如何使用 ResponseEntity 返回 JSONObject 而不是 HashMap？ （未找到类型返回值的转换器：类 org.json.JSONObject）
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【中文标题】如何使用 ResponseEntity 返回 JSONObject 而不是 HashMap？ （未找到类型返回值的转换器：类 org.json.JSONObject）【英文标题】：How to return a JSONObject instead HashMap with ResponseEntity? (No converter found for return value of type: class org.json.JSONObject) 【发布时间】：2019-02-23 15:23:41 【问题描述】：我能够从基于 Spring Boot 构建的 REST API 以 JSON 形式返回 HashMap。这是我的方法：
@ResponseBody
@Transactional
@GetMapping("create_coinmarketcap_snapshot")
public ResponseEntity<HashMap> create_coinmarketcap_snapshot()
String jsonString = callURL("https://api.coinmarketcap.com/v2/ticker/?limit=5");
JSONArray coinmarketcapsnapshotsArray = new JSONArray();
JSONObject coinmarketcapsnapshotsJSONObject = new JSONObject();
HashMap<Integer, CoinmarketcapSnapshot> coinmarketcapsnapshotsHashMap = new HashMap<>();
try
JSONObject jsonObject = new JSONObject(jsonString);
JSONObject jsonObjectData = jsonObject.getJSONObject("data");
Iterator<?> keys = jsonObjectData.keys();
int count = 0;
while (keys.hasNext())
count++;
String key = (String) keys.next();
if (jsonObjectData.get(key) instanceof JSONObject)
JSONObject jsonObjectDataCrypto = jsonObjectData.getJSONObject(key);
JSONObject jsonObjectDataCryptoQuotes = jsonObjectDataCrypto.getJSONObject("quotes").getJSONObject("USD");
CoinmarketcapSnapshot coinmarketcapsnapshotObject = new CoinmarketcapSnapshot();
String dateFormatted = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss").format(Calendar.getInstance().getTime());
coinmarketcapsnapshotObject.setTitle(jsonObjectDataCrypto.get("name") + " - " + dateFormatted);
coinmarketcapsnapshotObject.setCryptocurrencyId((int) jsonObjectDataCrypto.get("id"));
if(jsonObjectDataCrypto.get("rank")!=null)
coinmarketcapsnapshotObject.setRank((int) jsonObjectDataCrypto.get("rank"));
if(jsonObjectDataCrypto.get("circulating_supply")!=null)
coinmarketcapsnapshotObject.setCirculatingSupply((Double) jsonObjectDataCrypto.get("circulating_supply"));
if(jsonObjectDataCrypto.get("total_supply")!=null)
coinmarketcapsnapshotObject.setTotalSupply((Double) jsonObjectDataCrypto.get("total_supply"));
if(!jsonObjectDataCrypto.isNull("circulating_supply"))
coinmarketcapsnapshotObject.setMaxSupply((Double) jsonObjectDataCrypto.get("circulating_supply"));
if(!jsonObjectDataCrypto.isNull("total_supply"))
coinmarketcapsnapshotObject.setMaxSupply((Double) jsonObjectDataCrypto.get("total_supply"));
if(!jsonObjectDataCrypto.isNull("max_supply"))
coinmarketcapsnapshotObject.setMaxSupply((Double) jsonObjectDataCrypto.get("max_supply"));
if(!jsonObjectDataCryptoQuotes.isNull("price"))
coinmarketcapsnapshotObject.setPrice((Double) jsonObjectDataCryptoQuotes.get("price"));
if(!jsonObjectDataCryptoQuotes.isNull("volume_24h"))
coinmarketcapsnapshotObject.setVolume24h((Double) jsonObjectDataCryptoQuotes.get("volume_24h"));
if(!jsonObjectDataCryptoQuotes.isNull("market_cap"))
coinmarketcapsnapshotObject.setMarketCap((Double) jsonObjectDataCryptoQuotes.get("market_cap"));
if(!jsonObjectDataCryptoQuotes.isNull("percent_change_1h"))
coinmarketcapsnapshotObject.setPercentChange1h((Double) jsonObjectDataCryptoQuotes.get("percent_change_1h"));
if(!jsonObjectDataCryptoQuotes.isNull("percent_change_24h"))
coinmarketcapsnapshotObject.setPercentChange24h((Double) jsonObjectDataCryptoQuotes.get("percent_change_24h"));
if(!jsonObjectDataCryptoQuotes.isNull("percent_change_7d"))
coinmarketcapsnapshotObject.setPercentChange7d((Double) jsonObjectDataCryptoQuotes.get("percent_change_7d"));
