Java

Updated July 07, 2021

Before you get started learning about Java algorithm development, make sure you go through our Getting Started Guide to learn how to create your first algorithm, understand permissions available, versioning, using the CLI, and more.

Table of contents

Available libraries
Write your first algorithm
Managing dependencies
I/O for your algorithms
Error handling
Publishing Algorithmia Insights
Algorithm checklist
Publish algorithm
Conclusion and resources

Available libraries

Algorithmia makes a number of libraries available to make algorithm development easier.

The full Java 11 language and standard library is available for you to use in your algorithms.

Furthermore, algorithms can call other algorithms and manage data on the Algorithmia platform via the Algorithmia Java Client.

Write your first algorithm

If you’ve followed the Getting Started Guide, you’ll notice in your algorithm editor, there is boilerplate code that returns “Hello” and whatever you input to the console.

The main thing to note about the algorithm is that it’s wrapped in the apply() function.

The apply() function defines the input point of the algorithm. We use the apply() function in order to make different algorithms standardized. This makes them easily chained and helps authors think about designing their algorithms in a way that makes them easy to leverage and predictable for end users.

Go ahead and remove the boilerplate code below that’s inside the apply() function because we’ll be writing a different algorithm in this tutorial:

Algorithm console Java

Managing dependencies

Algorithmia supports adding 3rd party dependencies via Maven packages. Specifically, any packages from Maven Central can be added to algorithms.

On the algorithm editor page there is a button on the top right that says “Dependencies”. Click that button and you’ll see a modal window:

Java Dependency File

If you have any dependencies you can add them by typing in the package name to the dependency file in the following form:

<dependency org="{GroupID}" name="{ArtifactID}" rev="{Version}" conf="default" changing="true"/>

For example, to make use of the Apache Commons Math version 3.4.1 library, you would include the line:

<dependency org="org.apache.commons" name="commons-math3" rev="3.4.1" conf="default" changing="true"/>

in the dependencies file and add the line

import org.apache.commons.math3.*;

in the main file.

The Algorithmia dependency is already installed for your convenience. For more information about Algorithmia’s Maven package visit Java Client Docs

This guide won’t depend on any external dependencies so you can close the dependencies window.

I/O for your algorithms

Now let’s get started on the hands-on portion of the guide:

The first algorithm that we’ll create will take a JSON formatted object passed as input by the user which is deserialized into a Java object before the algorithm is called.

It will output a JSON formatted object which the user will consume with an API call to the algorithm path which is found at the bottom of the algorithm description page.

This path is based on your Algorithmia user name and the name of your algorithm, so if you are “AdaDeveloper” and your algorithm is “TokenizeText”, then the path for version 0.1.1 of your algorithm will be AdaDeveloper/TokenizeText/0.1.1

Working with basic data structures

Below is a code sample showing how to create an algorithm working with basic user input.

You’ll also see some error handling within the algorithm, but we recommend that you take a look at our Better Error Handling Guide for more information.

This example shows how to get the value of the key “URL” from a Map object that the user passes in when calling the algorithm:

package algorithmia.test_java;

import com.algorithmia.*;
import com.algorithmia.algo.*;
import com.algorithmia.data.*;
import com.google.gson.*;
import java.util.*;

public class test_java {
    // Note that you don't pass in your API key when creating an algorithm
    AlgorithmiaClient client = Algorithmia.client();
    // The input and output of apply() automatically turns into JSON
    public String apply(Map<String,String> dict) throws Exception{
        return dict.get("URL");
    }
}

Go ahead and type or paste the code sample above in the Algorithmia code editor after removing the “Hello World” code.

Now compile the new code sample and when that’s done test the code in the console by passing in the input and hitting enter on your keyboard:

{"URL": "some/path/somefile.txt"}

You should see the value from the key returned in the console:

"some/path/somefile.txt"

Working with data stored on Algorithmia

This next code snippet shows how to create an algorithm working with a data file that a user has stored using Algorithmia’s Hosted Data Source.

Files stored in Hosted Data must be transferred into the algorithm before use, via the getFile method. Alternately, their contents can be transferred using getString, getJson, or getBytes.

Prerequisites

If you wish to follow along working through the example yourself, create a text file that contains any unstructured text such as a chapter from a public domain book or article. We used a chapter from Burning Daylight, by Jack London which you can copy and paste into a text file. Or copy and paste it from here: Chapter One Burning Daylight, by Jack London. Then you will can upload it into one of your Data Collections.

