[java] Pretty-Print JSON in Java

I'm using json-simple and I need to pretty-print JSON data (make it more human readable).

I haven't been able to find this functionality within that library. How is this commonly achieved?

I used org.json built-in methods to pretty-print the data.

JSONObject json = new JSONObject(jsonString); // Convert text to object
System.out.println(json.toString(4)); // Print it with specified indentation

The order of fields in JSON is random per definition. A specific order is subject to parser implementation.

In JSONLib you can use this:

String jsonTxt = JSONUtils.valueToString(json, 8, 4);

From the Javadoc:

Underscore-java has static method U.formatJson(json). Five format types are supported: 2, 3, 4, tabs and compact. I am the maintainer of the project. Live example

import com.github.underscore.lodash.U;

import static com.github.underscore.lodash.Json.JsonStringBuilder.Step.TABS;
import static com.github.underscore.lodash.Json.JsonStringBuilder.Step.TWO_SPACES;

public class MyClass {

    public static void main(String args[]) {
        String json = "{\"Price\": {"
        + "    \"LineItems\": {"
        + "        \"LineItem\": {"
        + "            \"UnitOfMeasure\": \"EACH\", \"Quantity\": 2, \"ItemID\": \"ItemID\""
        + "        }"
        + "    },"
        + "    \"Currency\": \"USD\","
        + "    \"EnterpriseCode\": \"EnterpriseCode\""
        + "}}";
        System.out.println(U.formatJson(json, TWO_SPACES)); 
        System.out.println(U.formatJson(json, TABS)); 
    }
}

Output:

{
  "Price": {
    "LineItems": {
      "LineItem": {
        "UnitOfMeasure": "EACH",
        "Quantity": 2,
        "ItemID": "ItemID"
      }
    },
    "Currency": "USD",
    "EnterpriseCode": "EnterpriseCode"
  }
}
{
    "Price": {
        "LineItems": {
            "LineItem": {
                "UnitOfMeasure": "EACH",
                "Quantity": 2,
                "ItemID": "ItemID"
            }
        },
        "Currency": "USD",
        "EnterpriseCode": "EnterpriseCode"
    }
}    

My situation is my project uses a legacy (non-JSR) JSON parser that does not support pretty printing. However, I needed to produce pretty-printed JSON samples; this is possible without having to add any extra libraries as long as you are using Java 7 and above:

ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine scriptEngine = manager.getEngineByName("JavaScript");
scriptEngine.put("jsonString", jsonStringNoWhitespace);
scriptEngine.eval("result = JSON.stringify(JSON.parse(jsonString), null, 2)");
String prettyPrintedJson = (String) scriptEngine.get("result");

If you are using a Java API for JSON Processing (JSR-353) implementation then you can specify the JsonGenerator.PRETTY_PRINTING property when you create a JsonGeneratorFactory.

The following example has been originally published on my blog post.

import java.util.*;
import javax.json.Json;
import javax.json.stream.*;

Map<String, Object> properties = new HashMap<String, Object>(1);
properties.put(JsonGenerator.PRETTY_PRINTING, true);
JsonGeneratorFactory jgf = Json.createGeneratorFactory(properties);
JsonGenerator jg = jgf.createGenerator(System.out);

jg.writeStartObject()                    // {
    .write("name", "Jane Doe")           //    "name":"Jane Doe",
    .writeStartObject("address")         //    "address":{
        .write("type", 1)                //        "type":1,
        .write("street", "1 A Street")   //        "street":"1 A Street",
        .writeNull("city")               //        "city":null,
        .write("verified", false)        //        "verified":false
    .writeEnd()                          //    },
    .writeStartArray("phone-numbers")    //    "phone-numbers":[
        .writeStartObject()              //        {
            .write("number", "555-1111") //            "number":"555-1111",
            .write("extension", "123")   //            "extension":"123"
        .writeEnd()                      //        },
        .writeStartObject()              //        {
            .write("number", "555-2222") //            "number":"555-2222",
            .writeNull("extension")      //            "extension":null
        .writeEnd()                      //        }
    .writeEnd()                          //    ]
.writeEnd()                              // }
.close();

It seems like GSON supports this, although I don't know if you want to switch from the library you are using.

From the user guide:

Gson gson = new GsonBuilder().setPrettyPrinting().create();
String jsonOutput = gson.toJson(someObject);

Update: new JsonParser().parse(...) is @deprecated

Based on the javadoc for Gson 2.8.6:

No need to instantiate this class, use the static methods instead.

JsonParser static methods:

JsonParser.parseString?(jsonString);
JsonParser.parseReader?(reader);

Packages:

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonParser;

Example:

private Gson GSON = new GsonBuilder().setPrettyPrinting().create();
public static String getPerfectJSON(String unformattedJSON) {
    String perfectJSON = GSON.toJson(JsonParser.parseString(unformattedJSON));
    return perfectJSON;
}

Google Gson dependency using Maven:

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.6</version>
</dependency>

Reference:

• JsonParser is deprecated

In one line:

String niceFormattedJson = JsonWriter.formatJson(jsonString)

The json-io libray (https://github.com/jdereg/json-io) is a small (75K) library with no other dependencies than the JDK.

In addition to pretty-printing JSON, you can serialize Java objects (entire Java object graphs with cycles) to JSON, as well as read them in.

