如何使用Spring Boot在Java中使用请求参数

在Spring Boot中，处理请求参数的方法包括：1. 使用@RequestParam获取查询参数，支持必填、可选和默认值；2. 通过List或Map类型接收多个同名参数；3. 结合@ModelAttribute将多个参数绑定到对象；4. 使用@PathVariable提取URL路径中的变量；5. 在POST请求中用@RequestParam处理表单数据；6. 用Map接收所有请求参数。正确选择注解可高效解析请求数据，提升开发效率。

In Spring Boot, handling request parameters is straightforward thanks to built-in annotations and the Spring Web framework. Whether you're building REST APIs or web applications, you'll often need to extract data from incoming HTTP requests. Here's how to use request parameters effectively in Java with Spring Boot.

1. Using @RequestParam for Query Parameters

The most common way to access request parameters (i.e., query parameters in the URL) is with the @RequestParam annotation.

Example:

@RestController
public class UserController {

    @GetMapping("/users")
    public String getUsers(@RequestParam String name) {
        return "Hello, "   name;
    }
}

For a request like GET /users?name=John, this returns Hello, John.

Optional Parameters and Defaults

You can make parameters optional and provide default values:

@GetMapping("/users")
public String getUsers(@RequestParam(required = false) String name) {
    if (name == null) {
        return "Hello, Guest";
    }
    return "Hello, "   name;
}

Or use defaultValue:

@GetMapping("/users")
public String getUsers(@RequestParam(defaultValue = "Guest") String name) {
    return "Hello, "   name;
}

Multiple Parameters

You can have multiple parameters:

@GetMapping("/users")
public String getUsers(
    @RequestParam String name,
    @RequestParam int age) {
    return "Name: "   name   ", Age: "   age;
}

Request: GET /users?name=Alice&age=30

2. Handling Array or List Parameters

If a parameter appears multiple times (e.g., ?hobby=reading&hobby=music), you can bind it to a list or array:

@GetMapping("/users")
public String getUsers(@RequestParam List<String> hobby) {
    return "Hobbies: "   hobby;
}

This will capture all hobby values into a list.

3. Using @RequestParam with Objects (Indirect Binding)

While @RequestParam doesn't directly bind to complex objects, you can map multiple parameters into a DTO by using a custom approach or rely on model attributes in form submissions. However, for query parameters, a common workaround is to use a wrapper class with @ModelAttribute.

Example with @ModelAttribute:

public class UserQuery {
    private String name;
    private Integer age;
    // getters and setters
}

@GetMapping("/users")
public String getUsers(@ModelAttribute UserQuery query) {
    return "Name: "   query.getName()   ", Age: "   query.getAge();
}

Now, GET /users?name=Bob&age=25 will map automatically.

4. Path Variables with @PathVariable

Sometimes you want parameters from the URL path, not the query string:

@GetMapping("/users/{id}")
public String getUser(@PathVariable Long id) {
    return "User ID: "   id;
}

Request: GET /users/123 → returns User ID: 123

You can have multiple path variables:

@GetMapping("/users/{userId}/orders/{orderId}")
public String getOrder(
    @PathVariable Long userId,
    @PathVariable Long orderId) {
    return "User: "   userId   ", Order: "   orderId;
}

5. Request Parameters in POST Requests

@RequestParam also works with form data in POST requests (e.g., application/x-www-form-urlencoded):

@PostMapping("/users")
public String createUser(@RequestParam String name, @RequestParam int age) {
    // Save user logic
    return "User created: "   name   ", "   age;
}

For JSON payloads, use @RequestBody instead — but that’s not request parameters; it's request body parsing.

6. Advanced: Map All Request Parameters

To get all parameters as a map:

@GetMapping("/users")
public String getUsers(@RequestParam Map<String, String> allParams) {
    return "All params: "   allParams;
}

Request: GET /users?name=John&role=admin → returns {name=John, role=admin}

Use Map<string object></string> if you expect lists (e.g., repeated keys).

Key Points to Remember

• Use @RequestParam for query/form parameters.
• Use @PathVariable for values in the URL path.
• Set required = false or use defaultValue for optional parameters.
• Use Map to capture dynamic or unknown parameters.
• For JSON bodies, use @RequestBody, not @RequestParam.

Basically, Spring Boot makes it easy to extract request parameters with clean, readable code. Just match the annotation to your use case, and let Spring handle the parsing.

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