Display All Request Parameters

Get all Request Parameters in Java

In this tutorial, we’ll show you how to get all request parameters in java. Ideally, the server should know the parameter names that was sent by the client browser. I have created a simple Spring Controller that gets a request from the client and redirect the user to another page that displays all his request parameters and its values.

Create A Servlet Controller

In our Controller, we take a parameter HttpServletRequest which contains the client request including its parameters.

@Controller @RequestMapping("/sample") public class SampleController < @RequestMapping(value = "/get", method= RequestMethod.GET) public ModelAndView getParameters(HttpServletRequest request)< Enumeration enumeration = request.getParameterNames(); MapmodelMap = new HashMap<>(); while(enumeration.hasMoreElements()) < String parameterName = enumeration.nextElement(); modelMap.put(parameterName, request.getParameter(parameterName)); >ModelAndView modelAndView = new ModelAndView("sample"); modelAndView.addObject("parameters", modelMap); return modelAndView; > >

To get all request parameters in java, we get all the request parameter names and store it in an Enumeration object. Our Enumeration object now contains all the parameter names of the request. We then iterate the enumeration and get the value of the request given the parameter name.

We store the the name and its value in a Map and add it to a ModelAndView and redirect to sample.jsp. Below is the sample.jsp file:

      
List of Request Parameter Names and its Values
 modelMap = (Map) request.getAttribute("parameters"); for(String key: modelMap.keySet())< out.print(key); out.print(" : "); out.print(modelMap.get(key)); out.print("
"); > %>  

Testing our WebApp

To test it, we type the url in the browser:

http://localhost:8080/sample/get?name=javapointers&language=java&version=8

When we hit Enter, the resulting page is below:

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What is the URL.getQuery() method in Java?

Many candidates are rejected or down-leveled due to poor performance in their System Design Interview. Stand out in System Design Interviews and get hired in 2023 with this popular free course.

The getQuery() method of the URL class can be used to get the query or parameter of a specified URL.

The image below shows the different parts of a URL.

The URL class is present in the java.net package.

Syntax

The syntax of the getQuery() method is shown below.

Parameters

The getQuery() method doesn’t take any parameters.

Return value

The return type of the getQuery() method is string . If the URL doesn’t have any query then null is returned.

Code

The code below shows how to use the getQuery() method in Java.

import java.net.URL;
 
class GetQueryExample  
public static void main( String args[] )  
try  
URL url= new URL("https:// www.educative.io?userid=123&lang=en");
 
//Get Query
 
String query=url.getQuery();
 
System.out.println("The URL is : "+url);
 
System.out.println("\nReference or anchor is : "+ query);
 
> catch (Exception e)  
System.out.println(e);
 
>
 
>
>

Explanation

URL url= new URL("https:// www.educative.io?userid=123&lang=en"); 

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What is the URL.getQuery() method in Java?

Many candidates are rejected or down-leveled due to poor performance in their System Design Interview. Stand out in System Design Interviews and get hired in 2023 with this popular free course.

The getQuery() method of the URL class can be used to get the query or parameter of a specified URL.

The image below shows the different parts of a URL.

The URL class is present in the java.net package.

Syntax

The syntax of the getQuery() method is shown below.

Parameters

The getQuery() method doesn’t take any parameters.

Return value

The return type of the getQuery() method is string . If the URL doesn’t have any query then null is returned.

Code

The code below shows how to use the getQuery() method in Java.

import java.net.URL;
 
class GetQueryExample  
public static void main( String args[] )  
try  
URL url= new URL("https:// www.educative.io?userid=123&lang=en");
 
//Get Query
 
String query=url.getQuery();
 
System.out.println("The URL is : "+url);
 
System.out.println("\nReference or anchor is : "+ query);
 
> catch (Exception e)  
System.out.println(e);
 
>
 
>
>

Explanation

URL url= new URL("https:// www.educative.io?userid=123&lang=en"); 

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Spring @RequestParam Annotation with Examples

This guide covers mapping the request query string parameters to Spring Controller method arguments using @RequestParam annotation.

Overview

Spring Web provides the @RequestParam annotation for extracting and mapping query string parameters of a request into Spring Controller’s method arguments. Without that, we’ll have to pull the parameter values manually from the HttpServletRequest and cast them to variables of the desired types.

Spring, along with the annotation, saves us from manual work. It also provides flexible ways of reading single-value, multi-value, or optional parameters and makes them available as method arguments.

Spring @RequestParam Annotation

Before we see the @RequestParam in action, we will look at the annotation itself.

Spring’s @RequestParam annotation maps request parameters to the arguments of a request handler method in Spring Controllers. We can use this annotation on method parameters to bind request parameters by their names.

Interestingly, this annotation is available in Spring Web and Spring WebFlux annotation-based controllers.

@Target() @Retention(RetentionPolicy.RUNTIME) @Documented public @interface RequestParam < @AliasFor("name") String value() default ""; @AliasFor("value") String name() default ""; boolean required() default true; String defaultValue() default "\n\t\t\n\t\t\n\ue000\ue001\ue002\n\t\t\t\t\n"; >Code language: Java (java)

There are only three attributes in this annotation. The name attribute denotes the name of the request param, and we can omit it if the method and request parameters have the same name. The required attribute represents if the request parameter is mandatory, which is true by default. Lastly, the default attribute can specify a fall-back value of a request parameter, which will be used only when the request parameter isn’t present.

Using @RequestParam

To see the @RequestParam in action, we’ll write a @GetMapping method in a Spring @RestController and execute the endpoint with requests contenting query parameters.

