1. Overview
In this tutorial, we’ll convert a Map to a Spring MultiValueMap and understand it with a clear example.
In the Spring Framework, a MultiValueMap is a specialized map that holds multiple values against a single key. It’s beneficial for handling HTTP request parameters, headers, and in other scenarios where one key might correspond to multiple values. Converting a standard Map to a MultiValueMap can be a common requirement in Spring applications.
2. What Is a MultiValueMap?
A MultiValueMap is an interface Spring provides that extends the Map<K, List
The most commonly used implementation is LinkedMultiValueMap.
3. Ways to Convert a Map to a Spring MultiValueMap
Let’s say we have a Map<String, List
Here’s how we can do that.
We should ensure that our project includes the Spring Framework. If we’re using Maven, we add the following dependency to our pom.xml:
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>6.1.7</version>
</dependency>
As, an initial step, we’ll create a sample Map<String, List
Map<String, List<String>> map = new HashMap<>();
map.put("rollNo", Arrays.asList("4", "2", "7", "3"));
map.put("name", Arrays.asList("John", "Alex", "Maria", "Jack"));
map.put("hobbies", Arrays.asList("Badminton", "Reading novels", "Painting", "Cycling"));
3.1. Using Manual Iteration
We can convert our Map to MultiValueMap using normal iteration:
MultiValueMap<String, String> multiValueMap = new LinkedMultiValueMap<>();
for (Map.Entry<String, List<String>> entry : map.entrySet()) {
multiValueMap.put(entry.getKey(), entry.getValue());
}
The code above converts a Map<String, List
This structure is particularly useful in Spring MVC for handling form data or query parameters with multiple values associated with a single key.
3.2. Using CollectionUtils.toMultiValueMap()
The Spring Framework provides a utility method in CollectionUtils that can directly convert a Map<K, List
MultiValueMap<String, String> multiValueMap = CollectionUtils.toMultiValueMap(map);
3.3. Using Java Streams
Java Streams API can also be utilized to perform the conversion in a more functional programming style:
MultiValueMap<String, String> multiValueMap = map.entrySet()
.stream()
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (oldValue, newValue) -> oldValue, LinkedMultiValueMap::new));
This code converts a Map<String, List
4. Conclusion
In this article, we saw how to convert a Map to a MultiValueMap. By following the steps outlined above, we can easily convert and utilize MultiValueMap in our Spring applications, making our code more versatile and easier to manage when dealing with complex data structures.
We saw multiple ways, and each way has its advantages. It’s important to choose the method that best fits our coding style and application requirements. Each of these approaches will help us efficiently handle scenarios where a key maps to multiple values in Spring applications.
The source code of all these examples is available over on GitHub.