如果您正在使用用于JSON处理(JSR-353)实现的Java API，那么您可以指定JsonGenerator。当您创建JsonGeneratorFactory时，PRETTY_PRINTING属性。

下面的例子最初发表在我的博客文章中。

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();

GSON似乎支持这一点，尽管我不知道您是否想从正在使用的库切换。

来自用户指南:

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

与杰克逊(com.fasterxml.jackson.databind):

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

如何启用漂亮的JSON打印输出(Jackson)

我知道这已经在答案中，但我想在这里单独写它，因为很可能您已经将Jackson作为依赖项，因此您需要的只是额外的一行代码

所以我也很喜欢json-simple lib，并研究了如何打印它的输出。不幸的是，虽然这是一个悬而未决的问题，但我找不到它的任何代码。所以我想我应该试一试，这是我想出的(使用他们自己的来源)..

public class JsonPrinter {
  
  
  
  public static String toJson(Map<?,?> map) {
    StringBuilder out = new StringBuilder(32);
    new JsonPrinter(out).print(map);
    return out.toString();
  }
  
  
  public static String toJson(List<?> list) {
    StringBuilder out = new StringBuilder(32);
    new JsonPrinter(out).print(list);
    return out.toString();
  }
  
  
  
  
  
  
  
  private final Appendable out;
  private final String indentUnit;
  private final String newLine;
  
  
  private int indents;
  
  public JsonPrinter(Appendable out) {
    this(out, "  ", System.lineSeparator());
  }

  /**
   * 
   */
  public JsonPrinter(Appendable out, String indentUnit, String newLine) {
    this.out = Objects.requireNonNull(out, "null out");
    this.indentUnit = Objects.requireNonNull(indentUnit, "null indentUnit");
    this.newLine = Objects.requireNonNull(newLine, "null newLine");
    
    if (!indentUnit.isBlank())
      throw new IllegalArgumentException(
          "indentUnit must be a blank sequence (quoted): '" + indentUnit + "'");
    if (!"\r\n".equals(newLine) && ! "\n".equals(newLine))
      throw new IllegalArgumentException(
          "unrecognized newLine (quoted): '" + newLine + "'");
  }
  
  
  public void print(List<?> list) throws UncheckedIOException {
    try {
      assert indents == 0;
      printImpl(list);
      assert indents == 0;
    } catch (IOException iox) {
      throw new UncheckedIOException("on print(List): " + list, iox);
    }
  }
  
  
  public void print(Map<?,?> map) throws UncheckedIOException {
    try {
      assert indents == 0;
      printImpl(map);
      assert indents == 0;
    } catch (IOException iox) {
      throw new UncheckedIOException("on print(Map): " + map, iox);
    }
  }
  
  
  protected void printImpl(List<?> list) throws IOException {
    if (list == null) {
      out.append("null");
      return;
    }
    
    
    boolean first = true;
    var iter = list.iterator();
    
    open('[');
    while (iter.hasNext()) {
      if (first)
        first = false;
      else
        out.append(',');
      
      out.append(newLine);
      appendIndents();
      
      appendValue(iter.next());
    }
    close(']');
  }
  
  
  protected void printImpl(Map<?, ?> map) throws IOException {
    if (map == null) {
      out.append("null");
      return;
    }
    
    
    boolean first = true;
    var iter = map.entrySet().iterator();
    
    open('{');
    while (iter.hasNext()) {
      if (first)
        first = false;
      else
        out.append(',');
      
      out.append(newLine);
      appendIndents();
      
      var entry = iter.next();
      print(entry.getKey().toString(), entry.getValue());
    }
    close('}');
  }
  
  
  private void open(char c) throws IOException {
    out.append(c);
    ++indents;
  }
  
  private void close(char c) throws IOException {
    --indents;
    out.append(newLine);
    appendIndents();
    out.append(c);
  }
  
  private void appendIndents() throws IOException {
    for (int count = indents; count-- > 0; )
      out.append(indentUnit);
  }
  
  
  
  private void print(String key, Object value) throws IOException {
    out.append('"');
    appendString(key);
    out.append('"').append(':').append(' ');
    appendValue(value);
  }
  
  
  
  private void appendString(String s) throws IOException {
    for (int i = 0; i < s.length(); i++) {
      char ch = s.charAt(i);
      switch(ch){
      case '"':
        out.append("\\\"");
        break;
      case '\\':
        out.append("\\\\");
        break;
      case '\b':
        out.append("\\b");
        break;
      case '\f':
        out.append("\\f");
        break;
      case '\n':
        out.append("\\n");
        break;
      case '\r':
        out.append("\\r");
        break;
      case '\t':
        out.append("\\t");
        break;
      case '/':
        out.append("\\/");
        break;
      default:
                //Reference: http://www.unicode.org/versions/Unicode5.1.0/
        if ((ch>='\u0000' && ch<='\u001F') || (ch>='\u007F' && ch<='\u009F') || (ch>='\u2000' && ch<='\u20FF')) {
          String ss = Integer.toHexString(ch);
          out.append("\\u");
          for (int k=0; k < 4-ss.length(); k++) {
            out.append('0');
          }
          out.append(ss.toUpperCase());
        }
        else{
          out.append(ch);
        }
      }
    }//for
  }
  
  
  private void appendValue(Object value) throws IOException {
    if (value == null) {
      out.append("null");
      
    } else if (value instanceof String) {
      out.append('"');
      appendString(value.toString());
      out.append('"');
      
    } else if (value instanceof Double) {
      var num = (Double) value;
      if (num.isInfinite() || num.isNaN())
        out.append("null");
      else
        out.append(value.toString());
      
    } else if (value instanceof Float) {
      var num = (Float) value;
      if (num.isInfinite() || num.isNaN())
        out.append("null");
      else
        out.append(value.toString());
      
    } else if (value instanceof Map) {
      printImpl((Map<?,?>) value);
      
    } else if (value instanceof List) {
      printImpl((List<?>) value);
      
//    } else if (value instanceof Number || value instanceof Boolean) {
//      out.append(value.toString());
      
    } else {
      out.append(value.toString());
      
    }
  }

}

它适用于JSONObject和JSONArray，即使它没有依赖于他们..因为这些是常规的Map和List对象。(事实代码是从同一个库中提取的)。

https://github.com/crums-io/io-util/blob/master/src/main/java/io/crums/util/json/JsonPrinter.java

谷歌的GSON可以很好地做到这一点:

Gson gson = new GsonBuilder().setPrettyPrinting().create();
JsonParser jp = new JsonParser();
JsonElement je = jp.parse(uglyJsonString);
String prettyJsonString = gson.toJson(je);

或者因为现在推荐使用来自JsonParser的静态解析方法，你也可以使用这个代替:

Gson gson = new GsonBuilder().setPrettyPrinting().create();
JsonElement je = JsonParser.parseString​(uglyJsonString);
String prettyJsonString = gson.toJson(je);

下面是导入语句:

import com.google.gson.*;

这是Gradle的依赖项:

implementation 'com.google.code.gson:gson:2.8.7'

我用的是org。Json内置方法来漂亮地打印数据。

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

JSON中每个定义的字段顺序是随机的。具体的顺序取决于解析器的实现。