使用Google的Gson进行严格的JSON解析？

使用Google的Gson进行严格的JSON解析？

Gson没有JSON模式验证功能来指定必须存在一个特定的元素，也没有办法指定必须填充Java成员。拥有这样的功能（例如带有

@Required

注释）可能会很好。转到“
Gson问题列表”
并提出增强请求。

使用Gson，您可以强制使用自定义反序列化器提供指定的JSON元素。

// output: //   [MyObject: element1=value1, element2=value2, element3=value3]//   [MyObject: element1=value1, element2=value2, element3=null]//   Exception in thread "main" com.google.gson.JsonParseException: Required Field Not Found: element2import java.lang.reflect.Type;import java.util.ArrayList;import java.util.List;import com.google.gson.Gson;import com.google.gson.GsonBuilder;import com.google.gson.JsonDeserializationContext;import com.google.gson.JsonDeserializer;import com.google.gson.JsonElement;import com.google.gson.JsonObject;import com.google.gson.JsonParseException;public class Foo{  static String jsonInput1 = "{"element1":"value1","element2":"value2","element3":"value3"}";  static String jsonInput2 = "{"element1":"value1","element2":"value2"}";  static String jsonInput3 = "{"element1":"value1","element3":"value3"}";  public static void main(String[] args)  {    GsonBuilder gsonBuilder = new GsonBuilder();    MyDeserializer deserializer = new MyDeserializer();    deserializer.registerRequiredField("element2");    gsonBuilder.registerTypeAdapter(MyObject.class, deserializer);    Gson gson = gsonBuilder.create();    MyObject object1 = gson.fromJson(jsonInput1, MyObject.class);    System.out.println(object1);    MyObject object2 = gson.fromJson(jsonInput2, MyObject.class);    System.out.println(object2);    MyObject object3 = gson.fromJson(jsonInput3, MyObject.class);    System.out.println(object3);  }}class MyObject{  String element1;  String element2;  String element3;  @Override  public String toString()  {    return String.format(        "[MyObject: element1=%s, element2=%s, element3=%s]",        element1, element2, element3);  }}class MyDeserializer implements JsonDeserializer<MyObject>{  List<String> requiredFields = new ArrayList<String>();  void registerRequiredField(String fieldName)  {    requiredFields.add(fieldName);  }  @Override  public MyObject deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)      throws JsonParseException  {    JsonObject jsonObject = (JsonObject) json;    for (String fieldName : requiredFields)    {      if (jsonObject.get(fieldName) == null)      {        throw new JsonParseException("Required Field Not Found: " + fieldName);      }    }    return new Gson().fromJson(json, MyObject.class);  }}

一种更好的方法可能是使用提供JSON模式验证的API 。
杰克逊至少有一个基本的实施方案。
JSON工具似乎已经成熟了。

这是杰克逊的一个例子。

// output: // Validating jsonInput1...// Validating jsonInput2...// Validating jsonInput3...// $.element2: is missing and it is not optional// [MyObject: element1=value1, element2=value2, element3=value3]// [MyObject: element1=value1, element2=value2, element3=null]// [MyObject: element1=value1, element2=null, element3=value3]import java.util.List;import org.prehaus.jackson.map.ObjectMapper;import eu.vahlas.json.schema.JSONSchema;import eu.vahlas.json.schema.JSONSchemaProvider;import eu.vahlas.json.schema.impl.JacksonSchemaProvider;public class Foo{  static String jsonSchema =     "{" +         ""description":"Serialized MyObject Specification"," +         ""type":["object"]," +         ""properties":" +         "{" +  ""element1":{"type":"string"}," +  ""element2":{"type":"string","optional":false}," +  ""element3":{"type":"string","optional":true}" +         "}" +     "}";;  static String jsonInput1 = "{"element1":"value1","element2":"value2","element3":"value3"}";  static String jsonInput2 = "{"element1":"value1","element2":"value2"}";  static String jsonInput3 = "{"element1":"value1","element3":"value3"}";  public static void main(String[] args) throws Exception  {    ObjectMapper mapper = new ObjectMapper();    JSonSchemaProvider schemaProvider = new JacksonSchemaProvider(mapper);    JSonSchema schema = schemaProvider.getSchema(jsonSchema);    System.out.println("Validating jsonInput1...");    validateAndLogErrors(jsonInput1, schema);    System.out.println("Validating jsonInput2...");    validateAndLogErrors(jsonInput2, schema);    System.out.println("Validating jsonInput3...");    validateAndLogErrors(jsonInput3, schema);    MyObject object1 = mapper.readValue(jsonInput1, MyObject.class);    System.out.println(object1);    MyObject object2 = mapper.readValue(jsonInput2, MyObject.class);    System.out.println(object2);    MyObject object3 = mapper.readValue(jsonInput3, MyObject.class);    System.out.println(object3);  }  static void validateAndLogErrors(String jsonInput, JSonSchema schema)  {    List<String> errors = schema.validate(jsonInput);    for (String error : errors)    {      System.out.println(error);    }  }}class MyObject{  String element1;  String element2;  String element3;  void setElement1(String element1)  {    this.element1 = element1;  }  void setElement2(String element2)  {    this.element2 = element2;  }  void setElement3(String element3)  {    this.element3 = element3;  }  @Override  public String toString()  {    return String.format(        "[MyObject: element1=%s, element2=%s, element3=%s]",        element1, element2, element3);  }}