This example shows how to create an algorithm that takes a user’s file which is stored in a data collection on the Algorithmia platform. It then splits up the text into sentences and then splits those sentences up into words:

package algorithmia.test_java;

import com.algorithmia.*;
import com.algorithmia.algo.*;
import com.algorithmia.data.*;
import com.google.gson.*;
import java.util.*;

public HashMap apply(Map<String,String> dict) {
    // Take user input of URL and return text split up as words.
    // Note that you don't pass in your API key when creating an algorithm
    AlgorithmiaClient client = Algorithmia.client();
    String text_file = dict.get("URL");
    List<String> all_words = new ArrayList();
    String text = new String();
    try {
        if (client.file(text_file).exists() == true) {
            // Get the contents of the file as a string.
            text = client.file(text_file).getString();
            // Split the contents of the file by the sentences.
            String[] sentences = text.split("\\.");
            // Break down each sentence of the array.
            for( String sentence : sentences ) {
                String[] words = sentence.split("[ ]");
                all_words.add(Arrays.toString(words));
            }

        } else {
            System.out.println("Please check that your file exists");
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
    HashMap<String, Object> map = new HashMap<>();
    map.put("words", all_words);
    map.put("text", text);
    System.out.println(map);
    return map;
}

After you paste the above code into the Algorithmia code editor you can compile and then test the example by passing in a file that you’ve hosted in Data Collections.

Following the example below replace the path to your data collection with your user name (it will appear already if you are logged in), data collection name, and data file name which you can find under “My Collections” in Data Collections:

{"user_file": "data://YOUR_USERNAME/data_collection_dir/data_file.txt"}

This guide uses a chapter from the public domain book Burning Daylight, by Jack London, but for brevity we’ll only show the first sentence in “text” and “words”:

{"text": "It was a quiet night in the Shovel.", "words": [['It', 'was', 'a', 'quiet', 'night', 'in', 'the', 'Shovel']]}

When you are creating an algorithm be mindful of the data types you require from the user and the output you return to them. Our advice is to create algorithms that allow for a few different input types such as a file, a sequence or a URL.

Automatic JSON parsing

package algorithmia.docs.Example;
import com.algorithmia.*;

public class Example {
    public String apply(Map<String,String> dict, String key) {
        return dict.get(key);
    }
}

By default, Algorithmia uses Google’s GSON library for converting JSON to and from native Java objects. You can specify the input and output types of your algorithm simply by setting the parameters and return type of your apply() method.

This example shows a function that takes two parameters, a Map from Strings to Strings (dict) and another String (key), and returns another String.

Algorithmia can automatically parse many types of native Java objects to and from JSON: Integers, Lists, Arrays, Maps, and many others. In many cases it can also parse arbitrary user-defined Java Classes to and from JSON. See the Gson User Guide for reference.

Custom JSON parsing

If you want more control over parsing, then use a single apply method accepting a String and give it the @AcceptsJson annotation (from the com.algorithmia.algo package).

package algorithmia.Example

import com.algorithmia.*;
import com.algorithmia.algo.*;
import com.algorithmia.data.*;

public class JavaTest {
    @AcceptsJson
    public String apply(String input) throws Exception {
        // Parse JSON here
    }
}

If you have more than 1 apply method, or your apply method does not take a String as an argument then you will receive an error message at runtime. Also note that passing in a String "foo" becomes serialized to JSON like "\"foo\"".

On the other hand, if GSON doesn’t serialize your output response to JSON correctly (or you want to do some custom serialization) you can add an @ReturnsJson to your apply method and return a serialized JSON String.

package algorithmia.Example

import com.algorithmia.*;
import com.algorithmia.algo.*;
import com.algorithmia.data.*;

public class JavaTest {
    @ReturnsJson
    public String apply(String input) throws Exception {
        // Do some work
        // Return a JSON string
    }
}

If you use @ReturnsJson but don’t return a valid JSON string, your algorithm will return a JSON parsing error.

Working with directories

While running, algorithms have access to a temporary filesystem located at /tmp, the contents of which do not persist across calls to the algorithm. While the Data API allows you to get the contents of the files you want to work with as JSON, a string, or raw bytes, in some cases you might need your algorithm to read and write files locally. This can be useful as a temporary location to store files downloaded from Hosted Data, such as raw data for processing or models to be loaded into your algorithms. It can also be used to write new files before uploading them via the Data API.

For reference, this gist provides an example of iterating over data in a directory, processing it, and writing new data to a file, while this template for ALBERT and Tensorflow provides an example of using the /tmp directory to load a model.

Writing files for the user to consume

Sometimes it is more appropriate to write your output to a file than to return it directly to the caller. In these cases, you may need to create a temporary file, then copy it to a Data URI (usually one which the caller specified in their request, or a Temporary Algorithm Collection):

// {"target_file":"data://username/collection/filename.txt"}
String file_uri = dict.get("target_file");
File tempfile = new File("/tmp/"+UUID.randomUUID()+".tmp");
save_some_output_to(tempfile);
client.file(file_uri).put(tempfile);

Calling other algorithms and managing data

To call other algorithms or manage data from your algorithm, use the Algorithmia Java Client which is automatically available to any algorithm you create on the Algorithmia platform. For more detailed information on how to work with data see the Data API docs and learn about Algorithmia’s Hosted Data Source.

