# Tinystruct Patterns

> Expert guidance for developing with the tinystruct Java framework. Use when working on the tinystruct codebase or any project built on tinystruct — including creating Application classes, @Action-mapped routes, unit tests, ActionRegistry, HTTP/CLI dual-mode handling, the built-in HTTP server, the event system, JSON with Builder/Builders, database persistence with AbstractData, POJO generation, Server-Sent Events (SSE), file uploads, and outbound HTTP networking.

- Skill: `tinystruct/tinystruct-patterns` (Agent Skill, multi-file: 7 files)
- Install (CLI): `npx skillmds@latest add tinystruct/tinystruct-patterns`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tinystruct/tinystruct-patterns/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tinystruct (https://skillmd.com/u/tinystruct)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tinystruct/tinystruct-patterns

---


# tinystruct Development Patterns

Architecture and implementation patterns for building modules with the **tinystruct** Java framework – a lightweight, high-performance framework that treats CLI and HTTP as equal citizens, requiring no `main()` method and minimal configuration.

## Core Principle

**CLI and HTTP are equal citizens.** Every method annotated with `@Action` should ideally be runnable from both a terminal and a web browser without modification. This "dual-mode" capability is the core design philosophy of tinystruct.

## When to Activate

### When to Use

- Creating new `Application` modules by extending `AbstractApplication`.
- Defining routes and command-line actions using `@Action`.
- Handling per-request state via `Context`.
- Performing JSON serialization using the native `Builder` and `Builders` components.
- Working with database persistence via `AbstractData` POJOs.
- Generating POJOs from database tables using the `generate` command.
- Implementing Server-Sent Events (SSE) for real-time push.
- Handling file uploads via multipart data.
- Making outbound HTTP requests with `URLRequest` and `HTTPHandler`.
- Configuring database connections or system settings in `application.properties`.
- Debugging routing conflicts (Actions) or CLI argument parsing.

## How It Works

The tinystruct framework treats any method annotated with `@Action` as a routable endpoint for both terminal and web environments. Applications are created by extending `AbstractApplication`, which provides core lifecycle hooks like `init()` and access to the request `Context`.

Routing is handled by the `ActionRegistry`, which automatically maps path segments to method arguments and injects dependencies. For data-only services, the native `Builder` and `Builders` components should be used for JSON serialization to maintain a zero-dependency footprint. The database layer uses `AbstractData` POJOs paired with XML mapping files for CRUD operations without external ORM libraries.

## Examples

### Basic Application (MyService)
```java
public class MyService extends AbstractApplication {
    @Override
    public void init() {
        this.setTemplateRequired(false); // Disable .view lookup for data/API apps
    }

    @Override public String version() { return "1.0.0"; }

    @Action("greet")
    public String greet() {
        return "Hello from tinystruct!";
    }

    // Path parameter: GET /?q=greet/James  OR  bin/dispatcher greet/James
    @Action("greet")
    public String greet(String name) {
        return "Hello, " + name + "!";
    }
}
```

### HTTP Mode Disambiguation (login)
```java
@Action(value = "login", mode = Mode.HTTP_POST)
public String doLogin(Request<?, ?> request) throws ApplicationException {
    request.getSession().setAttribute("userId", "42");
    return "Logged in";
}
```

### Native JSON Data Handling (Builder + Builders)
```java
import org.tinystruct.data.component.Builder;
import org.tinystruct.data.component.Builders;

@Action("api/data")
public String getData() throws ApplicationException {
    Builders dataList = new Builders();
    Builder item = new Builder();
    item.put("id", 1);
    item.put("name", "James");
    dataList.add(item);

    Builder response = new Builder();
    response.put("status", "success");
    response.put("data", dataList);
    return response.toString(); // {"status":"success","data":[{"id":1,"name":"James"}]}
}
```

### SSE (Server-Sent Events)
```java
import org.tinystruct.http.SSEPushManager;

@Action("sse/connect")
public String connect() {
    return "{\"type\":\"connect\",\"message\":\"Connected to SSE\"}";
}

// Push to a specific client
String sessionId = getContext().getId();
Builder msg = new Builder();
msg.put("text", "Hello, user!");
SSEPushManager.getInstance().push(sessionId, msg);

// Broadcast to all
// Broadcast to all
SSEPushManager.getInstance().broadcast(msg);
```

### File Upload
```java
import org.tinystruct.data.FileEntity;

@Action(value = "upload", mode = Mode.HTTP_POST)
public String upload(Request<?, ?> request) throws ApplicationException {
    List<FileEntity> files = request.getAttachments();
    if (files != null) {
        for (FileEntity file : files) {
            System.out.println("Uploaded: " + file.getFilename());
        }
    }
    return "Upload OK";
}
```

