如何使用Jackson来反序列化对象数组

Jackson数据绑定文档表明Jackson支持反序列化“所有受支持类型的数组”，但是我无法确定确切的语法。

对于单个对象，我可以这样做：

//json input
{"id" : "junk","stuff" : "things"
}//Java
MyClass instance = objectMapper.readValue(json, MyClass.class);

现在，对于数组，我想这样做：

//json input
[{"id" : "junk","stuff" : "things"
},
{"id" : "spam","stuff" : "eggs"
}]//Java
List<MyClass> entries = ?

有人知道是否有不可思议的命令吗？如果没有，那么解决方案是什么？

#1楼

从Eugene Tskhovrebov

List<MyClass> myObjects = Arrays.asList(mapper.readValue(json, MyClass[].class))

这个解决方案似乎对我来说是最好的

#2楼

try {ObjectMapper mapper = new ObjectMapper();JsonFactory f = new JsonFactory();List<User> lstUser = null;JsonParser jp = f.createJsonParser(new File("C:\\maven\\user.json"));TypeReference<List<User>> tRef = new TypeReference<List<User>>() {};lstUser = mapper.readValue(jp, tRef);for (User user : lstUser) {System.out.println(user.toString());}} catch (JsonGenerationException e) {e.printStackTrace();
} catch (JsonMappingException e) {e.printStackTrace();
} catch (IOException e) {e.printStackTrace();
}

#3楼

对于通用实现：

public static <T> List<T> parseJsonArray(String json,Class<T> classOnWhichArrayIsDefined) throws IOException, ClassNotFoundException {ObjectMapper mapper = new ObjectMapper();Class<T[]> arrayClass = (Class<T[]>) Class.forName("[L" + classOnWhichArrayIsDefined.getName() + ";");T[] objects = mapper.readValue(json, arrayClass);return Arrays.asList(objects);
}

#4楼

首先创建一个线程安全的ObjectReader实例。

ObjectMapper objectMapper = new ObjectMapper();
ObjectReader objectReader = objectMapper.reader().forType(new TypeReference<List<MyClass>>(){});

然后使用它：

List<MyClass> result = objectReader.readValue(inputStream);

#5楼

这是一个可以转换json2object或Object2json的实用程序，无论您的pojo（实体T）如何

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> T jsonStringToObject(String content, Class<T> clazz) throws JsonParseException, JsonMappingException, IOException {T obj = null;ObjectMapper objMapper = new ObjectMapper();obj = objMapper.readValue(content, clazz);return obj;}@SuppressWarnings("rawtypes")public static <T> T jsonStringToObjectArray(String content) throws JsonParseException, JsonMappingException, IOException {T obj = null;ObjectMapper mapper = new ObjectMapper();obj = mapper.readValue(content, new TypeReference<List>() {});return obj;}public static <T> T jsonStringToObjectArray(String content, Class<T> 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;}

#6楼

首先创建一个映射器：

import com.fasterxml.jackson.databind.ObjectMapper;// in play 2.3
ObjectMapper mapper = new ObjectMapper();

作为数组：

MyClass[] myObjects = mapper.readValue(json, MyClass[].class);

作为列表：

List<MyClass> myObjects = mapper.readValue(jsonInput, new TypeReference<List<MyClass>>(){});

指定列表类型的另一种方法：

List<MyClass> myObjects = mapper.readValue(jsonInput, mapper.getTypeFactory().constructCollectionType(List.class, MyClass.class));

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