How to enable pretty print JSON output (Jackson)

In this tutorial, we will show you how to use Jackson library to pretty print JSON Object and String in the console and JSP page.

1. Pretty Print JSON Object

Example to convert Object and print its output in JSON format.

		
 User user = new User();
 //...set user data
	
 ObjectMapper mapper = new ObjectMapper();
 System.out.println(mapper.writeValueAsString(user));

But the json output is in compact mode.

{"age":29,"messages":["msg 1","msg 2","msg 3"],"name":"mkyong"}

To enable pretty print, use writerWithDefaultPrettyPrinter.

  ObjectMapper mapper = new ObjectMapper();
  System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(user));

Output

{
  "age" : 29,
  "messages" : [ "msg 1", "msg 2", "msg 3" ],
  "name" : "mkyong"
}

2. Pretty Print JSON String

This is a bit tricky, try to use writerWithDefaultPrettyPrinter again.

  String test = "{\"age\":29,\"messages\":[\"msg 1\",\"msg 2\",\"msg 3\"],\"name\":\"mkyong\"}";
  System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(test));

Output, not what we want, json is still in compact mode.

"{\"age\":29,\"messages\":[\"msg 1\",\"msg 2\",\"msg 3\"],\"name\":\"mkyong\"}"

To solve it, bind the JSON string to Object before pretty print it.

  String test = "{\"age\":29,\"messages\":[\"msg 1\",\"msg 2\",\"msg 3\"],\"name\":\"mkyong\"}";
  Object json = mapper.readValue(test, Object.class);	
  System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(json));

Output

{
  "age" : 29,
  "messages" : [ "msg 1", "msg 2", "msg 3" ],
  "name" : "mkyong"
}

3. Pretty Print JSON in JSP page

To pretty print JSON data in a JSP page or any other HTML page, just wrap the json data with <pre> tag. This example is using Spring MVC and JSP page.

@Controller
@RequestMapping("/anything")
public class AdminController {

  @RequestMapping(method = RequestMethod.GET)
  public ModelAndView index() {

	String test = "{\"age\":29,\"messages\":[\"msg 1\",\"msg 2\",\"msg 3\"],\"name\":\"mkyong\"}";
	Object json = mapper.readValue(test, Object.class);	
	
	ModelAndView modelandView = new ModelAndView("viewname");

	modelandView.addObject("output", mapper.writerWithDefaultPrettyPrinter().writeValueAsString(json));
	
	return modelandViewl;

  }

}

In html page.
<pre>${output}</pre>

References

1. Jackson – High-performance JSON processor.
2. ObjectMapper JavaDoc