Reading Single Query String Parameter

We want to read a single query string parameter from a request and map it to the controller method argument.

@GetMapping("/data1") public String singleParam(@RequestParam String id) < return "id: " + id; >Code language: Java (java)

Behind the scenes, Spring looks for a query string parameter ‘id‘ and extracts its value from the request. Then it invokes the request handler singleParam(Id) and passes the param value as an argument.

To test this controller, let’s execute the GET /data endpoint with the id request parameter.

~ curl 'http://localhost:8080/data1?id=112' -- id: 112Code language: Bash (bash)

Reading Multiple Query String Parameters

Similarly, if the request has more than one query string parameter, we can use @RequestParam annotation individually on the respective method arguments.

@GetMapping("/data2") public String multiParam( @RequestParam String id, @RequestParam String name) < return "id: " + id + ", name: " + name; >Code language: Java (java)

Our controller reads the id and name parameters from the request.

~ curl 'http://localhost:8080/data2?id=112&name=Jon' -- id: 112, name: JonCode language: Bash (bash)

Executing the respective GET request, we see that both request parameters are mapped correctly.

Mapping Query String Parameters with Specific Type

By default, all the request query string parameters are represented as String. However, our method argument can describe the variable to a specific data type. Interestingly, Spring takes care of this type-casting internally.

For example, our Spring Controller reads a request parameter as a Long value.

@GetMapping("/data3") public String typedParam(@RequestParam Long id) < return "id: " + id; >Code language: Java (java)

If Spring cannot cast the param value, it returns HTTP Status 400 (BAD_REQUEST), as shown.

~ curl -i 'http://localhost:8080/data3?id=abc' -- HTTP/1.1 400 . Code language: Bash (bash)

Reading MultiValue Query String Parameters

Any query string parameter in a request can have multiple values. That means they can appear multiple times in the URL or have comma-separated values. Spring @RequestParam annotation maps such request parameters to a collection- for example, List.

@GetMapping("/data4") public String multiValueParams(@RequestParam List id) < return "id: " + id; >Code language: Java (java)

Alternatively, we can also use an Array type or a Set type. Using the parameter of Set type ensures that the query string has unique values.

Let’s execute a request with a comma-separated multi-value parameter.

~ curl 'http://localhost:8080/data4?id=12,13,15,16' -- id: [12, 13, 15, 16]Code language: Bash (bash)

Or a request having the same parameter multiple times with different values.

~ curl 'http://localhost:8080/data4?id=12&id=13&id=15' -- id: [12, 13, 15]Code language: Bash (bash)

Making Query String Parameters Optional

By default, all the request parameters annotated with the @RequestParam are mandatory. Thus in the previous examples, if we skip a query string parameter from a request, we get a Bad Request response.

~ curl -i 'http://localhost:8080/data4' -- HTTP/1.1 400 . Code language: Bash (bash)

Now, let’s see the three ways of using @RequestParam annotation on optional request parameters.

Using @RequestParam required=false

To support optional query string parameters in a Spring controller, we can use the @RequestParam with the required=false flag.

@GetMapping("/data5") public String optionalParams (@RequestParam(required = false) Long id) < return "id: " + id; >Code language: Java (java)

Now, we can omit the id parameter from our request.

~ curl 'http://localhost:8080/data5' -- id: nullCode language: JavaScript (javascript)

Using @RequestParam with Java Optional

Alternatively, we can use the Java Optional to make a particular query string parameter in a request optional. We can also provide a default value for a missing query string using Java Optional.

@GetMapping("/data6") public String javaOptionalParams (@RequestParam Optional id) < return "id: " + id.orElseGet(() -> "Unknown"); >Code language: Java (java)

The example shows how to use Java Optional to make a Spring Controller request parameter not mandatory.

~ curl 'http://localhost:8080/data6' -- id: UnknownCode language: Bash (bash)

Using @RequestParam defaultValue

Lastly, we can use the defaultValue attribute of the @RequestParam annotation to specify a default value of a request parameter. Spring uses the provided defaultValue only when the actual parameter in the request is absent or empty.

@GetMapping("/data7") public String defaultParams (@RequestParam(defaultValue = "Unknown") String id) < return "id: " + id; >Code language: Java (java)

Let’s test this by executing a GET request without any parameters.

~ curl 'http://localhost:8080/data7' -- id: UnknownCode language: Bash (bash)

Mapping Query String Parameters by Name

In the previous examples, the controller method argument and a request’s respective query string parameter had the same name. Thankfully, we can use the name attribute of Spring @RequestParam when the query string parameter name is different than that of the method argument.

@GetMapping("/data8") public String namedParams (@RequestParam(name = "id") String dataId) < return "dataId: " + dataId; >Code language: Java (java)

Reading Query String Parameters as Java Map

With the Spring @RequestParam annotation, we can collect all the request query string parameters as a HashMap. That is useful when we want to read all the query string parameters and their values together.

@GetMapping("/data9") public String mappedParams (@RequestParam Map dataQuery) < return dataQuery.toString(); >Code language: Java (java)

~ curl 'http://localhost:8080/data9?id=12&year=2034' -- Code language: Bash (bash)

Summary

We have covered using Spring @RequestParam annotation to map query string parameters to controller method arguments. This annotation is available for both Spring MVC and Spring WebFlux.

In this tutorial, we had a detailed overview of the @RequestParam annotation and covered various scenarios of mapping request parameters to controller method arguments.

Please refer to our GitHub Repository for the complete source code of the examples used here.

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