---

# (DD01) Business Logic — Example.asyncPost() [25 LOC]

| Field | Value |
|-------|-------|
| Fully Qualified Name | `io.github.biezhi.java11.http.Example` |
| Layer | Utility |
| Module | `http` (Package: `io.github.biezhi.java11.http`) |

## 1. Role

### Example.asyncPost()

This method demonstrates an asynchronous HTTP POST submission flow using the Java 11 `HttpClient` API. Business-wise, it prepares a small JSON payload, posts that payload to an external web endpoint, and then handles the asynchronous completion result by either logging the failure stack trace or printing the response body and HTTP status code. The method is not a transactional business service, but a sample integration routine that shows how the application can send outbound requests to a remote HTTP service.

The method follows a simple orchestration pattern: instantiate the supporting objects, serialize a request object into JSON, build an HTTP request, and dispatch it asynchronously. Its role in the larger system is best understood as a reusable technical example or proof-of-concept entry point for HTTP client usage rather than a domain-specific business transaction. Because it uses `sendAsync()` with `whenComplete()` and `join()`, it also demonstrates how the application waits for completion while still modeling a non-blocking request submission workflow.

There are no functional branches based on business constants, service categories, or database state. The only branch is the completion callback outcome, which separates success handling from error handling after the remote call returns.

## 2. Processing Pattern (Detailed Business Logic)

```mermaid
flowchart TD
    START(["asyncPost()"])
    NEW_CLIENT(["Create HttpClient instance"])
    NEW_GSON(["Create Gson instance"])
    NEW_FOO(["Create Foo payload object"])
    SET_NAME(["Set foo.name = \"王爵nice\""])
    SET_URL(["Set foo.url = \"https://github.com/biezhi\""])
    TO_JSON(["gson.toJson(foo)"])
    BUILD_REQUEST(["Build HTTP POST request to https://httpbin.org/post with Content-Type application/json"])
    SEND_ASYNC(["client.sendAsync(request, BodyHandlers.ofString())"])
    WHEN_COMPLETE(["whenComplete(resp, t) callback"])
    IF_ERROR{"t != null?"}
    PRINT_STACK(["t.printStackTrace()"])
    PRINT_BODY(["System.out.println(resp.body())"])
    PRINT_STATUS(["System.out.println(resp.statusCode())"])
    JOIN(["join() waits for completion"])
    END_NODE(["Return"])
    START --> NEW_CLIENT --> NEW_GSON --> NEW_FOO --> SET_NAME --> SET_URL --> TO_JSON --> BUILD_REQUEST --> SEND_ASYNC --> WHEN_COMPLETE --> IF_ERROR
    IF_ERROR -->|Yes| PRINT_STACK --> JOIN --> END_NODE
    IF_ERROR -->|No| PRINT_BODY --> PRINT_STATUS --> JOIN --> END_NODE
```

**CRITICAL — Constant Resolution:**
No project constants are referenced by this method. All branch conditions and literal values are defined directly in the method body.

## 3. Parameter Analysis

| No | Parameter Name | Type | Business Description |
|----|---------------|------|---------------------|
| - | (none) | - | - |

External state read by the method:
- `HttpClient` runtime behavior from the Java platform
- Remote endpoint `https://httpbin.org/post`
- Console output stream via `System.out`
- Standard error output via `Throwable#printStackTrace()`

## 4. CRUD Operations / Called Services

This method does not perform database CRUD operations and does not invoke internal business services. Its only external operation is an outbound HTTP POST to a public echo/test endpoint. The asynchronous completion handler only writes to the console.

