How to convert a Map to a String in Java?

General Discussions
1

When I print a Map using System.out.println(map), Java provides a nice string representation in the console. How can I achieve the same result but store it in a variable instead?

Is there a built-in method like Collections.toString(map), or what’s the best way to convert a Java Map to a String without using standard output?

2

Using toString() (Built-in Method)

The simplest way is to use the toString() method, which Java provides for Map objects:

Map<String, Integer> map = new HashMap<>();
map.put("Alice", 25);
map.put("Bob", 30);

String mapAsString = map.toString();
System.out.println(mapAsString);
Output:

{Alice=25, Bob=30}

:white_check_mark: Pros: Simple, built-in, works for most cases.

:x: Cons: Not customizable (e.g., formatting, separators).

3

Using Java Streams (Custom Formatting) If you want a custom string format, use Stream:

String formatted = map.entrySet().stream()
    .map(e -> e.getKey() + "=" + e.getValue())
    .collect(Collectors.joining(", ", "{", "}"));

System.out.println(formatted);
Output:

{Alice=25, Bob=30}

:white_check_mark: Pros: Fully customizable formatting.

:x: Cons: Slightly more complex than toString().

4

Using JSON (For Readability & Data Transfer) If you need structured output, use a JSON library like Jackson:

java
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Edit
import com.fasterxml.jackson.databind.ObjectMapper;

ObjectMapper objectMapper = new ObjectMapper();
String json = objectMapper.writeValueAsString(map);

System.out.println(json);
Output (JSON format):


{"Alice":25,"Bob":30}

:white_check_mark: Pros: Readable, structured, useful for APIs.

:x: Cons: Requires an external library.