How do I get the compact/minified form of pretty-printed JSON in Java?

Jackson allows you to read from a JSON string, so read the pretty-printed string back into Jackson and then output it again with pretty-print disabled.

See converting a String to JSON.

Simple Example

String prettyJsonString = "{ \"Hello\" : \"world\"}";

ObjectMapper objectMapper = new ObjectMapper();
JsonNode jsonNode = objectMapper.readValue(prettyJsonString, JsonNode.class);

System.out.println(jsonNode.toString());

Requires

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.5.3</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.5.3</version>
</dependency>