使用Jackson JSON Parser：复杂的JSON？

我有一个复杂的JSON，我试图使用Jackson JSON解析。 我对如何进入latLng对象以拉出lat，lng值感到有点困惑。 这是JSON的一部分：

{ "results": [ { "locations": [ { "latLng": { "lng": -76.85165, "lat": 39.25108 }, "adminArea4": "Howard County", "adminArea5Type": "City", "adminArea4Type": "County", 

到目前为止，我用Java来解决这个问题：

 public class parkJSON { public latLng _latLng; public static class latLng { private String _lat, _lng; public String getLat() { return _lat; } public String getLon() { return _lng; } } } 

和

 ObjectMapper mapper = new ObjectMapper(); // can reuse, share globally mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false); parkJSON geo = mapper.readValue(parse, parkJSON.class); System.out.println(mapper.writeValueAsString(geo)); String lat = geo._latLng.getLat(); String lon = geo._latLng.getLon(); output = lat + "," + lon; System.out.println("Found Coordinates: " + output); 

已解决这是我通过使用树模型以供将来参考解决问题的方法：

  ObjectMapper mapper = new ObjectMapper(); // can reuse, share globally mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false); JsonNode rootNode = mapper.readTree(parse); JsonNode firstResult = rootNode.get("results").get(0); JsonNode location = firstResult.get("locations").get(0); JsonNode latLng = location.get("latLng"); String lat = latLng.get("lat").asText(); String lng = latLng.get("lng").asText(); output = lat + "," + lng; System.out.println("Found Coordinates: " + output); 

Answer 1

如果你对这个输入结构真正感兴趣的是lat和lng完全映射可能是Jackson提供的不同方法中最不适应的，因为它迫使你编写类来表示数据中的不同层。

Jackson提供了两种替代方案，允许您在不必定义这些类的情况下提取这些字段：

1. 树模型提供了许多导航方法来遍历树并提取您感兴趣的数据。
2. 简单数据绑定将JSON文档映射到Map或List，然后可以使用这些集合提供的方法进行导航。

Jackson文档包含两种技术的示例，在程序中应用它们不应该太难，使用调试器调查解析器创建的数据结构，以查看文档是如何映射的。

Answer 2

无论你的json是什么：这里有一个实用程序，它可以转换为json2object或Object2json，

 import java.io.IOException; import java.io.StringWriter; import java.util.List; import com.fasterxml.jackson.core.JsonGenerationException; import com.fasterxml.jackson.core.JsonParseException; import com.fasterxml.jackson.core.type.TypeReference; import com.fasterxml.jackson.databind.DeserializationFeature; import com.fasterxml.jackson.databind.JsonMappingException; import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.SerializationFeature; /** * * @author TIAGO.MEDICI * */ public class JsonUtils { public static boolean isJSONValid(String jsonInString) { try { final ObjectMapper mapper = new ObjectMapper(); mapper.readTree(jsonInString); return true; } catch (IOException e) { return false; } } public static String serializeAsJsonString(Object object) throws JsonGenerationException, JsonMappingException, IOException { ObjectMapper objMapper = new ObjectMapper(); objMapper.enable(SerializationFeature.INDENT_OUTPUT); objMapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS); StringWriter sw = new StringWriter(); objMapper.writeValue(sw, object); return sw.toString(); } public static String serializeAsJsonString(Object object, boolean indent) throws JsonGenerationException, JsonMappingException, IOException { ObjectMapper objMapper = new ObjectMapper(); if (indent == true) { objMapper.enable(SerializationFeature.INDENT_OUTPUT); objMapper.disable(SerializationFeature.FAIL_ON_EMPTY_BEANS); } StringWriter stringWriter = new StringWriter(); objMapper.writeValue(stringWriter, object); return stringWriter.toString(); } public static  T jsonStringToObject(String content, Class clazz) throws JsonParseException, JsonMappingException, IOException { T obj = null; ObjectMapper objMapper = new ObjectMapper(); obj = objMapper.readValue(content, clazz); return obj; } @SuppressWarnings("rawtypes") public static  T jsonStringToObjectArray(String content) throws JsonParseException, JsonMappingException, IOException { T obj = null; ObjectMapper mapper = new ObjectMapper(); obj = mapper.readValue(content, new TypeReference() { }); return obj; } public static  T jsonStringToObjectArray(String content, Class clazz) throws JsonParseException, JsonMappingException, IOException { T obj = null; ObjectMapper mapper = new ObjectMapper(); mapper = new ObjectMapper().configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true); obj = mapper.readValue(content, mapper.getTypeFactory().constructCollectionType(List.class, clazz)); return obj; }