Following the JSON-P 1.0 specs (JSR-353) a more current solution for a given JsonStructure (JsonObject or JsonArray) could look like this:

import java.io.StringWriter;
import java.util.HashMap;
import java.util.Map;

import javax.json.Json;
import javax.json.JsonStructure;
import javax.json.JsonWriter;
import javax.json.JsonWriterFactory;
import javax.json.stream.JsonGenerator;

public class PrettyJson {

    private static JsonWriterFactory FACTORY_INSTANCE;

    public static String toString(final JsonStructure status) {

        final StringWriter stringWriter = new StringWriter();

        final JsonWriter jsonWriter = getPrettyJsonWriterFactory()
                .createWriter(stringWriter);

        jsonWriter.write(status);
        jsonWriter.close();

        return stringWriter.toString();
    }

    private static JsonWriterFactory getPrettyJsonWriterFactory() {
        if (null == FACTORY_INSTANCE) {
            final Map<String, Object> properties = new HashMap<>(1);
            properties.put(JsonGenerator.PRETTY_PRINTING, true);
            FACTORY_INSTANCE = Json.createWriterFactory(properties);
        }
        return FACTORY_INSTANCE;
    }

}

Most of the existing answers either depend on some external library, or requiring a special Java version. Here is a simple code to pretty print a JSON string, only using general Java APIs (available in Java 7 for higher; haven't tried older version although).

The basic idea is to tigger the formatting based on special characters in JSON. For example, if a '{' or '[' is observed, the code will create a new line and increase the indent level.

Disclaimer: I only tested this for some simple JSON cases (basic key-value pair, list, nested JSON) so it may need some work for more general JSON text, like string value with quotes inside, or special characters (\n, \t etc.).

/**
 * A simple implementation to pretty-print JSON file.
 *
 * @param unformattedJsonString
 * @return
 */
public static String prettyPrintJSON(String unformattedJsonString) {
  StringBuilder prettyJSONBuilder = new StringBuilder();
  int indentLevel = 0;
  boolean inQuote = false;
  for(char charFromUnformattedJson : unformattedJsonString.toCharArray()) {
    switch(charFromUnformattedJson) {
      case '"':
        // switch the quoting status
        inQuote = !inQuote;
        prettyJSONBuilder.append(charFromUnformattedJson);
        break;
      case ' ':
        // For space: ignore the space if it is not being quoted.
        if(inQuote) {
          prettyJSONBuilder.append(charFromUnformattedJson);
        }
        break;
      case '{':
      case '[':
        // Starting a new block: increase the indent level
        prettyJSONBuilder.append(charFromUnformattedJson);
        indentLevel++;
        appendIndentedNewLine(indentLevel, prettyJSONBuilder);
        break;
      case '}':
      case ']':
        // Ending a new block; decrese the indent level
        indentLevel--;
        appendIndentedNewLine(indentLevel, prettyJSONBuilder);
        prettyJSONBuilder.append(charFromUnformattedJson);
        break;
      case ',':
        // Ending a json item; create a new line after
        prettyJSONBuilder.append(charFromUnformattedJson);
        if(!inQuote) {
          appendIndentedNewLine(indentLevel, prettyJSONBuilder);
        }
        break;
      default:
        prettyJSONBuilder.append(charFromUnformattedJson);
    }
  }
  return prettyJSONBuilder.toString();
}

/**
 * Print a new line with indention at the beginning of the new line.
 * @param indentLevel
 * @param stringBuilder
 */
private static void appendIndentedNewLine(int indentLevel, StringBuilder stringBuilder) {
  stringBuilder.append("\n");
  for(int i = 0; i < indentLevel; i++) {
    // Assuming indention using 2 spaces
    stringBuilder.append("  ");
  }
}

You can use small json library

String jsonstring = ....;
JsonValue json = JsonParser.parse(jsonstring);
String jsonIndendedByTwoSpaces = json.toPrettyString("  ");

You can use Gson like below

Gson gson = new GsonBuilder().setPrettyPrinting().create();
String jsonString = gson.toJson(object);

From the post JSON pretty print using Gson

Alternatively, You can use Jackson like below

ObjectMapper mapper = new ObjectMapper();
String perttyStr = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(object);

From the post Pretty print JSON in Java (Jackson)

Hope this help!

With Jackson (com.fasterxml.jackson.databind):

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

From: How to enable pretty print JSON output (Jackson)

I know this is already in the answers, but I want to write it separately here because chances are, you already have Jackson as a dependency and so all you will need would be an extra line of code

This worked for me, using Jackson:

mapper.writerWithDefaultPrettyPrinter().writeValueAsString(JSONString)

Pretty printing with GSON in one line:

System.out.println(new GsonBuilder().setPrettyPrinting().create().toJson(new JsonParser().parse(jsonString)));

Besides inlining, this is equivalent to the accepted answer.

Using org json. Reference link

JSONObject jsonObject = new JSONObject(obj);
String prettyJson = jsonObject.toString(4);

Using Gson. Reference link

Gson gson = new GsonBuilder().setPrettyPrinting().create();
String json = gson.toJson(obj);

Using Jackson. Reference link

ObjectMapper mapper = new ObjectMapper();
mapper.enable(SerializationFeature.INDENT_OUTPUT);
String json = mapper.writeValueAsString(obj);

Using Genson. Reference link.

Genson prettyGenson = new GensonBuilder().useIndentation(true).create();
String prettyJson = prettyGenson.serialize(obj);

Now this can be achieved with the JSONLib library:

http://json-lib.sourceforge.net/apidocs/net/sf/json/JSONObject.html

If (and only if) you use the overloaded toString(int indentationFactor) method and not the standard toString() method.

I have verified this on the following version of the API:

<dependency>
  <groupId>org.json</groupId>
  <artifactId>json</artifactId>
  <version>20140107</version>
</dependency>