Here is an example of creating an algorithm that relies on data from another algorithm:

You may call up to 24 other algorithms, either in parallel or recursively.

package algorithmia.test_java;

import com.algorithmia.*;
import com.algorithmia.algo.*;
import com.algorithmia.data.*;
import com.google.gson.*;
import java.util.*;

public HashMap apply(Map<String,String> dict) {
    // Take user input of URL and return text split up as words.
    // Note that you don't pass in your API key when creating an algorithm
    AlgorithmiaClient client = Algorithmia.client();
    String input_url = dict.get("URL");
    String text = new String();
    List<String> all_words = new ArrayList();
    if (input_url.startsWith("http:") || input_url.startsWith("https:")) {
        try {
            Algorithm algo = client.algo("algo://util/Url2Text/0.1.4");
            AlgoResponse result = algo.pipe(input_url);
            text = result.asJsonString();
            // Split the contents of the file by the sentences.
            String[] sentences = text.split("\\.");
            // Break down each sentence of the array.
            for( String sentence : sentences ) {
                String[] words = sentence.split("[ ]");
                all_words.add(Arrays.toString(words));
            }

        } catch (APIException ex) {
            System.out.println("API Exception: " + ex.getMessage());
        }
        catch (AlgorithmException ex) {
            System.out.println("API Exception: " + ex.getMessage());
        }
    } else {
        System.out.println("Please pass in a valid URL");
    }
    HashMap<String, Object> map = new HashMap<>();
    map.put("result", all_words);
    System.out.println(map);
    return map;
}

Go ahead and try the above code sample in the Algorithmia code editor and then type the input into the console:

{"URL": "http://github.com"}

This returns a Map of an ArrayList of words:

Run basic algorithm in console

As you can see from these examples, fields that are passed into your algorithm by the user such as scalar values and sequences such as lists, maps, arrays and bytearray (binary byte sequence such as an image file) can be handled as you would any Java data structure within your algorithm.

Note: Binary data is passed using byte[] and for more information check out the API Docs.

For an example that takes and processes image data check out the Places 365 Classifier’s source code.

Some older algorithms use our deprecated Java client. If it has an import from the algorithmia package instead of the com.algorithmia package, that means it is using the deprecated client.

Error handling

throw new AlgorithmException("Invalid graph structure");

Algorithms can throw any exception, and they will be returned as an error via the Algorithmia API. If you want to throw a generic exception message, use an AlgorithmException.

For more information on error handling see the Better Error Handling Guide.

Publishing Algorithmia Insights

This feature is available to Algorithmia Enterprise users only.

Inference-related metrics (a feature of Algorithmia Insights) can be reported via using the report_insights method of the Algorithmia client.

Depending on your algorithm, you might want to report on the algorithm payload for each API call (such as the features or number of features), the output of the algorithm to monitor data distributions of predictions, or probability of each inference.

In the case of an example credit scoring model, shown in this demo for Algorithmia Insights, reported metrics include the algorithm predictions:

// Report Algorithmia Insights
client.reportInsights(new HashMap<String,Object>() { {
    put("risk_score", risk_score);
    put("approved", approved);
} });

// Sample model output that is pushed to Insights
{
  "approved": 1,
  "risk_score": 0.08
}

Algorithm checklist

Before you are ready to publish your algorithm it’s important to go through this Algorithm Checklist and check out this blog post for Advanced Algorithm Development .

Both links will go over important best practices such as how to create a good algorithm description, add links to external documentation and other important information.

Publish algorithm

Once you’ve developed your algorithm, you can publish it and make it available for others to use.

On the upper right hand side of the algorithm page you’ll see a purple button “Publish” which will bring up a modal:

Publish an algorithm

In this modal, you’ll see a Changes tab, a Sample I/O tab, and one called Versioning.

Changes shows you your commit history and release notes.

Sample I/O is where you’ll create your sample input and output for the user to try under Try the API in the Run tab. When you add a sample input, make sure to test it out with all the inputs that you accept since users will be able to test your algorithm with their own inputs.

Under the Versioning tab, you can select whether your algorithm will be for public use or private use as well as set the royalty. The algorithm can either be royalty-free or charge per-call. If you opt to have the algorithm charge a royalty, as the author, you will earn 70% of the royalty cost.

Check out Algorithm Pricing for more information on how much algorithms will cost to run.

Under Semantic Versioning you can choose which kind of release your change should fall under: Major, Minor, or Revision.

If you are satisfied with your algorithm and settings, go ahead and hit publish. Congratulations, you’re an algorithm developer!

Conclusion and resources

In this guide we covered how to create an algorithm, work with different types of data and learned how to publish an algorithm.

For more resources:

Developer Center

Resources to get you started with Algorithmia