在不知道 JSON 格式的情况下用 Java 解析 JSON [英] Parsing JSON in Java without knowing JSON format

问题描述

我正在尝试用 Java 解析 JSON 字符串并找到键值对，以便我可以确定 JSON 对象的大致结构，因为 JSON 字符串的对象结构是未知的.

例如，一个执行可能有一个像这样的 JSON 字符串:

 {"id" : 12345, "days" : [ "Monday", "Wednesday" ], "person" : { "firstName" : "David", "lastName" : "Menoyo" } }

还有一个这样的:

 {"url" : "http://someurl.com", "method" : "POST", "isauth" : false }

我将如何遍历各种 JSON 元素并确定键及其值?我查看了 jackson-core 的 JsonParser.我知道如何获取下一个令牌"并确定它是什么类型的令牌(即字段名称、值、数组开始等)，但是，我不知道如何获取实际令牌的值.

例如:

public void parse(String json) {尝试 {JsonFactory f = new JsonFactory();JsonParser 解析器 = f.createParser(json);JsonToken token = parser.nextToken();而(令牌！= null){if (token.equals(JsonToken.START_ARRAY)) {logger.debug("起始数组:" + token.toString());} else if (token.equals(JsonToken.END_ARRAY)) {logger.debug("结束数组:" + token.toString());} else if (token.equals(JsonToken.START_OBJECT)) {logger.debug("起始对象:" + token.toString());} else if (token.equals(JsonToken.END_OBJECT)) {logger.debug("结束对象:" + token.toString());} else if (token.equals(JsonToken.FIELD_NAME)) {logger.debug("字段名称:" + token.toString());} else if (token.equals(JsonToken.VALUE_FALSE)) {logger.debug("Value False:" + token.toString());} else if (token.equals(JsonToken.VALUE_NULL)) {logger.debug("值为空:" + token.toString());} else if (token.equals(JsonToken.VALUE_NUMBER_FLOAT)) {logger.debug("数值浮点数:" + token.toString());} else if (token.equals(JsonToken.VALUE_NUMBER_INT)) {logger.debug("Value Number Int:" + token.toString());} else if (token.equals(JsonToken.VALUE_STRING)) {logger.debug("值字符串:" + token.toString());} else if (token.equals(JsonToken.VALUE_TRUE)) {logger.debug("值真:" + token.toString());} 别的 {logger.debug("别的东西:" + token.toString());}token = parser.nextToken();}} 捕获(异常 e){logger.error("", e);}}

jackson 或其他一些库(gson 或 simple-json)中是否有一个生成树的类，或允许一个类循环遍历 json 元素并获取实际的键名和值?

解决方案

看一看 Jacksons 内置树模型功能.

您的代码将是:

public void parse(String json) {JsonFactory 工厂 = new JsonFactory();ObjectMapper mapper = new ObjectMapper(factory);JsonNode rootNode = mapper.readTree(json);Iterator>fieldsIterator = rootNode.fields();而 (fieldsIterator.hasNext()) {Map.Entryfield = fieldsIterator.next();System.out.println("Key:" + field.getKey() + "	Value:" + field.getValue());}}

I am trying to parse JSON strings in Java and find the key-value pairs so that I can determine the approximate structure of the JSON object since object structure of JSON string is unknown.

For example, one execution may have a JSON string like this:

  {"id" : 12345, "days" : [ "Monday", "Wednesday" ], "person" : { "firstName" : "David", "lastName" : "Menoyo" } }

And another like this:

  {"url" : "http://someurl.com", "method" : "POST", "isauth" : false }

How would I cycle through the various JSON elements and determine the keys and their values? I looked at jackson-core's JsonParser. I see how I can grab the next "token" and determine what type of token it is (i.e., field name, value, array start, etc), but, I don't know how to grab the actual token's value.

For example:

public void parse(String json)  {
  try {
     JsonFactory f = new JsonFactory();
     JsonParser parser = f.createParser(json);
     JsonToken token = parser.nextToken();
     while (token != null) {
        if (token.equals(JsonToken.START_ARRAY)) {
           logger.debug("Start Array : " + token.toString());
        } else if (token.equals(JsonToken.END_ARRAY)) {
           logger.debug("End Array : " + token.toString());
        } else if (token.equals(JsonToken.START_OBJECT)) {
           logger.debug("Start Object : " + token.toString());
        } else if (token.equals(JsonToken.END_OBJECT)) {
           logger.debug("End Object : " + token.toString());
        } else if (token.equals(JsonToken.FIELD_NAME)) {
           logger.debug("Field Name : " + token.toString());
        } else if (token.equals(JsonToken.VALUE_FALSE)) {
           logger.debug("Value False : " + token.toString());
        } else if (token.equals(JsonToken.VALUE_NULL)) {
           logger.debug("Value Null : " + token.toString());
        } else if (token.equals(JsonToken.VALUE_NUMBER_FLOAT)) {
           logger.debug("Value Number Float : " + token.toString());
        } else if (token.equals(JsonToken.VALUE_NUMBER_INT)) {
          logger.debug("Value Number Int : " + token.toString());
        } else if (token.equals(JsonToken.VALUE_STRING)) {
           logger.debug("Value String : " + token.toString());
        } else if (token.equals(JsonToken.VALUE_TRUE)) {
           logger.debug("Value True : " + token.toString());
        } else {
           logger.debug("Something else : " + token.toString());
        }
        token = parser.nextToken();
     }
  } catch (Exception e) {
     logger.error("", e);
  }
}

Is there a class in jackson or some other library (gson or simple-json) that produces a tree, or allows one to cycle through the json elements and obtain the actual key names in addition to the values?

解决方案

Take a look at Jacksons built-in tree model feature.

And your code will be:

public void parse(String json)  {
       JsonFactory factory = new JsonFactory();

       ObjectMapper mapper = new ObjectMapper(factory);
       JsonNode rootNode = mapper.readTree(json);  

       Iterator<Map.Entry<String,JsonNode>> fieldsIterator = rootNode.fields();
       while (fieldsIterator.hasNext()) {

           Map.Entry<String,JsonNode> field = fieldsIterator.next();
           System.out.println("Key: " + field.getKey() + "	Value:" + field.getValue());
       }
}

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