entityManager.persist(coinmarketcapsnapshotObject);
coinmarketcapsnapshotsArray.put(coinmarketcapsnapshotObject);
coinmarketcapsnapshotsJSONObject.put(String.valueOf(count),coinmarketcapsnapshotObject);
coinmarketcapsnapshotsHashMap.put(count, coinmarketcapsnapshotObject);
catch (JSONException e)
e.printStackTrace();
System.out.println("\n\ncoinmarketcapsnapshotsArray:\n"+coinmarketcapsnapshotsArray);
System.out.println("\n\ncoinmarketcapsnapshotsJSONObject:\n"+coinmarketcapsnapshotsJSONObject);
System.out.println("\n\ncoinmarketcapsnapshotsHashMap:\n"+coinmarketcapsnapshotsHashMap);
return new ResponseEntity<>(coinmarketcapsnapshotsHashMap, HttpStatus.OK);
这是终端打印的内容：
coinmarketcapsnapshotsArray:
["com.krown.entity.CoinmarketcapSnapshot@4d60f69f","com.krown.entity.CoinmarketcapSnapshot@4739c2f2","com.krown.entity.CoinmarketcapSnapshot@7d5bd573","com.krown.entity.CoinmarketcapSnapshot@43b5eb6d","com.krown.entity.CoinmarketcapSnapshot@26e1a633"]
coinmarketcapsnapshotsJSONObject:
"1":"com.krown.entity.CoinmarketcapSnapshot@4d60f69f","2":"com.krown.entity.CoinmarketcapSnapshot@4739c2f2","3":"com.krown.entity.CoinmarketcapSnapshot@7d5bd573","4":"com.krown.entity.CoinmarketcapSnapshot@43b5eb6d","5":"com.krown.entity.CoinmarketcapSnapshot@26e1a633"
coinmarketcapsnapshotsHashMap:
1=com.krown.entity.CoinmarketcapSnapshot@4d60f69f, 2=com.krown.entity.CoinmarketcapSnapshot@4739c2f2, 3=com.krown.entity.CoinmarketcapSnapshot@7d5bd573, 4=com.krown.entity.CoinmarketcapSnapshot@43b5eb6d, 5=com.krown.entity.CoinmarketcapSnapshot@26e1a633
我想返回我的 JSONObject“coinmarketcapsnapshotsJSONObject”而不是“coinmarketcapsnapshotsHashMap”，但是当我这样做时，我一直遇到这个错误：
没有找到返回值类型的转换器：class org.json.JSONObject
正如在网上找到的一些帖子中所建议的，我在 pom.xml 文件中添加了 Jackson 作为新依赖项：
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.5.0</version>
</dependency>
很遗憾，这并没有改变任何东西。
您有什么建议可以改进在 Spring Boot 上为 REST API 构建 JSON 的过程吗？
当我返回 HashMap 时，输出如下所示：
【问题讨论】：
为什么要转成JSONObject？默认情况下，Jackson 会为您执行此操作 您是否尝试调用您的休息服务？当您调用此休息服务时，您得到了什么？因为您没有在日志中覆盖“CoinmarketcapSnapshot”中的tostring() 方法，所以它只是打印toString() 表示
@MaruthiAdithya 我是 Java 新手，我不明白为什么我们需要这么多不同的库来遍历 JSON 对象并返回 JSON。由于我已经需要 JSON 对象，所以我想避免使用 HashMap。
@Deadpool，REST 服务在我返回 HashMap 时运行良好，但在返回 JSONObject 时不起作用。我将更新答案以显示输出。
那你为什么要返回JSONObject？
【参考方案1】：
HttpStatus.OK 是使用 Spring 的 Http 端点的默认返回值，因此不需要指定它，从而使整个 ResponseEntity 变得不必要：
@ResponseBody
@Transactional
@GetMapping("create_coinmarketcap_snapshot")
public HashMap create_coinmarketcap_snapshot()
String jsonString = callURL("https://api.coinmarketcap.com/v2/ticker/?limit=5");
JSONArray coinmarketcapsnapshotsArray = new JSONArray();
JSONObject coinmarketcapsnapshotsJSONObject = new JSONObject();
HashMap<Integer, CoinmarketcapSnapshot> coinmarketcapsnapshotsHashMap = new HashMap<>();
try
JSONObject jsonObject = new JSONObject(jsonString);
JSONObject jsonObjectData = jsonObject.getJSONObject("data");
Iterator<?> keys = jsonObjectData.keys();
int count = 0;
while (keys.hasNext())
count++;
String key = (String) keys.next();
if (jsonObjectData.get(key) instanceof JSONObject)
JSONObject jsonObjectDataCrypto = jsonObjectData.getJSONObject(key);
JSONObject jsonObjectDataCryptoQuotes = jsonObjectDataCrypto.getJSONObject("quotes").getJSONObject("USD");
CoinmarketcapSnapshot coinmarketcapsnapshotObject = new CoinmarketcapSnapshot();
String dateFormatted = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss").format(Calendar.getInstance().getTime());
coinmarketcapsnapshotObject.setTitle(jsonObjectDataCrypto.get("name") + " - " + dateFormatted);
