# Request Mapping and Parameters — Spring Boot

Source: https://www.skillbyai.com/en/spring-boot/w-mapping

> Paths, query strings and bodies.

## @PathVariable, @RequestParam, @RequestBody

`@PathVariable` reads parts of the URL (`/products/{id}`), `@RequestParam` reads query parameters (`?max=1000`, with conversion to types such as BigDecimal), and `@RequestBody` deserialises JSON into an object. Conversion errors produce 400 responses automatically. Keep URLs resource-oriented (nouns, plural), use HTTP methods for actions, and limit result sizes; here a configured maximum page size caps the list.

## Filtering with a query parameter, run

I packaged the demo with mvn package, started it with java -jar on port 8085 and called it with curl; the output is copied from that run. max=1000 returns the two cheaper products, ordered by price by the repository query.

```bash
curl -s "localhost:8085/api/products?max=1000"
```

Output:

```
[{"id":1,"name":"Notebook","price":120.00,"currency":"INR"},{"id":2,"name":"Fountain pen","price":899.00,"currency":"INR"}]
```

## Always cap list endpoints

Unbounded list endpoints are a performance and denial-of-service risk; enforce a maximum page size.

**Quiz:** Which annotation reads ?max=1000 from the URL?

- [ ] @RequestBody
- [ ] @PathVariable
- [x] @RequestParam
- [ ] @Entity

*Answer:* @RequestParam. Query parameters map to @RequestParam.