大多数现有的答案要么依赖于一些外部库，要么需要一个特殊的Java版本。下面是一个简单的代码来漂亮地打印一个JSON字符串，只使用一般的Java api(在Java 7中更高;虽然还没有尝试过旧版本)。

基本思想是基于JSON中的特殊字符来调整格式。例如，如果观察到'{'或'['，代码将创建一个新行并增加缩进级别。

免责声明:我只测试了一些简单的JSON情况(基本的键值对，列表，嵌套JSON)，所以它可能需要一些工作更一般的JSON文本，如字符串值内引号，或特殊字符(\n， \t等)。

/**
 * 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("  ");
  }
}

在JSONLib中，你可以这样使用:

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

来自Javadoc:

使用org json。参考链接

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

使用Gson。参考链接

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

使用杰克逊。参考链接

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

使用Genson的律师。参考链接。

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

使用javax.json。参考链接。

Map<String, Boolean> config = new HashMap<>();

config.put(JsonGenerator.PRETTY_PRINTING, true);

JsonWriterFactory writerFactory = Json.createWriterFactory(config);
Writer writer = new StringWriter();

writerFactory.createWriter(writer).write(jsonObject);

String json = writer.toString();

使用Moshi库。参考链接。

String json = jsonAdapter.indent("  ").toJson(emp1);

(OR)

Buffer buffer = new Buffer();
JsonWriter jsonWriter = JsonWriter.of(buffer);
jsonWriter.setIndent("   ");

jsonAdapter.toJson(jsonWriter, emp1);

json = buffer.readUtf8();

I also use the org.json.simple package. I have simply coded the formatter, but since I don't have nulls, numbers or booleans in my JSON objects in the program that I wrote, I only coded for strings, objects and arrays. If anyone is interested, let this just be in the public domain. You are welcome to add the missing data types (where it says in the comment "it's a string"). Also, you can add the indentation as a parameter whereas mine is just two spaces. Please reshare after you've tested your improvements.

用法： printJsonObject（jsonObject， “”）;

功能:

    public static void printJsonObject(JSONObject object, String prefix) {
        boolean notFirst = false;
        System.out.println(prefix + "{");
        for (Object key : object.keySet()) {
            if (notFirst) {
                System.out.println(", ");
            }
            notFirst = true;
            Object value = object.get(key);
            System.out.print(prefix + "  " + "\"" + key + "\"" + ": ");
            if (value instanceof JSONObject) {
                printJsonObject((JSONObject) value, prefix + "  ");
            } else if (value instanceof JSONArray) {
                printJsonArray((JSONArray) value, prefix + "  ");
            } else {  // it's a string
                System.out.print("\"" + value + "\"");
            }
        }
        System.out.println("");
        System.out.print(prefix + "}");
    }

    public static void printJsonArray(JSONArray array, String prefix) {
        boolean notFirst = false;
        System.out.println("[");
        for (Object item : array) {
            if (notFirst) {
                System.out.println(", ");
            }
            notFirst = true;
            if (item instanceof JSONObject) {
                printJsonObject((JSONObject) item, prefix + "  ");
            } else if (item instanceof JSONArray) {
                printJsonArray((JSONArray) item, prefix + "  ");
            } else {
                System.out.print(prefix + "  " + "\"" + item + "\"");
            }
        }
        System.out.println("");
        System.out.print(prefix + "]");
    }

这招对我很管用，用了杰克逊的话:

mapper.writerWithDefaultPrettyPrinter().writeValueAsString(JSONString)

这将是一个公共方法，用于打印对象的漂亮版本(你需要安装Gson依赖项:

import com.google.gson.GsonBuilder;
...

public void printMe(){
    Gson gson = new GsonBuilder().setPrettyPrinting().create();
    String prettyJSON = gson.toJson(this);
    System.out.println(printable);
}