttpClient.Builder();
// add build configurations
OkHttpClient client = PrefetchingLib.getOkHttp(builder.build());

Inform the library about the usage of Android Intent Extras:

PrefetchingLib.notifyExtras(intent.getExtras());
startActivity(intent);

Inform the library when navigating between Android Activity:

@Override
protected void onResume() {
    super.onResume();
    PrefetchingLib.setCurrentActivity(this);
}

For existing projects, use the NAPPA Plugin for Android Studio to automatically make these changes and enable NAPPA in the project.

Available prefetching strategies

NAPPA does not impose a specific prefetching strategy, but rather allows for a modular specification of prefetching strategies. The default strategy uses a greedy-based algorithm.

Greedy

The Greedy approach determines which activity successors can benefit the most from prefetching by traversing the ENG tree using a "weight" factor. It recursively considers all successors that can "add value" by prefetching it. The weight is defined as the score that has been calculated in the previous iteration. Therefore, with each recursive iteration, the weight score decreases. There is a fixed threshold to limit the number of candidate URLs to prefetch.

Modifying the library

Required Tools

Implementing a custom prefetching strategy

The prefetching strategies are implemented in the nl.vu.cs.s2group.nappa.prefetch package. These can be used as references on how to implement a new strategy.

To define a new strategy, you must implement the PrefetchStrategy interface and override the method getTopNUrlToPrefetchForNode.

After implementing the strategy, it can be enabled by ... TODO — analyse prefetch library to understand how a prefetching solution is selected and the describe the steps here

After implementing a strategy, please consider sharing it by creating a PR to the official NAPPA repository.

Create a new build

To create a new build with the modifications implemented in the library, click on Build > Make Project. Android Studio places new builds in the directory android_prefetching_lib/build/outputs/aar/. To use this build, repeat the Import Library instructions in the Installation section.

Debug the library

Debug unhandled exceptions outside the main thread

Weird behaviour can be caused by running into an exception in the secondary threads. By default, these don't seem to be logged in the console, which makes difficult to identify them.

To make sure that all unhandled exceptions outside the main thread are logged do the following steps:

  • Open the Breakpoints dialog (Run > View Breakpoints or Ctrl + Shift + F8)
  • In the left panel click on Java Exception Breakpoint > Any Exception
  • Check the option Enabled
  • Uncheck the option Suspend (unless you want to debug values there)
  • Uncheck the option Caught exception (the launcher and class loader exceptions are caught and handled internally by the JVM.)
  • Run the application in debug mode
  • Any unhandled exception will be logged in the Debug window

Debug the database data

Using DB Browser for SQLite

This is an external client for reading database files. Download it at sqlitebrowser.

In Android Studio, go to:

View > Tool Windows > Device File Explorer

This will open a panel with the emulator files. To access this panel the emulator must be first launched. In this panel, go to:

data > data > [application package name] > databases

You should see 3 files:

  • nappa.db
  • nappa.db-shm
  • nappa.db-wal

Select all 3, right click and save as. Open DB Browser for SQLite. Click on Open Database, go to the directory you saved the files and select nappa.db. Click in the Browser Data tab. You can now verify the data saved by the NAPPA Library.

Using Room

You can use the defined DAO Room classes or create your own functions