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|-----------------------|
| R | `HttpClient.sendAsync` | - | External HTTP endpoint (`https://httpbin.org/post`) | Submits an outbound request and reads the response asynchronously from the remote service |
| R | `whenComplete` callback | - | Console / process output | Reads the completion outcome and prints either the exception stack trace or the response body and status code |

## 5. Dependency Trace

### Pre-computed evidence from code analysis graph:

No screen/batch entry points found within 8 hops. Direct callers found: 1 methods.
Terminal operations from this method: -

| # | Caller (Screen/Batch) | Call Chain (Full Path to this Method) | Terminal (SC / CRUD / Entity) |
|---|----------------------|--------------------------------------|-------------------------------|
| 1 | Utility method in `Example` | `Example.main` -> `asyncPost` | `HttpClient.sendAsync` [R] External HTTP endpoint |

## 6. Per-Branch Detail Blocks

**Block 1** — [SEQUENCE] (L61-L75)

> Create the HTTP client, assemble the JSON payload, and prepare the outbound POST request.

| # | Type | Code |
|---|------|------|
| 1 | SET | `HttpClient client = HttpClient.newHttpClient();` |
| 2 | SET | `Gson gson = new Gson();` |
| 3 | SET | `Foo foo = new Foo();` |
| 4 | SET | `foo.name = "王爵nice";` |
| 5 | SET | `foo.url = "https://github.com/biezhi";` |
| 6 | CALL | `gson.toJson(foo);` |
| 7 | SET | `String jsonBody = gson.toJson(foo);` |
| 8 | CALL | `HttpRequest.newBuilder();` |
| 9 | CALL | `uri(new URI("https://httpbin.org/post"));` |
| 10 | CALL | `header("Content-Type", "application/json");` |
| 11 | CALL | `POST(HttpRequest.BodyPublishers.ofString(jsonBody));` |
| 12 | CALL | `build();` |

**Block 2** — [SEQUENCE] (L76-L84)

> Dispatch the request asynchronously and wait for the callback to complete.

| # | Type | Code |
|---|------|------|
| 1 | CALL | `client.sendAsync(request, HttpResponse.BodyHandlers.ofString())` |
| 2 | CALL | `whenComplete((resp, t) -> { ... })` |
| 3 | CALL | `join();` |

**Block 2.1** — [IF] `(t != null)` (L78)

> If the asynchronous request fails, write the stack trace for diagnostics.

| # | Type | Code |
|---|------|------|
| 1 | EXEC | `t.printStackTrace();` |

**Block 2.2** — [ELSE] `(t == null)` (L80-L83)

> If the remote call succeeds, print the response payload and HTTP status code.

| # | Type | Code |
|---|------|------|
| 1 | EXEC | `System.out.println(resp.body());` |
| 2 | EXEC | `System.out.println(resp.statusCode());` |

**Block 3** — [RETURN] (L85)

| # | Type | Code |
|---|------|------|
| 1 | RETURN | `return;` |

## 7. Glossary

| Term | Type | Business Meaning |
|------|------|------------------|
| `asyncPost` | Method name | Demonstration method for submitting an HTTP POST asynchronously |
| `HttpClient` | Technical term | Java HTTP client used to send outbound web requests |
| `HttpRequest` | Technical term | Immutable request definition used to describe the outbound POST |
| `BodyPublishers.ofString` | Technical term | Converts a string payload into an HTTP request body |
| `BodyHandlers.ofString` | Technical term | Reads the HTTP response body as a string |
| `Gson` | Technical term | JSON serializer used to convert the request object into JSON |
| `Foo` | Class / sample model | Example request payload object with `name` and `url` fields |
| `jsonBody` | Field / variable | Serialized JSON request body sent to the remote endpoint |
| `resp` | Variable | Asynchronous HTTP response object returned by the remote service |
| `t` | Variable | Throwable representing any asynchronous failure |
| `httpbin.org` | External service | Public HTTP test endpoint that echoes HTTP requests |
| `Content-Type` | HTTP header | Declares the payload format as JSON |
| `application/json` | MIME type | Standard media type for JSON payloads |
| `join()` | Technical term | Waits for the asynchronous request chain to finish before returning |
| `printStackTrace` | Technical term | Writes exception diagnostics to the error output stream |
| `statusCode` | Technical term | HTTP response status returned by the server |
| `body` | Technical term | Response payload returned by the remote endpoint |
| `王爵nice` | Literal string | Sample business/name value assigned to the payload's `name` field |
| `https://github.com/biezhi` | Literal string | Sample URL value assigned to the payload's `url` field |