Step by Step Guide to Building an Expensify API Integration in Java

Introduction

Hey there, fellow developer! Ready to dive into the world of expense management? Let's build an Expensify API integration in Java. This guide will walk you through the process, assuming you're already familiar with Java and API integrations. We'll keep things concise and focused on the good stuff.

Prerequisites

Before we jump in, make sure you've got:

• A Java development environment set up
• An Expensify account with API credentials
• Your favorite HTTP client library (we'll use OkHttp in this guide)

Setting up the project

First things first, let's get our project ready:

1. Create a new Java project in your IDE
2. Add the OkHttp dependency to your pom.xml:

<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>4.10.0</version>
</dependency>

Authentication

Expensify uses a simple authentication method. You'll need your API credentials:

private static final String PARTNER_USER_ID = "your_partner_user_id";
private static final String PARTNER_USER_SECRET = "your_partner_user_secret";

Making API requests

Let's create a basic method to send requests to Expensify:

private static String sendRequest(String requestJson) throws IOException {
    OkHttpClient client = new OkHttpClient();
    MediaType JSON = MediaType.get("application/json; charset=utf-8");
    RequestBody body = RequestBody.create(requestJson, JSON);
    Request request = new Request.Builder()
        .url("https://integrations.expensify.com/Integration-Server/ExpensifyIntegrations")
        .post(body)
        .build();
    try (Response response = client.newCall(request).execute()) {
        return response.body().string();
    }
}

Core API operations

Now, let's implement some core operations:

Creating an expense

public static void createExpense(String merchant, double amount) throws IOException {
    String requestJson = String.format(
        "{\"type\":\"create\",\"credentials\":{\"partnerUserID\":\"%s\",\"partnerUserSecret\":\"%s\"},\"inputSettings\":{\"type\":\"expenses\",\"employeeEmail\":\"[email protected]\",\"transactionList\":[{\"merchant\":\"%s\",\"amount\":%f,\"created\":\"2023-05-01\"}]}}",
        PARTNER_USER_ID, PARTNER_USER_SECRET, merchant, amount
    );
    String response = sendRequest(requestJson);
    System.out.println("Create expense response: " + response);
}

Retrieving expenses

public static void getExpenses() throws IOException {
    String requestJson = String.format(
        "{\"type\":\"get\",\"credentials\":{\"partnerUserID\":\"%s\",\"partnerUserSecret\":\"%s\"},\"inputSettings\":{\"type\":\"expenses\",\"employeeEmail\":\"[email protected]\",\"limit\":10}}",
        PARTNER_USER_ID, PARTNER_USER_SECRET
    );
    String response = sendRequest(requestJson);
    System.out.println("Get expenses response: " + response);
}

Advanced features

Handling pagination

When retrieving large sets of data, you'll need to handle pagination:

public static void getAllExpenses() throws IOException {
    int offset = 0;
    int limit = 100;
    boolean hasMore = true;

    while (hasMore) {
        String requestJson = String.format(
            "{\"type\":\"get\",\"credentials\":{\"partnerUserID\":\"%s\",\"partnerUserSecret\":\"%s\"},\"inputSettings\":{\"type\":\"expenses\",\"employeeEmail\":\"[email protected]\",\"limit\":%d,\"offset\":%d}}",
            PARTNER_USER_ID, PARTNER_USER_SECRET, limit, offset
        );
        String response = sendRequest(requestJson);
        // Process the response here
        System.out.println("Expenses batch: " + response);

        // Check if there are more results
        hasMore = response.contains("\"hasMore\":true");
        offset += limit;
    }
}

Testing the integration

Don't forget to test your integration! Here's a simple example:

public static void main(String[] args) {
    try {
        createExpense("Coffee Shop", 4.50);
        getExpenses();
        getAllExpenses();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

Best practices and optimization

• Respect rate limits: Expensify has rate limits, so be sure to implement proper throttling.
• Cache responses when appropriate to reduce API calls.
• Use connection pooling in OkHttp for better performance.

Conclusion

And there you have it! You've just built a basic Expensify API integration in Java. Remember, this is just the beginning – there's so much more you can do with the Expensify API. Keep exploring, keep coding, and most importantly, keep those expenses in check!

Happy coding, and may your expense reports always balance!