param query spring boot with code examples

Introduction

Spring Boot is a popular Java-based framework used for building applications, and it's widely used for building microservices. One of the key features of Spring Boot is the ability to handle query parameters passed to RESTful APIs, which can be done using various techniques. In this article, we'll look at how to handle query parameters in Spring Boot using various techniques, along with code examples to illustrate each one.

  1. Using @RequestParam

@RequestParam is the simplest way to handle query parameters in a Spring Boot RESTful API. This annotation is used to bind a request parameter to a method argument. The following code example illustrates how to use the @RequestParam annotation in a Spring Boot controller:

@RestController
public class QueryParamController {
  
    @GetMapping("/greet")
    public String greet(@RequestParam(value = "name", defaultValue = "User") String name) {
        return "Hello, " + name + "!";
    }
}

In the code example, the @RequestParam annotation is used to bind the "name" request parameter to the method argument "name". If the "name" parameter is not passed in the request, the default value of "User" is used.

  1. Using @PathVariable

Another way to handle query parameters in Spring Boot is by using the @PathVariable annotation. This annotation is used to bind a URI template variable to a method argument. The following code example illustrates how to use the @PathVariable annotation in a Spring Boot controller:

@RestController
public class PathVariableController {
  
    @GetMapping("/greet/{name}")
    public String greet(@PathVariable String name) {
        return "Hello, " + name + "!";
    }
}

In the code example, the @PathVariable annotation is used to bind the "name" variable in the URI to the method argument "name". The value of "name" is extracted from the URL and passed as an argument to the method.

  1. Using POJOs

Another way to handle query parameters in Spring Boot is by using plain old Java objects (POJOs). In this approach, the query parameters are mapped to a POJO class, which is then used as the method argument. The following code example illustrates how to use POJOs in a Spring Boot controller:

public class Greeting {
    private String name;
  
    public String getName() {
        return name;
    }
  
    public void setName(String name) {
        this.name = name;
    }
}

@RestController
public class PojoController {
  
    @GetMapping("/greet")
    public String greet(Greeting greeting) {
        return "Hello, " + greeting.getName() + "!";
    }
}

In the code example, the Greeting class represents the query parameters, which are mapped to the Greeting object in the method argument. The values of the query parameters are automatically mapped to the Greeting object, and the method can access them using the getter methods.

Conclusion

In this article, we looked at how to handle query parameters in Spring Boot using various techniques, along with code examples to illustrate each one. Whether you use the @RequestParam annotation, the @PathVariable annotation, or POJOs, handling query parameters in Spring Boot is simple
Adjacent Topics

  1. Query Parameter Validation

Query parameters are an essential part of RESTful APIs, and it's important to validate the input provided in the query parameters to ensure that the API functions correctly. In Spring Boot, you can validate query parameters using the Bean Validation API, which provides a set of annotations to validate the input data. The following code example illustrates how to validate query parameters using Bean Validation API in Spring Boot:

public class Greeting {
    @NotBlank
    private String name;
  
    public String getName() {
        return name;
    }
  
    public void setName(String name) {
        this.name = name;
    }
}

@RestController
public class PojoController {
  
    @GetMapping("/greet")
    public String greet(@Valid Greeting greeting) {
        return "Hello, " + greeting.getName() + "!";
    }
}

In the code example, the @NotBlank annotation is used to validate that the "name" field is not empty. If the "name" field is empty, a 400 Bad Request response will be returned.

  1. Query Parameter Customization

By default, Spring Boot automatically maps query parameters to method arguments using the naming convention. However, you can customize the mapping by using the @RequestParam annotation's properties. The following code example illustrates how to customize the mapping of query parameters in Spring Boot:

@RestController
public class QueryParamController {
  
    @GetMapping("/greet")
    public String greet(@RequestParam(value = "user_name", required = false) String name) {
        return "Hello, " + name + "!";
    }
}

In the code example, the "value" property is used to specify the name of the query parameter, which is "user_name" in this case. The "required" property is used to specify whether the query parameter is required or optional. If the "required" property is set to false, the method will still work even if the query parameter is not passed in the request.

  1. Handling Multiple Query Parameters

In some cases, you may need to handle multiple query parameters in a Spring Boot RESTful API. You can handle multiple query parameters by using the @RequestParam annotation multiple times or by using POJOs. The following code example illustrates how to handle multiple query parameters in Spring Boot using POJOs:

public class Greeting {
    private String name;
    private String message;
  
    public String getName() {
        return name;
    }
  
    public void setName(String name) {
        this.name = name;
    }
  
    public String getMessage() {
        return message;
    }
  
    public void setMessage(String message) {
        this.message = message;
    }
}

@RestController
public class PojoController {
  
    @GetMapping("/greet")
    public String greet(Greeting greeting) {
        return greeting.getMessage() + " " + greeting.getName() + "!";
    }
}

In the code example, the Greeting class represents the query parameters, and the method can access the values of the query parameters using the getter methods.

Popular questions

  1. What is a query parameter in Spring Boot?

A query parameter in Spring Boot is a key-value pair that is passed in a URL to retrieve specific data from an API endpoint. Query parameters are used to filter and sort the data returned by an API and can be added to a URL by using the "?" character followed by the key-value pair separated by the "&" character.

  1. How can we pass query parameters in a Spring Boot RESTful API?

In Spring Boot, we can pass query parameters in a RESTful API by adding them to the URL after the endpoint. The following is an example of how to pass query parameters in a Spring Boot RESTful API:

http://localhost:8080/greet?name=John

In the example, the "name" query parameter is passed with the value "John".

  1. How can we retrieve query parameters in a Spring Boot RESTful API?

In Spring Boot, we can retrieve query parameters in a RESTful API by using the @RequestParam annotation. The following code example illustrates how to retrieve query parameters in a Spring Boot RESTful API:

@RestController
public class QueryParamController {
  
    @GetMapping("/greet")
    public String greet(@RequestParam(value = "name") String name) {
        return "Hello, " + name + "!";
    }
}

In the code example, the @RequestParam annotation is used to retrieve the "name" query parameter. The value property of the @RequestParam annotation is used to specify the name of the query parameter.

  1. How can we validate query parameters in a Spring Boot RESTful API?

In Spring Boot, we can validate query parameters in a RESTful API by using the Bean Validation API, which provides a set of annotations to validate the input data. The following code example illustrates how to validate query parameters in a Spring Boot RESTful API:

public class Greeting {
    @NotBlank
    private String name;
  
    public String getName() {
        return name;
    }
  
    public void setName(String name) {
        this.name = name;
    }
}

@RestController
public class PojoController {
  
    @GetMapping("/greet")
    public String greet(@Valid Greeting greeting) {
        return "Hello, " + greeting.getName() + "!";
    }
}

In the code example, the @NotBlank annotation is used to validate that the "name" field is not empty. If the "name" field is empty, a 400 Bad Request response will be returned.

  1. How can we handle multiple query parameters in a Spring Boot RESTful API?

In Spring Boot, we can handle multiple query parameters in a RESTful API by using the @RequestParam annotation multiple times or by using POJOs. The following code example illustrates how to handle multiple query parameters in a Spring Boot RESTful API using POJOs:

public class Greeting {
    private String name;
    private String message;
  
    public String getName() {
        return name;
    }
  
    public void setName(String name) {
        this.name = name;
    }
  
    public String getMessage() {
        return message;
    }
  
   
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