### Database Metadata Operations
`DatabaseOperator` provides direct access to connection-level catalog, schema, and metadata:
```java
import org.tinystruct.data.DatabaseOperator;

DatabaseOperator operator = new DatabaseOperator();
try {
    String catalog = operator.getCatalog();
    String schema = operator.getSchema();
    java.sql.DatabaseMetaData metaData = operator.getMetaData();
    System.out.println("Using catalog: " + catalog + ", schema: " + schema);
} finally {
    operator.close();
}
```

## MCP Server and Tools Integration

tinystruct provides native support for the Model Context Protocol (MCP) starting with SDK version **`1.7.31`**.
The MCP APIs (e.g., `org.tinystruct.mcp.MCPTool`, `org.tinystruct.mcp.MCPServer`, `org.tinystruct.mcp.MCPException`) are included directly in the core dependency:
```xml
<dependency>
    <groupId>org.tinystruct</groupId>
    <artifactId>tinystruct</artifactId>
    <version>1.7.31</version>
</dependency>
```

> **SECURITY WARNING (Prompt Injection):**
> Tool return values are fed directly back into the AI model's context window. You **MUST** validate and sanitize all caller-supplied arguments before including them in the tool's return string. Failure to sanitize inputs can allow an attacker to inject adversarial instructions (Prompt Injection) that override the model's behavior. Always validate length, character sets, and nullity.

**To create an MCP Tool:**
1. Extend `org.tinystruct.mcp.MCPTool`.
2. Annotate operations with `@Action` and declare parameters using `@Argument` within the `arguments` array.
3. Accept parameters as explicit method arguments matching the keys in `@Argument`. (Do **not** use `getContext().getAttribute(...)` for tool arguments).

```java
import org.tinystruct.mcp.MCPTool;
import org.tinystruct.mcp.MCPException;
import org.tinystruct.system.annotation.Action;
import org.tinystruct.system.annotation.Argument;

public class MyCustomTool extends MCPTool {
    public MyCustomTool() {
        super("custom", "A custom tool for demonstrating MCP");
    }

    @Action(
        value = "custom/hello",
        description = "Say hello to someone",
        arguments = {
            @Argument(key = "name", description = "The name to greet", type = "string", optional = false)
        }
    )
    public String hello(String name) throws MCPException {
        // SECURITY: Validate/sanitize tool inputs before returning to the model
        // to prevent prompt injection vulnerabilities.
        if (name == null || name.length() > 50 || !name.matches("^[a-zA-Z0-9 ]+$")) {
            throw new MCPException("Invalid name provided");
        }
        return "Hello, " + name + "!";
    }
}
```

**To deploy an MCP Server:**
1. Extend `org.tinystruct.mcp.MCPServer`.
2. Override `init()` and register your tools using `this.registerTool()`. The framework automatically scans and maps the `@Action` methods.

```java
import org.tinystruct.mcp.MCPServer;

public class MyMCPServer extends MCPServer {
    @Override
    public void init() {
        super.init();
        this.registerTool(new MyCustomTool());
    }

    @Override
    public String version() {
        return "1.0.0";
    }
}
```

Run the server via the dispatcher:
```bash
bin/dispatcher start --import org.tinystruct.system.HttpServer --import com.example.MyMCPServer
```

### Overloaded Tool Methods
tinystruct supports overloaded methods for the same tool name in `MCPTool` (sharing the same tool name but accepting different parameter signatures).
- **Schema Merging**: Input schemas of all overloads with the same name are dynamically merged into a unified JSON schema. Properties are unioned, and required properties are intersected (only fields required across *all* overloads remain marked mandatory).
- **Execution Routing**: When executing a tool, the server iterates sequentially through the available overloaded methods, attempting execution. Each method's schema validation is performed first, and the first overload that validates against the provided arguments successfully executes. If no signature matches or succeeds, the framework throws an appropriate exception.

## Configuration

Settings are managed in `src/main/resources/application.properties`.

```properties
# Database
driver=org.h2.Driver
database.url=jdbc:h2:~/mydb
database.user=sa
database.password=

# Server
default.home.page=hello
server.port=8080
default.server.open_browser=true

# Locale
default.language=en_US

# Session (Redis for clustered environments)
# default.session.repository=org.tinystruct.http.RedisSessionRepository
# redis.host=127.0.0.1
# redis.port=6379

# Programmatic Logging Configuration
logging.enabled=true
logging.level=INFO
org.tinystruct.level=FINE
```

Access config values in your application:
```java
String port = this.getConfiguration("server.port");
```

## Logging and Diagnostics

The framework includes a programmatic wrapper around `java.util.logging` (JUL) that provides beautiful console output and advanced caller tracing out of the box.

