Pretty-print a Map in Java

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

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

I want more freedom in my map entry values and am looking for something more like this: key1="value1", key2="value2", key3="value3"

I wrote this little piece of code:

StringBuilder sb = new StringBuilder();
Iterator<Entry<String, String>> iter = map.entrySet().iterator();
while (iter.hasNext()) {
    Entry<String, String> entry = iter.next();
    sb.append(entry.getKey());
    sb.append('=').append('"');
    sb.append(entry.getValue());
    sb.append('"');
    if (iter.hasNext()) {
        sb.append(',').append(' ');
    }
}
return sb.toString();

But I am sure there is a more elegant and concise way to do this.

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

Have a look at the Guava library:

Joiner.MapJoiner mapJoiner = Joiner.on(",").withKeyValueSeparator("=");
System.out.println(mapJoiner.join(map));

Or put your logic into a tidy little class.

public class PrettyPrintingMap<K, V> {
    private Map<K, V> map;

    public PrettyPrintingMap(Map<K, V> map) {
        this.map = map;
    }

    public String toString() {
        StringBuilder sb = new StringBuilder();
        Iterator<Entry<K, V>> iter = map.entrySet().iterator();
        while (iter.hasNext()) {
            Entry<K, V> entry = iter.next();
            sb.append(entry.getKey());
            sb.append('=').append('"');
            sb.append(entry.getValue());
            sb.append('"');
            if (iter.hasNext()) {
                sb.append(',').append(' ');
            }
        }
        return sb.toString();

    }
}

Usage:

Map<String, String> myMap = new HashMap<String, String>();

System.out.println(new PrettyPrintingMap<String, String>(myMap));

Note: You can also put that logic into a utility method.

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>

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)