---

# (DD24) Business Logic — OwnerController.showOwner() [9 LOC]

| Field | Value |
|-------|-------|
| Fully Qualified Name | `org.springframework.samples.petclinic.owner.OwnerController` |
| Layer | Controller |
| Module | `owner` (Package: `org.springframework.samples.petclinic.owner`) |

## 1. Role

### OwnerController.showOwner()

This method is the primary read-only entry point for the owner details screen. It resolves a single owner record from the owner repository using the path variable `ownerId`, then prepares a `ModelAndView` for the Thymeleaf view `owners/ownerDetails`. In business terms, it supports the “display owner profile” use case by retrieving the selected customer record and exposing it to the UI for review of ownership details, pets, and related information rendered by the view.

The method follows a simple routing-and-delegation pattern: the controller accepts the web request, delegates data retrieval to the repository abstraction, and then packages the domain object into the model for presentation. It has one success path and one failure path. If the owner exists, it is added to the model and returned to the caller. If no owner exists for the supplied identifier, the method fails fast with an `IllegalArgumentException`, preventing the application from rendering an invalid detail page.

This method is a screen-facing controller action rather than a reusable domain service. Its role in the larger system is to bridge HTTP navigation to the owner aggregate and to enforce the assumption that the detail screen must always be backed by an existing owner record. Because it performs a direct lookup and returns a presentation model, it is a classic CRUD read endpoint.

## 2. Processing Pattern (Detailed Business Logic)

```mermaid
flowchart TD
    START(["showOwner(ownerId)"])
    CREATE_MAV(["Create ModelAndView with view owners/ownerDetails"])
    CALL_FIND(["this.owners.findById(ownerId)"])
    CHECK_OWNER(["Owner present?"])
    THROW_ERR(["Throw IllegalArgumentException with not found message"])
    ADD_OBJECT(["mav.addObject(owner)"])
    RETURN_NODE(["Return ModelAndView"])

    START --> CREATE_MAV
    CREATE_MAV --> CALL_FIND
    CALL_FIND --> CHECK_OWNER
    CHECK_OWNER -->|Yes| ADD_OBJECT
    CHECK_OWNER -->|No| THROW_ERR
    ADD_OBJECT --> RETURN_NODE
```

## 3. Parameter Analysis

| No | Parameter Name | Type | Business Description |
|----|---------------|------|---------------------|
| 1 | `ownerId` | `@PathVariable("ownerId") int` | The unique owner identifier extracted from the URL path. It selects which customer profile should be displayed on the owner details screen. Valid values are positive integer owner primary keys; if the ID does not match an existing record, the method stops with an exception instead of returning an empty page. |

**Instance fields / external state read by the method:**
- `this.owners` — the injected owner repository used to locate the owner record.
- The resolved MVC view name `owners/ownerDetails`.

## 4. CRUD Operations / Called Services

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

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|----------------------|
| R | `OwnerRepository.findById` | OwnerRepository | Owner | Calls `findById` in `OwnerRepository` |

Analyze all method calls within this method and classify each as a CRUD operation.
Use the pre-computed evidence above. If SC Code or Entity/DB is missing, try to infer from:
- The **SC Code** (Service Component code, e.g., `EKK0361A010SC`, `EKK1081D010CBS`) — look at the class name of the called method or its containing class.
- The **Entity/DB tables** — search for table name constants (often `KK_T_*` pattern), SQL references, or entity names in the called method's source code.

| CRUD | SC / CBS | SC Code | Entity / DB | Operation Description |
|------|----------|---------|-------------|----------------------|
| R | `findById` | `OwnerRepository` | `Owner` | Reads one owner aggregate by primary key so the detail page can be rendered for the selected customer. |

## 5. Dependency Trace


Trace who calls this method and what this method ultimately calls.
Use the pre-computed evidence and caller search results from Step 2 above.

| # | Caller (Screen/Batch) | Call Chain (Full Path to this Method) | Terminal (SC / CRUD / Entity) |
|---|----------------------|--------------------------------------|----------------------|
| 1 | Screen:OwnerControllerTests | `OwnerControllerTests.showOwner()` -> `OwnerController.showOwner()` | `findById [R] Owner` |

**Instructions:**
- Use `search_files` with pattern `**/*.java` and content_pattern `showOwner` to find all callers.
- For each caller, identify if it's a Screen (class name contains `KKSV*`, `Screen*`), Batch, Controller, or CBS.
- Build the full call chain from the entry point to this method. Each row = one unique entry point. Show ALL found callers (up to 15 rows).
- The Terminal column lists ALL CRUD endpoints reached FROM this method.
- Format terminal as: `methodName [C/R/U/D] EntityOrTableName`
- If a caller class name matches `KKSV\d{4}`, format as `Screen:KKSVxxxx`.

## 6. Per-Branch Detail Blocks

Analyze the method's control flow block by block. Analyze ALL nesting levels — no depth limit.

> Each branch of the control flow is displayed as a hierarchical block structure.

**Block 1** — [START] `(showOwner(@PathVariable("ownerId") int ownerId))` (L167)

> Displays the owner detail screen entry point and initializes the presentation model.

| # | Type | Code |
|---|------|------|
| 1 | SET | `ModelAndView mav = new ModelAndView("owners/ownerDetails");` |
| 2 | CALL | `this.owners.findById(ownerId);` |

**Block 2** — [IF] `(optionalOwner is present)` (L169-L170)

> Success path when the requested owner exists in the repository.

| # | Type | Code |
|---|------|------|
| 1 | EXEC | `optionalOwner.orElseThrow(...)` |
| 2 | SET | `Owner owner = ...;` |
| 3 | EXEC | `mav.addObject(owner);` |
| 4 | RETURN | `return mav;` |

**Block 3** — [ELSE] `(optionalOwner is empty)` (L169-L170)

> Failure path when the requested owner ID does not match any persisted owner.

| # | Type | Code |
|---|------|------|
| 1 | EXEC | `optionalOwner.orElseThrow(() -> new IllegalArgumentException("Owner not found with id: " + ownerId + ". Please ensure the ID is correct "));` |
| 2 | RETURN | `throws IllegalArgumentException` |

## 7. Glossary

Define ALL domain-specific terms, Japanese field names, and technical abbreviations used in this method. This section makes the document accessible to Business Analysts (BA) who may not be familiar with the codebase's naming conventions.

| Term | Type | Business Meaning |
|------|------|------------------|
| `ownerId` | Field | Owner identifier used to look up a single customer profile for the detail page. |
| `Owner` | Entity | Customer/owner aggregate representing a pet owner in the PetClinic domain. |
| `OwnerRepository` | Repository | Persistence abstraction used to read owner records from the database. |
| `ModelAndView` | MVC Type | Spring MVC wrapper containing the view name and model attributes needed to render a screen. |
| `owners/ownerDetails` | View | Thymeleaf template used to display the selected owner’s detail page. |
| `PathVariable` | Web annotation | Maps a value from the request URL path into the controller method parameter. |
| CRUD | Acronym | Create, Read, Update, Delete — standard data access operation categories. |
| `IllegalArgumentException` | Exception | Runtime error raised when the owner ID does not resolve to a valid persisted record. |
| optionalOwner | Technical term | `Optional<Owner>` wrapper used to represent the possible presence or absence of the owner record. |