问题描述
我正在尝试使用 Jackson JsonParser 从一个大型 JSON 文件中一一读取事件。我想将每个事件临时存储在一个对象中，例如 JsonObject 或任何其他我以后想要用于进一步处理的对象。
我之前是一一读取 JSON 事件并将它们存储到我自己的自定义上下文中：Old Post for JACKSON JsonParser Context 工作正常。但是，我想将它们一一存储到 jsonObject 或其他对象中，而不是上下文。
以下是我的示例 JSON 文件：
{
"@context":"https://context.org/context.jsonld","isA":"SchoolManagement","format":"application/ld+json","schemaVersion":"2.0","creationDate":"2021-04-21T10:10:09+00:00","body":{
"members":[
{
"isA":"student","name":"ABCS","class":10,"coaching":[
"XSJSJ","IIIRIRI"
],"dob":"1995-04-21T10:10:09+00:00"
},{
"isA":"teacher","department":"computer science","school":{
"name":"ABCD School"
},{
"isA":"boardMember","board":"schoolboard","dob":"1995-04-21T10:10:09+00:00"
}
]
}
}
有时我只想在我的 member 中存储一个 student，例如 teacher 或 JsonObject。
以下是我到目前为止的代码： 将每个事件存储在一个对象中的最佳方法是什么，我以后可以使用它进行一些处理。 然后再次清除该对象并将其用于下一个事件？
public class Main {
private JSONObject eventInfo;
private final String[] eventTypes = new String[] { "student","teacher","boardMember" };
public static void main(String[] args) throws JsonParseException,JsonMappingException,IOException,JAXBException,URISyntaxException {
// Get the JSON Factory and parser Object
JsonFactory jsonFactory = new JsonFactory();
JsonParser jsonParser = jsonFactory.createParser(new File(Main.class.getClassLoader().getResource("inputJson.json").toURI()));
JsonToken current = jsonParser.nextToken();
// Check the first element is Object
if (current != JsonToken.START_OBJECT) {
throw new IllegalStateException("Expected content to be an array");
}
// Loop until the start of the EPCIS EventList array
while (jsonParser.nextToken() != JsonToken.START_ARRAY) {
System.out.println(jsonParser.getCurrentToken() + " --- " + jsonParser.getCurrentName());
}
// Goto the next token
jsonParser.nextToken();
// Call the method to loop until the end of the events file
eventTraverser(jsonParser);
}
// Method which will traverse through the eventList and read event one-by-one
private static void eventTraverser(JsonParser jsonParser) throws IOException {
// Loop until the end of the EPCIS events file
while (jsonParser.nextToken() != JsonToken.END_OBJECT) {
//Is there a possibility to store the complete object directly in an JSON Object or I need to again go through every token to see if is array and handle it accordingly as mentioned in my prevIoUs POST.
}
}
}
解决方法
在尝试了一些东西后，我能够让它工作。我发布了整个代码，因为它可能对将来的某个人有用，因为我知道找到合适的工作代码示例是多么令人沮丧：
public class Main
{
public void xmlConverter (InputStream jsonStream) throws IOException,JAXBException,XMLStreamException
{
// jsonStream is the input JSOn which is normally passed by reading the JSON file
// Get the JSON Factory and parser Object
final JsonFactory jsonFactory = new JsonFactory ();
final JsonParser jsonParser = jsonFactory.createParser (jsonStream);
final ObjectMapper objectMapper = new ObjectMapper ();
//To read the duplicate keys if there are any key duplicate json
final SimpleModule module = new SimpleModule ();
module.addDeserializer (JsonNode.class,new JsonNodeDupeFieldHandlingDeserializer ());
objectMapper.registerModule (module);
jsonParser.setCodec (objectMapper);
// Check the first element is Object if not then invalid JSON throw error
if (jsonParser.nextToken () != JsonToken.START_OBJECT)
{
throw new IllegalStateException ("Expected content to be an array");
}
while (!jsonParser.getText ().equals ("members"))
{
//Skipping the elements till members key
// if you want you can do some process here
// I am skipping for now
}
// Goto the next token
jsonParser.nextToken ();
while (jsonParser.nextToken () != JsonToken.END_ARRAY)
{
final JsonNode jsonNode = jsonParser.readValueAsTree ();
//Check if the JsonNode is valid if not then exit the process
if (jsonNode == null || jsonNode.isNull ())
{
System.out.println ("End Of File");
break;
}
// Get the eventType
final String eventType = jsonNode.get ("isA").asText ();
// Based on eventType call different type of class
switch (eventType)
{
case "student":
final Student studentInfo =
objectMapper.treeToValue (jsonNode,Student.class);
//I was calling the JAXB Method as I was doing the JSON to XML Conversion
xmlCreator (studentInfo,Student.class);
break;
case "teacher":
final Teacher teacherInfo =
objectMapper.treeToValue (jsonNode,Teacher.class);
xmlCreator (teacherInfo,Teacher.class);
break;
}
}
}
//Method to create the XML using the JAXB
private void xmlCreator (Object eventInfo,Class eventType) throws JAXBException
{
private final StringWriter sw = new StringWriter ();
// Create JAXB Context object
JAXBContext context = JAXBContext.newInstance (eventType);
// Create Marshaller object from JAXBContext
Marshaller marshaller = context.createMarshaller ();
// Print formatted XML
marshaller.setProperty (Marshaller.JAXB_FORMATTED_OUTPUT,Boolean.TRUE);
// Do not add the <xml> version tag
marshaller.setProperty (Marshaller.JAXB_FRAGMENT,Boolean.TRUE);
// XmlSupportExtension is an interface that every class such as Student Teacher implements
// xmlSupport is a method in XmlSupportExtension which has been implemented in all classes
// Create the XML based on type of incoming event type and store in SW
marshaller.marshal (((XmlSupportExtension) eventInfo).xmlSupport (),sw);
// Add each event within the List
eventsList.add (sw.toString ());
// Clear the StringWritter for next event
sw.getBuffer ().setLength (0);
}
}
这是覆盖 JACKSON 类的类。
如果您的 Json 具有重复的 JSON 密钥，则可以使用此方法。如果您需要，请关注此帖子以获得完整的说明。如果不需要，请跳过此部分并从上述类中删除代码 module 部分：
Jackson @JsonAnySetter ignores values of duplicate key when used with Jackson ObjectMapper treeToValue method
@JsonDeserialize(using = JsonNodeDupeFieldHandlingDeserializer.class)
public class JsonNodeDupeFieldHandlingDeserializer extends JsonNodeDeserializer {
@Override
protected void _handleDuplicateField(JsonParser p,DeserializationContext ctxt,JsonNodeFactory nodeFactory,String fieldName,ObjectNode objectNode,JsonNode oldValue,JsonNode newValue) {
ArrayNode asArrayValue = null;
if (oldValue.isArray()) {
asArrayValue = (ArrayNode) oldValue;
} else {
asArrayValue = nodeFactory.arrayNode();
asArrayValue.add(oldValue);
}
asArrayValue.add(newValue);
objectNode.set(fieldName,asArrayValue);
}
}