Custom Feeders

Overview

Custom feeders generate unlimited, realistic data on-the-fly without pre-built CSV files.

Use cases: - Generate unique email addresses - Generate valid credit card numbers - Generate realistic timestamps - Generate data with constraints (age >18, balance >0) - Generate data that changes over time

CSV Feeders vs Custom Feeders

CSV Feeder (Limited)

csv("data/users.csv")
// ✓ Simple
// ✓ Easy to set up
// ✗ Limited to rows in file
// ✗ Can't generate unlimited data
// ✗ Can't apply logic/constraints

Custom Feeder (Flexible)

Iterator<Map<String, Object>> feeder = Stream.generate(() -> {
    Map<String, Object> map = new HashMap<>();
    map.put("email", "user" + UUID.randomUUID() + "@example.com");
    return map;
}).iterator();

// ✓ Generate unlimited unique data
// ✓ Apply logic and constraints
// ✓ Generate realistic patterns
// ✓ No file required

Basic Custom Feeder

Template

Iterator<Map<String, Object>> customFeeder = 
    Stream.generate(() -> {
        Map<String, Object> map = new HashMap<>();

        // Generate field 1
        map.put("fieldName1", generateValue1());

        // Generate field 2
        map.put("fieldName2", generateValue2());

        return map;
    }).iterator();

// Use in scenario
.feed(new SequenceFeeder(customFeeder))
.exec(http("Request")
    .get("/endpoint?field1=#{fieldName1}&field2=#{fieldName2}")
)

Example 1: Email Generator

Code

Iterator<Map<String, Object>> emailFeeder = 
    Stream.generate(() -> {
        Map<String, Object> map = new HashMap<>();
        int randomNum = new Random().nextInt(100000);
        map.put("email", "user" + randomNum + "@example.com");
        return map;
    }).iterator();

// Use
.feed(new SequenceFeeder(emailFeeder))
.exec(http("Register")
    .post("/register?email=#{email}")
)

Result

First iteration: email=user42156@example.com
Second iteration: email=user87234@example.com
Third iteration: email=user12389@example.com
(unique every time)

Example 2: Credit Card Generator

Code

Iterator<Map<String, Object>> creditCardFeeder = 
    Stream.generate(() -> {
        Map<String, Object> map = new HashMap<>();
        Random random = new Random();

        // Visa prefix: 4532 (valid test number)
        String cardNum = "4532" + String.format("%012d", random.nextLong() % 1000000000000L);

        map.put("cardNumber", cardNum);
        map.put("expiry", "12/25");
        map.put("cvv", String.format("%03d", random.nextInt(1000)));

        return map;
    }).iterator();

// Use
.feed(new SequenceFeeder(creditCardFeeder))
.exec(http("Payment")
    .post("/payment")
    .body(StringBody("{\"cardNumber\": \"#{cardNumber}\", \"cvv\": \"#{cvv}\"}"))
)

Example 3: Timestamp Generator

Code

Iterator<Map<String, Object>> timestampFeeder = 
    Stream.generate(() -> {
        Map<String, Object> map = new HashMap<>();

        // Current time + random offset (last 7 days)
        long now = System.currentTimeMillis();
        long sevenDaysMs = 7 * 24 * 60 * 60 * 1000L;
        long randomOffset = new Random().nextLong() % sevenDaysMs;
        long timestamp = now - randomOffset;

        map.put("timestamp", new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'")
            .format(new Date(timestamp)));

        return map;
    }).iterator();

// Use
.feed(new SequenceFeeder(timestampFeeder))
.exec(http("Create Event")
    .post("/events")
    .body(StringBody("{\"timestamp\": \"#{timestamp}\"}"))
)

Example 4: Constrained Data (Age >18)

Code

Iterator<Map<String, Object>> personFeeder = 
    Stream.generate(() -> {
        Map<String, Object> map = new HashMap<>();
        Random random = new Random();

        // Generate age between 18 and 80
        int age = 18 + random.nextInt(62);

        // Generate name
        String[] names = {"Alice", "Bob", "Charlie", "Diana", "Eve"};
        String name = names[random.nextInt(names.length)];

        map.put("age", age);
        map.put("name", name);

        return map;
    }).iterator();

// Constraint: Only use if age >= 18
.feed(new SequenceFeeder(personFeeder))
.doIf(session -> Integer.parseInt(session.getString("age")) >= 18)
    .then(
        http("Register Adult")
            .post("/register?name=#{name}&age=#{age}")
    )

Example 5: Realistic Product Names

Code

Iterator<Map<String, Object>> productFeeder = 
    Stream.generate(() -> {
        Map<String, Object> map = new HashMap<>();
        Random random = new Random();

        String[] adjectives = {"Premium", "Ultra", "Deluxe", "Professional", "Standard"};
        String[] nouns = {"Widget", "Gadget", "Tool", "Utility", "Device"};
        String[] categories = {"Pro", "Plus", "Max", "Basic", "Essential"};

        String productName = adjectives[random.nextInt(adjectives.length)] + " " +
                            nouns[random.nextInt(nouns.length)] + " " +
                            categories[random.nextInt(categories.length)];

        double price = 10 + random.nextDouble() * 1000; // $10-$1010

        map.put("productName", productName);
        map.put("price", String.format("%.2f", price));

        return map;
    }).iterator();

Performance Considerations

Good Feeder (Efficient)

Iterator<Map<String, Object>> efficientFeeder = 
    Stream.generate(() -> {
        Map<String, Object> map = new HashMap<>();
        map.put("id", UUID.randomUUID().toString());  // Fast
        return map;
    }).iterator();

Bad Feeder (Inefficient)

Iterator<Map<String, Object>> inefficientFeeder = 
    Stream.generate(() -> {
        // ❌ Creating new objects every iteration
        // ❌ Complex logic
        // ❌ Database calls
        Map<String, Object> map = new HashMap<>();

        // This would slow down the load test
        User user = database.getRandomUser();  // SLOW!
        map.put("userId", user.getId());

        return map;
    }).iterator();

Key Takeaways

  1. Custom feeders generate unlimited data
  2. No file storage needed
  3. Apply logic and constraints
  4. Stream.generate() creates infinite iterator
  5. Keep feeder logic efficient (fast)
  6. Realistic data = realistic load test

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