- **ANSI Console Colors**: Console output is color-coded based on the log level (red for SEVERE, yellow for WARNING, green for INFO, cyan for CONFIG, and grey for FINE/debug logs).
- **Precise Caller Tracing**: Uses Java's `StackWalker` API to trace the call stack at runtime. It identifies and logs the exact class, method, filename, and line number of the caller that initiated the log (bypassing internal utility and logging layers).
- **Package/Logger Level Overrides**: Set package-specific overrides directly in `application.properties` (e.g., `org.tinystruct.level=FINE`).

## Red Flags & Anti-patterns

| Symptom | Correct Pattern |
|---|---|
| Importing `com.google.gson` or `com.fasterxml.jackson` | Use `org.tinystruct.data.component.Builder` / `Builders`. |
| Using `List<Builder>` for JSON arrays | Use `Builders` to avoid generic type erasure issues. |
| `ApplicationRuntimeException: template not found` | Call `setTemplateRequired(false)` in `init()` for API-only apps. |
| Annotating `private` methods with `@Action` | Actions must be `public` to be registered by the framework. |
| Hardcoding `main(String[] args)` in apps | Use `bin/dispatcher` as the entry point for all modules. |
| Manual `ActionRegistry` registration | Prefer the `@Action` annotation for automatic discovery. |
| Action not found at runtime | Ensure class is imported via `--import` or listed in `application.properties`. |
| CLI arg not visible | Pass with `--key value`; access via `getContext().getAttribute("--key")`. |
| Two methods same path, wrong one fires | Set explicit `mode` (e.g., `HTTP_GET` vs `HTTP_POST`) to disambiguate. |

## Best Practices

1. **Granular Applications**: Break logic into smaller, focused applications rather than one monolithic class.
2. **Setup in `init()`**: Leverage `init()` for setup (config, DB) rather than the constructor. Do NOT call `setAction()` — use `@Action` annotation.
3. **Mode Awareness**: Use the `Mode` parameter in `@Action` to restrict sensitive operations to `CLI` only or specific HTTP methods.
4. **Context over Params**: For optional CLI flags, use `getContext().getAttribute("--flag")` rather than adding parameters to the method signature.
5. **Asynchronous Events**: For heavy tasks triggered by events, use `CompletableFuture.runAsync()` inside the event handler.

## Technical Reference

Detailed guides are available in the `references/` directory:

- [Architecture & Config](references/architecture.md) — Abstractions, Package Map, Properties
- [Routing & @Action](references/routing.md) — Annotation details, Modes, Parameters
- [Data Handling](references/data-handling.md) — Builder, Builders, JSON serialization & parsing
- [Database Persistence](references/database.md) — AbstractData POJOs, CRUD, mapping XML, POJO generation
- [System & Usage](references/system-usage.md) — Context, Sessions, SSE, File Uploads, Events, Networking
- [Testing Patterns](references/testing.md) — JUnit 5 unit and HTTP integration testing

## Reference Source Files (Internal)

- `src/main/java/org/tinystruct/AbstractApplication.java` — Core base class with lifecycle hooks
- `src/main/java/org/tinystruct/system/annotation/Action.java` — Annotation & Modes
- `src/main/java/org/tinystruct/application/ActionRegistry.java` — Routing Engine
- `src/main/java/org/tinystruct/data/component/Builder.java` — JSON object serializer
- `src/main/java/org/tinystruct/data/component/Builders.java` — JSON array serializer
- `src/main/java/org/tinystruct/data/component/AbstractData.java` — Base POJO class with CRUD
- `src/main/java/org/tinystruct/data/Mapping.java` — Mapping XML parser
- `src/main/java/org/tinystruct/data/tools/MySQLGenerator.java` — POJO generator reference
- `src/main/java/org/tinystruct/data/component/FieldType.java` — SQL-to-Java type mappings
- `src/main/java/org/tinystruct/data/component/Condition.java` — Fluent SQL query builder
- `src/main/java/org/tinystruct/http/SSEPushManager.java` — SSE connection management
- `src/main/java/org/tinystruct/system/logging/LogFormatter.java` — Custom log formatter with ANSI console colors and StackWalker-based caller tracing
- `src/main/java/org/tinystruct/system/logging/LoggerConfigurer.java` — Programmatic logging configurator from application properties
- `src/test/java/org/tinystruct/application/ActionRegistryTest.java` — Registry test examples
- `src/test/java/org/tinystruct/system/HttpServerHttpModeTest.java` — HTTP integration test patterns