Connecting to Redis cache and working with it

1. Start Redis Server Make sure Redis is running on the default port 6379. Test it: redis-cli ping Expected: PONG ________________________________________
2. Add Dependency For Maven: org.springframework.boot spring-boot-starter-data-redis ________________________________________
3. Configure Redis application.properties spring.data.redis.host=localhost spring.data.redis.port=6379 ________________________________________

4. Define a RedisTemplate Bean (Optional)
   @Configuration
   public class RedisConfig {

   @bean
   public RedisTemplate redisTemplate(
   RedisConnectionFactory connectionFactory) {

   RedisTemplate<String, Object> template =
           new RedisTemplate<>();
   
   template.setConnectionFactory(connectionFactory);
   return template;
   

   }
   }

   ---

5. Use RedisTemplate
   Store Data
   @Service
   public class RedisService {

   @Autowired
   private RedisTemplate redisTemplate;

   public void save(String key, String value) {
   redisTemplate.opsForValue().set(key, value);
   }
   }
   Read Data
   public String get(String key) {
   return (String) redisTemplate.opsForValue().get(key);
   }
   Delete Data
   public void delete(String key) {
   redisTemplate.delete(key);
   }

   ---

6. Controller Example
   @RestController
   @RequestMapping("/redis")
   public class RedisController {

   @Autowired
   private RedisService redisService;

   @PostMapping("/{key}/{value}")
   public String save(
   @PathVariable String key,
   @PathVariable String value) {

   redisService.save(key, value);
   return "Saved";
   

   }

   @GetMapping("/{key}")
   public String get(@PathVariable String key) {
   return redisService.get(key);
   }

   @DeleteMapping("/{key}")
   public String delete(@PathVariable String key) {
   redisService.delete(key);
   return "Deleted";
   }
   }

   ---

7. Caching with Redis
   Enable caching:
   @SpringBootApplication
   @EnableCaching
   public class Application {
   }
   Use cache annotations:
   @Cacheable("users")
   public User getUser(Long id) {
   return userRepository.findById(id).orElse(null);
   }
   @CacheEvict(value = "users", key = "#id")
   public void deleteUser(Long id) {
   userRepository.deleteById(id);
   }

execute Get URL in postman:
http://localhost:8080/book/getAllBookDetails
output:

{
    "id1": 6,
    "author": {
        "authorId": 1,
        "authorName": null,
        "contactNumber": null,
        "state": null
    },
    "name": "PHYTHON"
}

]
REDIS in command prompt:
127.0.0.1:6379> keys *
1) "Books::6"
127.0.0.1:6379>

Step 2:
initialising delete method with
@CacheEvict(value = "Books", key = "#bookIDFromRequest")
@DeleteMapping("/DeleteBookDetails/{bookIDFromRequest}")
public ResponseEntity DeleteBookDetails(@PathVariable int bookIDFromRequest) {
log.info("entering DeleteBookDetails");
String upDateBookStatus= bookService.DeleteBookDetailsService(bookIDFromRequest);
log.info("upDateBookStatus "+upDateBookStatus);
ErrorTemplate error = new ErrorTemplate();
if(upDateBookStatus.equalsIgnoreCase("DeleteBook Failed")){
error.setStatusCode(200);
error.setMessage("book id not found");
return ResponseEntity.status(400).body("Book id not found");
}

---

Common Startup Error
If you see:
Unable to connect to Redis
Connection refused: localhost:
Points to remember

1. Entity class must implements Serializale interface so as to allow @cachale to serialise the response oject.