coinmarketcapsnapshotObject.setCryptocurrencyId((int) jsonObjectDataCrypto.get("id"));
if(jsonObjectDataCrypto.get("rank")!=null)
coinmarketcapsnapshotObject.setRank((int) jsonObjectDataCrypto.get("rank"));
if(jsonObjectDataCrypto.get("circulating_supply")!=null)
coinmarketcapsnapshotObject.setCirculatingSupply((Double) jsonObjectDataCrypto.get("circulating_supply"));
if(jsonObjectDataCrypto.get("total_supply")!=null)
coinmarketcapsnapshotObject.setTotalSupply((Double) jsonObjectDataCrypto.get("total_supply"));
if(!jsonObjectDataCrypto.isNull("circulating_supply"))
coinmarketcapsnapshotObject.setMaxSupply((Double) jsonObjectDataCrypto.get("circulating_supply"));
if(!jsonObjectDataCrypto.isNull("total_supply"))
coinmarketcapsnapshotObject.setMaxSupply((Double) jsonObjectDataCrypto.get("total_supply"));
if(!jsonObjectDataCrypto.isNull("max_supply"))
coinmarketcapsnapshotObject.setMaxSupply((Double) jsonObjectDataCrypto.get("max_supply"));
if(!jsonObjectDataCryptoQuotes.isNull("price"))
coinmarketcapsnapshotObject.setPrice((Double) jsonObjectDataCryptoQuotes.get("price"));
if(!jsonObjectDataCryptoQuotes.isNull("volume_24h"))
coinmarketcapsnapshotObject.setVolume24h((Double) jsonObjectDataCryptoQuotes.get("volume_24h"));
if(!jsonObjectDataCryptoQuotes.isNull("market_cap"))
coinmarketcapsnapshotObject.setMarketCap((Double) jsonObjectDataCryptoQuotes.get("market_cap"));
if(!jsonObjectDataCryptoQuotes.isNull("percent_change_1h"))
coinmarketcapsnapshotObject.setPercentChange1h((Double) jsonObjectDataCryptoQuotes.get("percent_change_1h"));
if(!jsonObjectDataCryptoQuotes.isNull("percent_change_24h"))
coinmarketcapsnapshotObject.setPercentChange24h((Double) jsonObjectDataCryptoQuotes.get("percent_change_24h"));
if(!jsonObjectDataCryptoQuotes.isNull("percent_change_7d"))
coinmarketcapsnapshotObject.setPercentChange7d((Double) jsonObjectDataCryptoQuotes.get("percent_change_7d"));
entityManager.persist(coinmarketcapsnapshotObject);
coinmarketcapsnapshotsArray.put(coinmarketcapsnapshotObject);
coinmarketcapsnapshotsJSONObject.put(String.valueOf(count),coinmarketcapsnapshotObject);
coinmarketcapsnapshotsHashMap.put(count, coinmarketcapsnapshotObject);
catch (JSONException e)
e.printStackTrace();
System.out.println("\n\ncoinmarketcapsnapshotsArray:\n"+coinmarketcapsnapshotsArray);
System.out.println("\n\ncoinmarketcapsnapshotsJSONObject:\n"+coinmarketcapsnapshotsJSONObject);
System.out.println("\n\ncoinmarketcapsnapshotsHashMap:\n"+coinmarketcapsnapshotsHashMap);
return coinmarketcapsnapshotsHashMap;
【讨论】：
【参考方案2】：@GetMapping(produces=MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<?> create_coinmarketcap_snapshot() throws IOException
UriComponentsBuilder builder =
UriComponentsBuilder.fromUriString("https://api.coinmarketcap.com/v2/ticker")
.queryParam("limit", "5");
ResponseEntity<String> response =
restTemplate.getForEntity(builder.toUriString(), String.class);
ObjectMapper mapper = new ObjectMapper();
JsonNode root = mapper.readTree(response.getBody());
JsonNode data = root.path("data");
data.forEach(jsonObject ->
jsonObject.get("rank"); //extracting values from each json object
jsonObject.get("circulating_supply");
jsonObject.get("total_supply");
jsonObject.get("max_supply");
jsonObject.get("price");
jsonObject.get("volume_24h");
jsonObject.get("market_cap");
jsonObject.get("percent_change_1h");
jsonObject.get("percent_change_24h");
//... and so on
);
return ResponseEntity.ok(data);
现在您返回一个 json 对象，其中包含“数据”键 @118218 的值
【讨论】：
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