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An in-depth look at parameter passing in Spring Boot

Popularity：236 ℃/2024-07-25 16:30:36

An in-depth look at parameter passing in Spring Boot

Parameter passing is a very common and important operation in Spring Boot development. Whether it's processing HTTP requests or passing data between methods, understanding and mastering the various ways of parameter passing can make our code more concise and efficient. Today, we'll dive into parameter passing in Spring Boot.

1. Basics: HTTP request parameters

Handling HTTP request parameters is one of the most basic operations in Spring Boot. We can get these parameters in a variety of ways, including path variables, query parameters, and request bodies.

1.1 Path variables

A path variable is a part of the URL path that is typically used to identify a resource. For example, we have an interface to get user information:

@RestController
@RequestMapping("/users")
public class UserController {

    @GetMapping("/{id}")
    public ResponseEntity<User> getUserById(@PathVariable("id") Long id) {
        // Suppose we have aUserServiceto handle business logic
        User user = (id);
        return (user);
    }
}

In this example, the@PathVariableannotation is used to set theidPartial binding to method parametersidUp.

1.2 Query parameters

The query parameter is the URL of the?The latter part, usually used for filtering or paging. For example, we have an interface to get a list of users:

@RestController
@RequestMapping("/users")
public class UserController {

    @GetMapping
    public ResponseEntity<List<User>> getUsers(@RequestParam(value = "page", defaultValue = "0") int page,
                                               @RequestParam(value = "size", defaultValue = "10") int size) {
        List<User> users = (page, size);
        return (users);
    }
}

In this example, the@RequestParamannotation is used to set the query parameterpagecap (a poem)sizeBinds to method arguments and provides default values.

1.3 Request body

Request bodies are often used to pass complex objects, such as when creating a new resource in a POST request:

@RestController
@RequestMapping("/users")
public class UserController {

    @PostMapping
    public ResponseEntity<User> createUser(@RequestBody User user) {
        User createdUser = (user);
        return ().body(createdUser);
    }
}

In this example, the@RequestBodyannotation is used to bind the JSON data in the request body to the method parametersuserUp.

2. Advanced knowledge: custom parameter parser

Sometimes, the built-in parameter parsing method can't meet our needs, then we can customize the parameter parser.

2.1 Creating custom annotations

First, we need to create a custom annotation:

@Target()
@Retention()
public @interface CurrentUser {
}

2.2 Implementing the HandlerMethodArgumentResolver interface

Next, we need to implement theHandlerMethodArgumentResolverInterface:

public class CurrentUserArgumentResolver implements HandlerMethodArgumentResolver {

    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return () != null;
    }

    @Override
    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer,
                                  NativeWebRequest webRequest, WebDataBinderFactory binderFactory) throws Exception {
        // Suppose we have aUserServiceto get the current user
        return ();
    }
}

2.3 Registering a custom parameter parser

Finally, we need to register the custom parameter parser into the Spring context:

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Autowired
    private UserService userService;

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
        (new CurrentUserArgumentResolver(userService));
    }
}

2.4 Using custom annotations

Now we can use custom annotations in our controller methods:

@RestController
@RequestMapping("/profile")
public class ProfileController {

    @GetMapping
    public ResponseEntity<User> getProfile(@CurrentUser User user) {
        return (user);
    }
}

3. Summary

In Spring Boot, there are several ways to pass parameters, including path variables, query parameters, and request bodies. By understanding and mastering these methods, we can write more concise and efficient code. In addition, when the built-in parameter parsing methods can not meet the demand, we can also customize the parameter parser to achieve more flexible parameter passing.

I hope this blog helps you to better understand parameter passing in Spring Boot. If you have any questions or suggestions, feel free to leave them in the comments section.Happy coding!

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