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

Arrays.toString(map.entrySet().toArray())

Answer 2

String result = objectMapper.writeValueAsString(map) - as simple as this!

Result:

{"2019-07-04T03:00":1,"2019-07-04T04:00":1,"2019-07-04T01:00":1,"2019-07-04T02:00":1,"2019-07-04T13:00":1,"2019-07-04T06:00":1 ...}

P.S. add Jackson JSON to your classpath.

Answer 3

Simple and easy. Welcome to the JSON world. Using Google's Gson:

new Gson().toJson(map)

Example of map with 3 keys:

{"array":[null,"Some string"],"just string":"Yo","number":999}

Answer 4

When I have org.json.JSONObject in the classpath, I do:

Map<String, Object> stats = ...;
System.out.println(new JSONObject(stats).toString(2));

(this beautifully indents lists, sets and maps which may be nested)

Answer 5

Since java 8 there is easy way to do it with Lambda:

yourMap.keySet().forEach(key -> {
    Object obj = yourMap.get(key);
    System.out.println( obj);
}

Answer 6

public void printMapV2 (Map <?, ?> map) {
    StringBuilder sb = new StringBuilder(128);
    sb.append("{");
    for (Map.Entry<?,?> entry : map.entrySet()) {
        if (sb.length()>1) {
            sb.append(", ");
        }
        sb.append(entry.getKey()).append("=").append(entry.getValue());
    }
    sb.append("}");
    System.out.println(sb);
}