Pretty-print a Map in Java

Question

I am looking for a nice way to pretty-print a Map.

map.toString() gives me: {key1=value1, key2=value2, key3=value3}

I

Answer 1

I guess something like this would be cleaner, and provide you with more flexibility with the output format (simply change template):

    String template = "%s=\"%s\",";
    StringBuilder sb = new StringBuilder();
    for (Entry e : map.entrySet()) {
        sb.append(String.format(template, e.getKey(), e.getValue()));
    }
    if (sb.length() > 0) {
        sb.deleteCharAt(sb.length() - 1); // Ugly way to remove the last comma
    }
    return sb.toString();

I know having to remove the last comma is ugly, but I think it's cleaner than alternatives like the one in this solution or manually using an iterator.

Answer 2

Using Java 8 Streams:

Map<Object, Object> map = new HashMap<>();

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

System.out.println(content);

Answer 3

I prefer to convert the map to a JSON string it is:

• a standard
• human readable
• supported in editors like Sublime, VS Code, with syntax highlighting, formatting and section hide/show
• supports JPath so editors can report exactly which part of the object you have navigated to

• supports nested complex types within the object

  import com.fasterxml.jackson.core.JsonProcessingException;
  import com.fasterxml.jackson.databind.ObjectMapper;
  
  public static String getAsFormattedJsonString(Object object)
  {
      ObjectMapper mapper = new ObjectMapper();
      try
      {
          return mapper.writerWithDefaultPrettyPrinter().writeValueAsString(object);
      }
      catch (JsonProcessingException e)
      {
          e.printStackTrace();
      }
      return "";
  }
  

Answer 4

Apache libraries to the rescue!

MapUtils.debugPrint(System.out, "myMap", map);

All you need Apache commons-collections library (project link)

Maven users can add the library using this dependency:

<dependency>
    <groupId>commons-collections</groupId>
    <artifactId>commons-collections</artifactId>
    <version>3.2.1</version>
</dependency>